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BSCBO- 101, , B. Sc. I YEAR, , Microbiology, Mycology and Plant, Pathology, , DEPARTMENT OF BOTANY, SCHOOL OF SCIENCES, UTTARAKHAND OPEN UNIVERSITY
Page 2 : MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , BSCBO-101, , MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , SCHOOL OF SCIENCES, DEPARTMENT OF BOTANY, UTTARAKHAND OPEN UNIVERSITY, , Phone No. 05946-261122, 261123, Toll free No. 18001804025, Fax No. 05946-264232, E. mail
[email protected], htpp://uou.ac.in, , UTTARAKHAND OPEN UNIVERSITY, , Page 1
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , CONTENTS, BLOCK-1-GENERAL MICROBIOLOGY, Unit-1-General account, distribution and classification of microorganisms,, Major microbes of food, water and soil, , PAGE NO., 7-40, , Unit-2-Isolation and Cultivation of Microorganisms, Instruments used, in Microbiological studies, , 41-68, , Unit-3-Structure, Classification, Nutrition, Reproduction and Economic, importance of Bacteria, , 69-91, , Unit-4-General account, Classification, Structure, Reproduction and, Economic importance of Viruses, , 92-106, , BLOCK-2- FUNGI AND LICHENS, , PAGE NO., , Unit-5- Characters, Economic importance, Classification and, General account of major classes of Fungi, , 108-140, , Unit-6- General account, Habit, Structure and Methods of reproduction, in Mastigomycotina, Zygomycotina, Ascomycotina, , 141-166, , Unit-7-General account, Habit, Structure and Methods of Reproduction, in Basiodiomycotina, Deuteromycotina and Mycoplasma, , 167-194, , Unit-8- Occurrence, General structure, Nutrition, Reproduction,, Economic and Ecological importance of Lichens, , 195-207, , BLOCK-3- PLANT PATHOLOGY, , PAGE NO., , Unit-9-Infection, Disease resistance and General Symptoms, , 209-230, , Unit-10-Symptoms, Morphology of the causal organism, Diseases, cycle and Control measures-I, , 231-246, , Unit-11-Symptoms, Morphology of the causal organism, Diseases, cycle and Control measures-II, , 247-260, , Unit-12-Plant Protection and Control measures of Plant Diseases, , 261-286, , UTTARAKHAND OPEN UNIVERSITY, , Page 5
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , BLOCK-1–GENERAL MICROBIOLOGY, , UTTARAKHAND OPEN UNIVERSITY, , Page 6
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-1-GENERAL ACCOUNT, DISTRIBUTION AND, CLASSIFICATION OF MICROORGANISMS AND, MAJOR MICROBES OF FOOD, WATER AND SOIL, 1.1- Objectives, 1.2- Introduction, 1.3-General account of microorganism, 1.4- Distribution, 1.5- Classification, 1.6-Major microbes of:, 1.6.1-Food, 1.6.2-Water, 1.6.3-Soil, 1.7- Summary, 1.8- Glossary, 1.9- Self assessment question, 1.10- References, 1.11- Suggested Readings, 1.12-Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 7
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 1.1 OBJECTIVES, Microbiology is the study of organisms invisible to our naked eye. This branch of science, explains the structure, nature, distribution, classification, occurrence, physiology, pathogenicity and application of microbes. This unit deals with the introduction, general, accounts, distribution, and classification of microbes and also about the soil, water and food, microbiology., After reading this unit one is able to:, Know about micro-organisms., Learn the variety of microorganisms which occur in the environment surrounding us., Understand the existence of minute organisms and realize that these microscopic, organisms are living and perpetuate themselves by reproduction., Discuss the distinct group of microbes which differ in form and other characters but, resemble with each other in their small size and simple structure., Study the systematic position, and distribution of micro organisms., , 1.2 INTRODUCTION, Microbiology is the study of organisms too small to be clearly seen by the unaided eye. Since, objects less than about one millimeter in diameter cannot be clearly seen and must be, examined with a microscope, such living objects are collectively referred as microorganisms, or microbes. Therefore microbiology is defined as the study of microorganisms. A variety of, organisms like bacteria, protozoa, viruses, fungi and algae are included in this category., Regarding the place of microorganisms in the living organisms, satisfactory criteria were, unavailable until late 1940, when more definite observation of internal cell structure was, made possible with the aid of the powerful magnification provided by electron microscope., Two cell types were discovered among these microorganisms. In some organisms the cells, contained nuclear substance which was not enclosed by a nuclear membrane, while in others,, a well-defined nucleus with a nuclear membrane was present. These two patterns were called, prokaryotic and eukaryotic respectively. According to these special features of, microorganisms, bacteria are prokaryotic and fungi, algae and protozoa are eukaryotic., Viruses are left out of this criteria as they are acellular organisms. Thus microbiology, includes five major branches namely, virology, bacteriology, phycology, mycology, and, protozoology., , UTTARAKHAND OPEN UNIVERSITY, , Page 8
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 1.3 GENERAL ACCOUNT OF MICROORGANISMS, Antony–van Leeuwenhoek (1632-1723) was the first who studied in detail the microbial, content of a variety of natural substances under the microscope. The various natural, substances studied by Leeuwenhoek were water from rain barrels, rivers, wells, sea, teeth, scrapings and naturally fermented material like vinegar. His observations were confirmed by, others, but only in nineteenth century, the extent and nature of microbial forms becames more, apparent., Microbes are either unicellular or multicellular or non- cellular forms. Protozoa, bacteria, and some algae and fungi are unicellular forms and are made up of single cells. While, most of the algae and fungi are multicellular forms. Viruses lack a cellular structure and, hence they are non-cellular particles and occupy a border line between living and nonliving things., Based upon the presence or absence of nuclear membrane, microbes are of two types, namely Prokaryotes and Eukaryotes. Prokaryotes have incipient nucleus which is, suspended in the cytoplasm. This includes bacteria., The microbes such as protozoa, algae and fungi are eukaryote which contain a nucleus,, with a nuclear membrane and is well separated from the cytoplasm., , General characteristics of Bacteria, 1) Bacteria are small microscopic and least differentiated microorganisms. These are, believed to be amongst the first primitive organisms on the earth possessing typical, prokaryotic cell organization., 2) They are omnipresent, i.e. found in all possible habitats., 3) They are unicellular and may live in association with others in colonies., 4) The size, shape and arrangement of bacterial cells vary and their size is about .5 micron to, 3 micron., 5) They exhibit a variety of shapes e.g., spheres (coccus), rods (bacillus), spirals (spirillum),, curved (vibrio) etc., , Fig.1.1. Different shapes of bacteria, , 6), , 7), 8), , They possess very rigid cell wall, which is not made up of cellulose, characteristic of, plant cell walls. It generally contains a peptidoglycan (murein), lipid and, lipopolysaccharides. The rigid cell wall determines the shape of bacterial cells., Nuclear material is not enclosed in a nuclear membrane. Nucleolus is absent., An extra chromosomal DNA called plasmid is usually present in the cytoplasm., , UTTARAKHAND OPEN UNIVERSITY, , Page 9
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.1.2. A bacterium showing appendages, , 9), , Cell organelles includes 70s type ribosome and mesosome formed by invagination of, plasma membrane.Otherorganelles such as mitochondria, lysosomes, Golgi body,, endoplasmic reticulum,centriole etc. are absent., , Fig.1.3.Structure of a typical bacterium (E. Coli), , 10) Appendages like flagella and pili are present. Some pili are longer in some bacteria and, are called as sex pili (Fig.1.2, 1.3)., Motility is brought about by flagella. The Bacilli and spirilla are motile and the cocci, are non-motile. Thus the bacteria may motile or non-motile., 11) When flagella are absent, the bacterium is called atrichous. In motile bacteria, the, number and position of flagella vary. The arrangement may be monotrichous (a single, polar flagellum), lophotrichous (a cluster of polar flagella), amphitrichous (Flagella at, both the ends either singly or in cluster), cephalotrichous (two or more flagella at one, end of the cell), peritrichous (cell surface evenly surrounded by several flagella), (Fig.1.4)., 12) The flagella are hair like or helical, consists of a single minute filament which is made, up of fibrils of flagellin protein. Unlike hair a flagellum grows at its tip rather than at, base., 13) Bacteria are either Gram positive or Gram Negative. Gram positive bacteria retain violet, colour on Gram staining while Gram negative bacteria appear in red colour. This is, because of the difference in their cell walls. The cell wall of gram positive bacteria, contains several layers of peptidoglycan in addition to techoic acid and low quantity of, lipoprotein and lipid. In gram negative bacteria, cell wall has thin layer of peptidoglycan, and high amount of lipo protein and lipid. Techoic acid is absent in these bacteria., , UTTARAKHAND OPEN UNIVERSITY, , Page 10
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 14) In some bacteria, shorter and thinner hair like appendages are present on the surface of, the cell wall. These structures are called pili or fimbrae. There function is to adhere the, cell to surfaces and sometimes help in transfer of genome to other bacterial cells. These, are called sex-pili., , Fig.1.4. Showing flagellation in bacteria, , 15) A bacterial cell is protected by a cell envelope made up of a capsule, a cell wall and a, plasma membrane. The bacteria covered by a capsule are called capsulated bacteria., While the bacteria which do not contain a capsule are called non- capsulated bacteria., 16) Bacteria may be heterotrophic or autotrophic, Heterotrophic may be parasitic,, saprophytic or symbiotic. For nutrition, autotrophs use CO2 as the source of carbon while, heterotrophs use organic substances as the source of carbon., 17) Based on temperature tolerance of bacteria they are of three types: Mesophilic bacteria grow well in temperature between 250C -400C., Thermophilic bacteria grow well above 400C., Psychrophilic bacteria grow well in temperature less than 250C., 18) On the basis of availability of O2 bacteria may be aerobic or anaerobic or facultative, anaerobic., Aerobic bacteria use oxygen for respiration., Anaerobic bacteria use CO2., Facultative anaerobes use oxygen when it is available and use CO2 when, oxygen is not available., 19) Bacteria reproduce by binary fission, budding, fragmentation, endospores, exospores and, conidiospores., 20) True sexual reproduction is lacking. However, genetic recombination occurs by, conjugation, transformation and transduction., , General Account of Algae, 1), 2), 3), , Algae are simple, chlorophyll bearing, and unicellular or multicellular microorganisms., Being chlorophyllous these are autotrophs., Algae are heterogeneous groups. They vary in size, habitat and reproductive processes., Algae are ubiquitous and abundantly present in sea water, fresh water, in damp soil, on, rocks, stones, barks of trees, on plants and animals., , UTTARAKHAND OPEN UNIVERSITY, , Page 11
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 4), 5), 6), 7), , 8), 9), , 10), , 11), , 12), 13), , BSCBO-101, , Plant body of algae is called thallus which does not show differentiation into root, stem,, leaf and true tissues., Algae are aquatic or terrestrial. But most of them are aquatic. They are either free living, or attached forms., A few algae are parasites. Some algae are of specialized habitats, e.g. parasites,, symbiotic cryophytes and thermophytes etc., Algae are unicellular like Chlamydomonasor multicellular like Spirogyra. Multicelluar, algae may be in the form of colonies like Volvox or in the form of filaments as, Spirogyra., The algae may be prokaryotes or eukaryotes. All blue green algae are prokaryotes., The cell consists of a cell wall, a plasma membrane, cytoplasm and nucleus. The, cytoplasm contains mitochondria, plastids, ribosomes, Golgi complex, endoplasmic, reticulum., The plastids in algae, contain pigments which are of three types –, (a) Chlorophylls: Five types chlorophyll (a, b, c, d and e) are found in different algae., Chlorophyll a is present in all the algae., (b) Carotenoids: These are the yellow and orange pigments (namely carotenes and, xanthophylls) and are found in varied quantities in different algae., (c) Biliproteins or phycobilins: These pigments include phycocyanin (blue in colour), and phycoerythrin (red in colour) and presence of these pigments is the, characteristic feature of certain types of algae., The pigments are present in chloroplasts, which are of different shapes in different, genera. The chloroplast contains one or more spherical bodies called pyrenoids which, are the centres of starch formation., Some algae are motile and possess flagella., Reproduction in algae is of three types, namely, vegetative, asexual and sexual., Vegetative reproduction takes place by fragmentation, fission, budding etc, asexual, reproduction by production of asexual spores (motile or non-motile). Asexual, reproduction is most common method of reproduction during favorable conditions., Algae reproduce sexually during unfavorable conditions by producing gametes., , General Account of Fungi, 1), 2), 3), 4), 5), 6), 7), 8), , Fungi are achlorophyllous, non-vascular eukaryotic thallophytes., They are non-green so heterotrophic microbes obtaining their food in a soluble form by, uptake through plasma membrane., Being heterotrophic, they live as parasites, saprophytes or symbionts., They are ubiquitous in distribution and occur in any habitat where life is possible., There are about 100,000 species of fungi., Plant body of fungi typically consists of branched filamentous hyphae which form a, network called mycelium. The hyphal structure is variously modified., The hyphae are aseptate, multinucleate in lower forms while septate and uni, bi or, multinucleate in higher forms., Protoplasm remains surrounded by a distinct cell wall made up of fungal cellulose, known as chitin. But in primitive slime moulds cell wall is absent., , UTTARAKHAND OPEN UNIVERSITY, , Page 12
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 9), , Fungi are entirely devoid of chlorophyll but carotenoids are normally present. Cytoplasm, contains endoplasmic reticulum, mitochondria, Golgi bodies and many non-living, substances like reserve food., 10) In lower fungi the reproductive cells (Asexual spores and gametes) are motile (uni or, biflagellate). But the higher fungi lack motile cells and show gradual reduction of, sexuality., 11) Flagella are two types (i) whiplash (acronematic) flagella are smooth and (2) Tinsel, (pentonematic) flagella with numerous minute hairs like structures on their surface., 12) Fungi are heterotrophic due to absence of chlorophyll. So they have to depend for their, food on others. Therefore they may beof the following types:, (a) Parasites obtain their nutrition from other living plants or animals. Some of them live only, on living protoplasm and are called obligate parasites. Whereas others can also grow on dead, organic matter in absence of living host and are known as facultative saprophytes., , (b) Saprophytes obtain their nutrition from the dead decaying organic matter. Among, these, some saprophytes such as Mucor can obtain their nutrition only from dead, organic matter and are known as obligate saprophytes. On the other hand some, saprophytic fungi as Fusarium have the capacity to invade living organisms and are, known as facultative parasites., (c) Symbionts grow on other living organisms and both are mutually benefited. Such, association is known as symbiosis, Lichens and mycorrhiza are common examples of, this, in which fungal partner shows mutualistic relationship with alga and roots of, higher plants respectively., 13) In unicellular fungi whole vegetative cell is transformed into a reproductive unit such, fungi are known as Holocarpic while in most of the fungi only a part of the vegetative, mycelium forms reproductive unit and rest remain vegetative. Such fungi are known as, Eucarpic., 14) Fungi reproduce by vegetative, asexual and sexual means. Vegetative by fragmentation, (e.g., Rhizopus, Alternaria etc.) fission (e.g., yeast) and budding (e.g. yeast and Ustilago), Asexual reproduction occurs during favourable condition by the formation of a variety of, conidia and spores. Spores may be unicellular (e.g. Aspergillus) or multicellular (e.g., Alternaria). They may be endogenous (developed inside in pycnia or sporangia) or, exogenous (developed outside on sporophores or conidiophores). Some common asexual, spores in lower fungi are motile known as zoospores. (e.g., Phytophthora), Non motile, known as aplanospores or conidia (e.g. Mucor, Rhizopus). In Higher fungi these nonmotilespores are called conidia, oidia or chlamydospores., 15) Except for the class Deuteromycetes, sexual reproduction occurs in all groups of fungi. It, is completed in three phases (a) Plasmogamy (fusion of protoplasm of two compatible, gametes of sex cells) (b) karyogamy (fusion of two nuclei from two gametes to form, Dikaryon). (c) Meiosis (after karyogamy reduction division takes place in diploid, nucleus to form haploid stage). The sex organs if present are called gamentangia which, may form gametes., 16) The various methods of sexual reproduction (by which the compatible nuclei are brought, together for plasmogamy) are as follows:, UTTARAKHAND OPEN UNIVERSITY, , Page 13
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (a) Planogametic copulation (fusion of two naked motile gametes) May be either, Isogamy (fusing gametes morphologically similar) or Anisogamy (fusing gametes are, both morphologically and physiologically dissimilar) or Oogamy (fusion between, female gamete (egg) and male gamete (antherozoid)., (b) Gametangial contact (Male and female gametangia come in close contact with the, help of a fertilization tube)., (c) Gametangial coupulation (Fusion of entire contents of two compatible gametangia), and formation of zygote which develops into a resting spore e.g., Mucor, Rhizopus., (d) Spermatization (sex organs are completely absent and the sexual process is, accomplished by minute spore like spermatia (malegamete) and specialized receptive, hyphae (female gamete) e.g., Puccinia., (e) Somatogamy (sex organs are not at all formed but two vegetative cells or two, vegetative hyphae take over the sexual function and fuse together). e.g., Morchella, and Agaricus., 17) The optimum temperature for the growth of fungi is between 200C to 300C., 18) Although light is not essential for growth, but for sporulation in many species, some, light is necessary., 19) There are five basic types of life cycles in fungi as asexual, haploid, haploid-dikaryotic,, haploid-diploid and diploid., , General Account of Viruses, 1), 2), 3), , 4), , 5), 6), , 7), , Viruses are exceptionally simple, filterable, obligate, intracellular particles capable of, reproducing inside a living host., These are extremely smaller in size (smaller than bacteria) and it ranges from 20 nm to, 300 nm in diameter., Inside a living, the viruses are active and they feed, reproduce, grow and move. But, when they live outside, they remain inactive and behave as non- living things. They are, also called living chemicals as they behave like chemicals and can be crystallized., Viruses differ fundamentally from cellular organisms in that they contain only one type, of nucleic acid either DNA or RNA. The nucleic acid may be single or double stranded, DNA or RNA and occur in either linear or circular form., Viruses do not contain cellular structures such as plasma membrane, mitochondria, Golgi, complex, lysosomes, ribosomes etc., Their basic structure consists of a protein coat, (capsid) and nucleic acid. The smallest, viruses known as virioids, consists of a single strand of naked nucleic acid without, protein coat. Capsid is made up of several identical protein subunits known as, capsomeres. These subunits are usually arranged in the helical or polyhedral geometric, forms which are specific for a particular virus., The capsomeres, forming the capsid (protein coat) of a virus, are of two types: -Pentamer, (made up of five identical monomers) and Hexamer(having six monomers). Each, monomer is connected with the neighbouring monomers on either side with the help of, bonds. Similarly capsomeres are also connected with each other but the bonds between, capsomeres are weaker., , UTTARAKHAND OPEN UNIVERSITY, , Page 14
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 8), , BSCBO-101, , In complex forms (e.g., influenza and herpes virus and many plant viruses) the virus, particles are surrounded by on outer envelope. The envelope is membranous and made, up of protein, lipids and carbohydrates. Viruses with envelope are called enveloped and, those without envelope are said to be naked (e.g., TMV) (Fig.1.5)., , Fig.1.5. Different structures in Viruses, , 9), , Viruses multiply by assembly line method. They do not divide. The cycle of, multiplication include :, attachment of virus to host cell., penetration by genetic material., production of virus components by the cell., assembly of new virus components by the cell., release from the host cell., 10) They lack enzymes for most metabolic processes., 11) Viruses are also unique microorganisms as they lack machinery for the synthesis of, proteins, 12) They are obligate intracellular parasites of animals, (protozoainsects,fish, birds,, amphibians, mammals and humans) or plants (angiosperms, gymnosperms, ferns, and, fungi)., 13) Many of the viruses have a close biological relationship with an arthropod or other type, of vector on which they are dependent for their transmission from one host to the other., 14) The viruses cause very serious diseases in crop plants, ornamental plants and forests, trees and many serious diseases in animals caused by viruses are well known since the, time immemorial., , UTTARAKHAND OPEN UNIVERSITY, , Page 15
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , General Account of Protozoa, 1), 2), 3), 4), , 5), , 6), , 7), , 8), , 9), , Protozoa are animal like organisms which are motile unicellular, non-photosynthetic, eukaryotic microorganisms., They normally obtain their food by ingesting other organisms by a process called, phagocytosis., These microorganisms are aquatic (fresh water or marine) or terrestrial (in soil) but, majority of them are parasites in other animals including humans., On the basis of the type of movement, the microorganisms are divided into there types:, (a) Amoeboid protozoa: flagella are absent but a temporary projection of part of, cytoplasm called pseudopodium is present., (b) Flagellate protozoa: They have either simple flagellum or a very complex flagellar, arrangement., (c) Ciliaryprotozoa: In some protozoa e.g. Paramecium, the surface is covered with these, structures and cilia are shorter than flagella and have a co-ordinate motion., The cell is made up of a plasma membrane, cytoplasm and nucleus. The plasma, membrane may have outer protective coverings such as pellicles, shell, test or torica.(Fig, 1.6)., The cytoplasm is more or less homogenous substance consisting of protein molecules. It, is made up of an outer ectoplasm and an inner endoplasm. Ectoplasm is gel like and, endoplasm is more voluminous and fluid., Some protozoa secrete a resistant covering and from a cyst at certain times of their life, cycle. This protects organisms against adverse environments. It also functions as a site, for nuclear organization and serves as a means of transmission in parasitic species., The nucleus is typical eukaryotic. It has nuclear membrane, nucleoplasm and, chromosomes. Normally only one nucleus is present (e.g.,Amoeba). But in some, protozoa two similar nuclei are found while in others e.g. ciliate species to dissimilar, nuclei (one micro and another macro nucleus) are found. The macro nucleus is large and, controls the metabolic activities and regeneration process and smaller or micro nucleus is, responsible for reproductive activity., On the basis of Nutrition the protozoa are autotrophic, holozoic or parasitic. Amoeba, uses pseudopodium for gathering food, Paramecium uses cilia, and Suctorianus, estentacles. The autotrophic forms have chlorophyll for photosynthesis. e.g., Euglena., Some protozoa show symbiotic relationship with other organisms., , UTTARAKHAND OPEN UNIVERSITY, , Page 16
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.1.6.Various forms of Protozoa, , 10) Asexual reproduction is some flagellate and ciliate species is associated with cyst, formation., 11) Reproduction takes place by asexual and sexual methods. Methods of asexual, reproduction are binary fission (e.g. Amoeba), multiple fission (e.g. Plasmodium), and, budding. Sexual reproduction takes place by conjugation (e.g. Paramecium). And, isogamy (e.g. Monocystis)., 12) Protozoa play an important role in food chain and food webs and are of particular, importance in the ecological balance of many communities. Some protozoa caused, diseases in animals including humans which are chronic and acute. In addition, these, microorganisms have also become important research tools for biologists and, biochemists., , 1.4, , DISTRIBUTION OF MICROORGANISM, , Microorganisms are cosmopolitan in distribution. They occur in every type of habitat that, can support life. This exceptional wide natural distribution is due to physiological diversity, exhibited by them. Following physiological characters contribute to their survival in varied, habitats:, (i) They can grow in inorganic environments without illumination. (Known as, chemolithotrophs)., (ii) They have the capacity for rapid growth., (iii) They have higher metabolic rates., (iv) They do not depend on the availability of specific micronutrients in the environment., UTTARAKHAND OPEN UNIVERSITY, , Page 17
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (v) Some of them (bacteria and cyanobacteria) can use nitrogen a capability not known to, occur in any other group., Under suitable environmental conditions, the microbes frequently grow multiply and produce, spores, cysts and resting cells. We shall discuss the distribution of microorganisms under, following heads:, 1. Microbes in soil, 2. Microbes in aquatic environment, 3. Microbes associated with plants, 4. Microbes in Air, 5. Microbes in Food, 6. Microbes in Milk., 7. Microbes of human body., , 1. Microbes in Soil, Man depends upon the soil for his food and the soil depends upon the micro-organisms for its, fertility. Agriculture would not be possible without microorganisms in the soil. There are five, major groups of microorganisms in the soil. They are Bacteria, Fungi, Algae, Protozoa and, viruses. One gram of soil has about 200-500 billions of microorganisms., , Microbial Population in a fertile soil, Type, Number per gram, Bacteria: Direct count,, 25 x 108, Dilution plate, 15 x 106, Actinomycetes, 7 x 105, Fungi, 4 x 105, Algae, 5 x 104, Protozoa, 3 x 104, A. Bacteria: Bacteria are the larger group of soil microorganisms. The bacteria which occur, in soil are coci, bacilli and spiral forms. Among these, the bacilli are in highest number and, they swim actively in the soil solution. Some common soil bacteria are the species of, Pseudomonas, Arthrobacter, Achromobacter, Bacillus, Clostridium, Micrococus,, Flavobacterium, Chromobacterium and Mycobacterium. Both autotrophic and heterotrophic, bacteria occur in the soil. Different species of Thiobacillus, Ferrobacillue, Nitrosomonas and, Nitrobacterare also found.in the soil as chemosynthetic autotrophic bacteria., Environmental factors like temperature, moisture, pH and depth of the soil affect the, distribution of bacteria in the soil. Certain bacteria like Mycobacterium and Pseudomonas are, commonly found in the soil near the petroleum wells. These bacteria are responsible for, oxidizing ethane. Escherichia bacteria seldom occur in the soil, many cellulolytic bacteria,, such as species of Cytophaga and Sporocytophaga are found in cellulose rich soil., , UTTARAKHAND OPEN UNIVERSITY, , Page 18
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , B. Actinomycetes: A large number of actinomycetes are present in dry and warm soil. They, are particularly abundant in the soil rich in decomposed organic materials. Species of, Streptomyces, Micromonospora and Nocardia are some common actinomycetes which occur, in soil. They are responsible for the characteristic musty or earthy smell of a freshly ploughed, field and are capable of degrading many complex chemical substances and thus play an, important role, in soil environment., C. Fungi: Several fungi are present in the soil and play an important role in the improvement, of soil nutrients in neutral and alkaline soils. Majority of soil fungi grow in acidic soils with, aerobic condition. Agricultural practices (crop rotation, use of fertilizers and insecticide etc.), and the depth of the soil also influence the fungal composition. Some important soil fungi are, the species of Aspergillus, Botrytis, Cephalosporium, Penicillium, Alternaria, Monilia,, Fusarium, Verticillium, Mucor, Rhizopus, Pythium, Chaetomium, and Rhizoctonia, Yeasts are, not very common in the soil except in Vineyard and orchard soils. Some fungi such as, species of Alternaria, Aspergillus, Cladosporim and Dematium are helpful in the preservation, of organic materials in the soil. Adding of organic matter to the soil stimulates soil fangal, flora. It is to be noted that the mycelium of fungi play an important role in binding the soil, particles because of their interwoven hyphae., Some phytopathogenic fungi also live in soil, often as saprophytes e.g. Spongospora, of myxomycetes that cause powdery scab of potato tuber; Phytophthora and Alternaria, species cause late blight of potato and early blight of potato respectively., D. Algae: The algae are widely distributed in the soil even in deserts. Many algae occur on, the surface of moist soils where sufficient light is available. The growth of algae is beneficial, for soil conservation and in improving soil structure. In paddy fields, blue green algae play a, significant role in nitrogen fixation., The most commonly occurring algae isolated from the soil are the members of, cyanophyceae and chlorophyceae e.g. Nostoc, Cylindrospermum, Anabaena and Chlorella,, Chlorococcus and Scytonema. In addition to these, certain diatoms are also frequently occur, in the soil., E. Protozoa: Protozoans are present in great abundance in the upper layer of the soil and, their number has a direct effect on bacterial population, because they ingest bacteria., Depending upon the condition of the soil, protozoans may exist in vegetative or cystform., Protozoans present in the soil belong to the class Mastigophora(species of Bodo, Cercobodo,, Cercomonas Monas, Spiromonasetc) class sarcodina(Amoeba, Biomyxa, Nuclearia, Trinema), and class ciliata are (Colpoda, Gastrostyla, oxytrichaetc)., F. Viruses: Viruses are present in very small number in the soil. Bacteriophages ingest, bacteria and actinomycetes and some viruses infect the fungi present in the soil., , 2. Microorganisms in aquatic environment, Water is unique environment for micro-organisms. A large number of micro-organisms are, carried from air and soil through various sources before water reaches reservoirs like rivers,, lakes, ocean etc. Aquatic habitats are only marginally aerobic. Microorganisms occurs in all, , UTTARAKHAND OPEN UNIVERSITY, , Page 19
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , depths. Drifting microbial life of aquatic environment is called Plankton. There are various, types of microorganisms in the aquatic environment .Some major examples are as follows:, I., , Bacteria: Bacteria are heterotrophic organisms of water, which may live in close, association with the algal flora of water. They develop well both in fresh and marine, water, near the submerged vegetation and just above the mud layer. Anaerobic bacteria, and few fungi also grow at the bottom sediments where are algae are absent. Pigmented, and non-pigmented bacteria like Pseudomonas, Chromobacterium, Achromobacter,, Flavobacterium and Micrococus occur frequently in unpolluted water Escherichia coli,, Streptococcus faecal is, Proteus vulgaris and Clostridium perfringens, the characteristic, intestinal tract inhabiting bacteria are also found in polluted water. Species of certain, bacteria like Pseudomonas vibrio, Favobacterium and Achromobacter may be present in, surface layers of sea water. These marine bacteria have important roles in nitrogen,, sulphur, Phosphorus and carbon cycles within the sea., II. Fungi: Certain fungi like Saprolegnia, Manoblepharis and Chytrids occur in well, aerated waters. These are saprophytes that grow on dead algae and small animals mainly, in fresh water habitats. They are important decomposers in aquatic environments. Some, water moulds are parasitic on the gills of fish. The fungi which occur in sea water, include the species of Chytridium, Patersonia and Ophiobolus., III. Algae: Many planktonic and benthic species of algae occur in different habitats of water, both fresh and marine. On the basis of their habitat in fresh and marine water, algae are, divided into following three categories:, (a) Epipelic Algae: Algae growing on deposit sediment in water. e.g.:- Oscillatoria,, Navicula., (b) Epipsammic Algae: Algae attached among the coatings of bacteria on sand grains., e.g. – Fragilaria, Chaetophora, etc. (Fresh water) and Raphoneis, Amphora, Rivularia, etc. (Marine forms), (c) Plankotonic Algae: Free floating algae. e.g., Anabaena, Pandorina, Chlamydomonas, etc. (Fresh water) and Rhizosolenia, Coratium, Chaetoceros, Peridiumetc (Marine, forms)., IV. Protozoa: The Protozoans are generally found in water films surrounding the soil, particles. Protozoans like Uroglenopsis, along with algae Eudorina and Volvox produce, an undesirable odour to water and pollute the fresh water ecosystem. Aquatic, protozoans, in planktonic forms are very commonly distributed in fresh and marine, water. These Protozoans are Ciliates, Flagellates and heliozoans etc., , 3. Micro-organism in Association with plants, Plant parts leaves, stems, flowers, fruits, seeds and roots are literally covered with microorganisms of various kinds. Some of the common associations of soil-micro organisms, with plant are –, (A), , Rhizosphere – Microbes influencing root and its surrounding. These are, (a), Legume Root Nodule e.g., Rhizobium, , UTTARAKHAND OPEN UNIVERSITY, , Page 20
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , (b), (B), , BSCBO-101, , Associative Nitrogen fixative. e.g., Azotobacter and Azospirillum., , Mycorrhizae- These are fungus- root association., , The roots of about 80% of all kinds of vascular plants are normally involved in symbiotic, association with mycorrhizae. Generally three types of mycorrhizal association have been, found:, I, , Ectomycorhizal: In this fungi grow as external sheath around the tip of the root with, limited inter cellular penetration of the fungus into the cortical region of root. This type, of association is common in oak, birch, beech and coniferous trees., , II, , Endomycorrhizal: In this, fungal hyphae penetrate the outer cortical cells of the plant, root where they grow intracellularly and form coils, swellings, or minute branches., These are characterized by two intracellular structures called Vesicles and arbuscules., That's why these are called vesicular – arbuscular mycorrhizae (VAM)., This is found in wheat, corn, beans, tomatoes, apples, oranges and many commercial, crops and grasses., , III Ectendomycorrhizal Association: This type of association has more persistant, Intracellular infections of cortical cells found predominantly in the family Orchidaceae., (C) Actinorrhizae: Actinomycete association with plant roots is called actinorrhizae., They are formed by the association of frankia strains. Frankia strains are capable of, nitrogen fixation and are important in the life of plants., (D) Tripartile Association: When a plant develops relationship with two different types, of micro-organisms it is called Tripartile association. Following types of associations, are examples of tripartite association:, (i), , Endomycorrhizae plus rhizobia including Rhizobium and Bradyrhizobium., , (ii), , Endomycorrhizae and actinorrhizae., , (iii), , Ectomycorrhizae and actinorrhizae., , (iv), , Ectendomycorrhizae and actinorrhizae., , 4. Microbes in Air, Air as a matter of fact, it not a suitable medium for the growth of the micro-organisms, and studies indicate that higher the altitude, one might expect to find fewer micro-organisms., Air itself does not support growth of the microorganisms but they are either borne on dust, particles, in moisture droplets expelled by men during talking, coughing and sneezing. Microorganisms are more numerous in the air during dry weather than in wet weather because rain, washes them out of the air., A variety of microorganisms are found in air over populated land areas. These include, spores of Bacillus and Clostridium, ascospores of Yeasts, Conidia of moulds, cysts of, protozoans, unicellular algae, Non spore forming bacteria (Micrococcus luteus), nonpathogenic bacteria, gram negative rods (Chromobacterium) etc. The spores of many, pathogenic fungi (e.g., rusts) causing crop diseases, plant pollens, seeds (minute) are, transmitted from one place of another through air currents., UTTARAKHAND OPEN UNIVERSITY, , Page 21
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , A number of human diseases are air borne and are transmitted by infectious dust e.g., Diphtheria(Corynebacteriumdiphtheria);Tuberculosis(Mycobacteriumtuberculosis),, whooping cough (Bordetella pertussis), children's influenza (Haemophilies influenzale) etc., , 5. Microorganisms in Food, Microbes are in direct competition with the human for the nutrients present in food. So foods, are ideal culture media for microbes, and different food items become contaminated with, microbes, which are present in soil, the bodies of plants and animals, water, air, equipments, during processing or preparation. Microorganisms that occur in foods may be divided into, following categories:I- Beneficial organisms which bring about desirable fermentations e.g., those which are, used in the preparation of cheese, vinegar etc., II- Harmful organisms which are responsible for decay of substances rich in organic matter,, and undesirable fermentations., III- Pathogenic organisms causing dreadful diseases and food poisoning by their toxic, secretions., IV- Microorganisms themselves form food e.g., single cell proteins and Mushrooms., The effect depends upon the type and numbers of microbes and also on the nature of food i.e.,, whether cooked, preserved or processed. Sometimes specific microbes are added to food to, get a desired effect. e.g., Poipickled cabbage (Lactobacillus plantarum)., Food rich in proteins (meat, eggs, etc.), those with carbohydrates (vegetables and fruits) are, spoiled by different types of micro-organisms by the process of putrefaction and, decomposition (e.g. Pseudomonas, Micrococcus and Bacillus)., , 6. Microbes in Milk, A number of micro-organisms thrive in milk (which is one of the nature's most, preferred food), and its products. Milk inside the udders is free from bacterial contamination,, but as it comes through the teat of the udder, it is contaminated as bacteria are always present, at the teat canals of the udder. Micrococci and streptococci constitute the teat microflora., Milk can be easily contaminated by pathogenic organisms to the milk in various ways., Since bacteria are present everywhere including hay, feeds and ground. The important direct, possible ways of contamination are –, (i) Milking utensils (ii) Hay and other feeds, (iii) Hands of milkers, (iv) The udder of cow and, buffalo and (v) the skin of animal. Various types of micro-organisms are found in milk. The, presence and absence of these organisms depend on sanitary quality and conditions of, production. The important microorganisms in milk are:, I., , Bacteria: Bacteria form the major section of microbes that grow well in milk. They may, produce beneficial or desirable effects and detrimental or undesirable effects. The study, of these bacteria in relation to milk and milk products is known as dairy bacteriology., , UTTARAKHAND OPEN UNIVERSITY, , Page 22
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (a) Beneficial Effects, Microorganisms are deliberately added to milk to produce fermented milk products, to, create new pleasing food flavours and odours. Yogurt is produced by adding two, bacteria: Streptococcus thermophilus and Lactobacillus bulgaricus in the ratio of 1:1., Streptococcus produces acid and Lactobacillus produce aroma components. Cheese,, which has been thought to be developed 5000 B.C. is one of the oldest human foods., About 2000 varieties of cheese are produced all over the world. Cheeses are classified on, the basis of texture or hardness as:Cheese, Bacteria Used, I. Softcheese, Streptococcus lactis and, (ripened), S.cremoris, II. Soft cheese Streptococcus lactis, (unripened), S. cremoris, S. thermophilus, Lactobacillus bulgaricus, III Semi soft, Streptococcus lactis and Brevibacteriumlineus, S. cremoris, IV. Hard, S. lactis, S.cremoris and Lactobacilluscasei, S.durans, S. thermophilus, V. Very Hard, S. lactis, S. cremoris, S. tshermophilusand, Lactobacillus bulgaricus, , (b) Detrimental or undesirable Effect, Spoilage occurs when microorganisms degrade the carbohydrates, proteins and fats of, milk. Examples of common types of spoilage in dairy products and associated bacteria are, following:Spoilage type, Bacteria involved, Souring, Lactobacillus sp. and Streptococcus sp., Sweet curdling Bacillus sp., Proteus sp., Micrococcus sp., Gas production Clostridium sp. and coliform bacteira, Red rot, Serratiasp., Grey rot, Clostridiumsp., II, , Yeasts: They are found in milk and milk products. They act on lactose and produce acid, and carbon dioxide. Some produce gassy fermentation and some are lipolytic in action., These contaminate milk through feed and soil. e.g.,Torulacremoris, Torulalactis., , III. Moulds: They contaminate and grow in large number on the surface of butter, cream,, khoa and cheese. The colour may be black, grey, blue or white. They produce, undesirable odour also. Some are lipolytic and some are proteolytic e.g. Penicillium sp,, Cladosporium and Gleotrichum., , UTTARAKHAND OPEN UNIVERSITY, , Page 23
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , IV Bacteriophages: Bacteriophages present in milk kill the bacteria in the starters and, interfere in the process of fermentation which is essential to produce certain milk, products such as butter and cheese., V, , Viruses and Protozoa: These are not common organisms present in milk products but, they occur in some rare conditions., , 7. Microbes of Human body, The human foetus in uterus is free from bacteria and other microorganisms. Within, hours after birth, it begins to acquire a normal microbiota within the first week or two. After, that a variety of microorganisms become associated with the human body. Thousands of, microbes are present around us and many inhabit human body in natural course. Most of the, microbes of the human body are commensals, as they do not harm the host. They obtain their, nourishment from secretion and excretory wastes of the human body. Some microbes act as, scavengers by ingesting excretory wastes or are beneficial to the host. e.g., – certain intestinal, bacteria synthesize vitamin E and K, whereas others protect the host from the pathogenic, microbes., I. Microbes of skin, The human skin always remains in contact with bacteria present in the air, but most of, them are unable to grow since the skin secretes some bactericidal substances.Staphylococcus,, Streptococcus, Propioni bacterium, moulds, yeasts and some pathogenic bacteria live on the, surface of the skin. Some dermatophytic fungi viz. Epidermophyton, Microsporum and, Trichophyton may colonize in the skin and produce athlete's foot and ringworm diseases., II. Microbes of the mouth cavity, Continuous presence of soluble nutrients and abundance of moisture in the mouth, cavity provides a suitable environment for the growth of microorganisms. Some common, microbes are Staphylococcus aureus, S. epidermidis, S. mitis, Lactobacilli, Actinomycetes,, Bacteroidesoralis, Candida albicans, Treponemadenticala, Mycobacteria, Entamoeba sp., and Trichomonasetc., III. Microbes of Gastro – Intestinal tract, Several micro-organisms such as staphylococcus aureus, S. epidermidis, Haemophilus, influenzae and Neisseria inhabit the pharynx. Stomach contains very few microorganisms, because of its acidic pH. When the stomach functions normally, it is devoid of microbes due, to the presence of gastric juices. Many gram + ve facultative bacteria and fungus Candida, albicansare found in the duodenum. Similarly a large number of micro-organisms are found, in the large intestine (colon). They include gram (-)ve bacilli gram (+)vebacilli,, Enterobacter, Escherichia coli, Proteus and Candida albicans. In addition to these certain, Protozoans Trichomonashominis, Entamoeba hartmsanni, are also present., , UTTARAKHAND OPEN UNIVERSITY, , Page 24
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , IV. Microbes of the mucous membrane of the eye, Staphylococcus albus, Comybacterium xerosis and mycoplasmas are usually, associated with the mucous membrane of the eye., V. Microbes in Respiratory tract, We inhale a large number of adsorbed micro-organisms along with dust- particles., Most of them are trapped in the nasal cavity. Some Staphylococci, aerobic Corynebacteria,, besides other cocciand bacilli inhabit the nasal cavity., VI. Microbes of Genito-urinarytract, The upper genitourinary tract consisting of kidneys, ureters and urinary bladder is, usually free of microorganisms. In both male and female, a few bacteria as Staphylococcus, epidermidis, Streptococcus faecalis and Corynebacterium sp. are usually present in the distal, portion of urethra. In the adult female genital tract, the major microorganisms are the acid, tolerant Lactobacillus sp., Bacteroides sp., aerobic corynebacteria, Peptostreptococus sp. and, Enterococci, Mycobacterium smegmatis and mycoplasmas., , 1.5 CLASSIFICATION, In the early 19th century the traditional classification of living organisms was given by, Aristotle. He classified the living organisms into two kingdoms Plantae and Animalia., Plantae includes algae, fungi and Bacteria & other plants. Other kingdom Animalia includes, all animals including protozoa., A three kingdom classification was given by E. Haeckel in 1866. Heincludeda the, third kingdom Protista and classified living organisms as follows:, 1- Protista (Algae, fungi, bacteria and Protozoa), 2- Plantae (excluding unicellular algae and fungi), 3- Animalia (excluding protozoa.), Later, Copeland (1956) suggested a four kingdom system of classification of living, organisms. He placed bacteria and blue-green algae in the fourth Kingdom Monera and fungi, in the third kingdom Protista., Whittaker in 1969 proposed a five kingdom system of classification of living, organisms. His classification is as follows:, 12345-, , Monera (Bacteria and Cyanobacteria), Protista (unicellular algae, slime molds and protozoa), Fungi, Plantae (Eukaryotic multicellular plants), Animalia (excluding protozoa), , Hawker and Linton in 1971 classified microorganisms into 3 heads:, I. Viruses: Specific group of sub-cellular obligate parasites., UTTARAKHAND OPEN UNIVERSITY, , Page 25
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , II. Prokaryote: organisms with prokaryotic organization. This included(a) Bacteria (unicellular forms without a definite nucleus)., (b) Higher Bacteria (filamentous actinomycetes to filterable mycoplasmas)., (c) Rickettsiae (Parasitic bacteria having the appearance of tiny rod shaped or spherical, resembling bacteria and viruses)., (d) Cyanobacteria (photosynthetic forms of prokaryotic organization), III. Eukaryote : organisms with eukaryotic organization which includes(a) Algae (unicellular eukaryotic algae belonging to Chlorophyceae, Chrysophyceae and, Euglenophyceae)., (b) Fungi (moulds) (fungi with unicellular to multicellular hyphae with cottony growth, belongs to Phycomycetes, Ascomycetes, Basidiomycetes, and deuteromycetes)., (c) Slime moulds (organisms with slimy mass of naked motile protoplasm called, plasmodium)., (d) Protozoa (unicellular animals without chlorophyll. and are divided into sarcodina,, sporozoa, ciliophora and mastigophora., (e) Nematodes (multicellular thread like cylindrical worms)., Recently microorganisms are classified into two major groups:, (A) Acellular Infectious agents, (B) Cellular Infectious agents, (A) Acellular Microorganisms: These are called acellular organisms as they do not possess, three minimum characteristics of a cell- Presence of a membrane, genetic material and, metabolic machinery., These are of following types:, I., , Viruses: Ultramicroscopic obligate parasites made up of nucleic acid, lack cytoplasm, and cell organelles and multiply only within the living host cell., A Provisional committee or Nomenclature of viruses (P.C.N.V.), headed by system proposed, by Lwoff, Horne and Tournier (1962). According this system all viruses are grouped into a, single phylum –Vira which is divided into subphyla, classes, orders, suborders and families., On the basis of following characters:, (a) Type of nucleic acid DNA or RNA., (b) Symmetric helical Cuboidal or biral., (c) Presence or absence of envelope around capsid., (d) Diameter of helical nucleo capsids and no. of capsomeres present in cuboidal viruses., , UTTARAKHAND OPEN UNIVERSITY, , Page 26
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , II, , BSCBO-101, , Viroids:, These are small naked RNA molecules. These were first discovered by Diener (1971)., They replicate autonomously. Viroid RNA is usually single stranded, circular and is of, very low molecular weight viroids cause various plant disease such as potato spindle, tuber (by PSTV), citrus exocortis, chrysanthemum stunt, cucumber pale fruit etc., , III Prions: These are rod-shaped proteinaceous infectious particles without nucleic acid;, Prions were named by S.B. Prusiner (1984) who was awarded Nobel Prize in Medicine, in 1997. Prions cause a variety of mammalian neurodegenerative diseases. These are, generally fatal and are referred to as transmissible spongiform encephalopathies, (TSES).These include diseases like scraple, disease of sheep; CreutzfeldtJakob disease, (CJD) and Kuru – Human diseases. Prions also cause madcow disease of bovino, spongiform encephalopathy (BSE)., IV Virusoides: They are also called satellite RNA. They are encapsulated by plant viruses, packaged together with a viral genome. They cannot replicate independently and do so, with the help of an associated virus., (B) Cellular Micro-organisms: These microorganisms are cellular as their cells possess a, membrane, genetic material and metabolic machinery. These are two types on the basis, of presence or absence of nuclear membrane., UTTARAKHAND OPEN UNIVERSITY, , Page 27
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 1. Prokaryotic microbes & 2. Eukaryotic microbes., , 1. Prokaryotic microbes, These are unicellular microorganisms. These show prokaryotic cell organization., Prokaryotic micro-organisms are again subdivided into two(A) Archebacteria, &, (B) Eubacteria, (A), Archebacteria: These are the primitive type of bacteria which lack muramic acid in, their cell walls; the membrane lipids have ether linked aliphatic branched chains. These, possess distinctive RNA polymerase enzymes. Their ribosome is also of different, composition in shape. These bacteria are categorized into (a) methanogenic bacteria (b), extreme halophiles and (c) thermoacidophiles., (B), Eubacteria (True bacteria):This comprises a vast majority of bacteria. The, Peptidoglycan cell wall contains muramic acid. The membrane lipids have ester linked, straight chained fatty acids., These are divided into following groups –, (i) Spirochetes: These are gram-negative, chemohetrotrophic bacteria, and are distinguished, by their structure and motility. They lack external rotating flagella but still can move through, very viscous solutions, exhibiting creeping or crawling movement when in contact with a, solid surface. Their unique style of motility is due to the presence of an axial filament. Two, or more than a hundred prokaryotic flagella called periplasmic flagella, extend from both, ends of the cyinder and often overlap one another. Spirochetes are anaerobic, facultatively, anaerobic or aerobic. Some pathogenic forms are: Treponemapallidum, Borrelia burgdorferi,, Leptospira and causing syphilis, lyme disease and Leptospirosis respectively., , (ii) Rickettsias: These belong to order Rickettsiales. These are a group of Gram-negative, intracellular parasitic bacteria. These resemble viruses in their very small size and, intracellular existence. They differ from viruses in having both DNA and RNA, a plasma, membrane, ribosome, enzymes etc. They are intermediate between bacteria and viruses., Some of the important pathogenic forms are:, Rickettsia prowazeki causes typhus fever;, Rickettsia rickettsii causes rockey mountain spotted fever;, Rickettsia orientalis causes scrub typhus; and, Rickettsia burnetti causes Q fever, (iii) Mycoplasma (Mollecutes), Mycoplasmas are prokaryotes without cell wall and are placed in the class molecules, (Mollis = Soft; cutis = skin). They are pleomorphic and occur in any shape such as spherical,, pear shaped, branched and helical filaments. They are non-motile but can glide along liquid, covered surfaces. They are usually facultative anaerobes but a few are obligate anaerobes., Their genome is one of the smallest (about 5-10 x 108daltons) found in prokaryotes. They live, , UTTARAKHAND OPEN UNIVERSITY, , Page 28
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , as saprophytes or parasites or pathogens of plants, animals, man or insects. The common, examples of mycoplasmaare:, Mycoplasma pneumoniae (causing mycoplasmal pneumonia); Mycoplasmamycoides, and gallisepticum causing contagious bovine pleuropneumonid in cattles, and in chicken, respectively. Mycoplasma urealyticum causes genital infection., (iv)Cyanobacteria (Blue green algae), Cyanobacteria are blue green algae or blue green bacteria. They form a connecting, link between bacteria and green plants. They are prokaryotic. They are photoautotrophs as, they contain chlorophyll which is located in thyllakoids. Their photosynthetic system closely, resembles that of eukaryotes, because they possess phycobili proteins as accessory pigments, like red algae. Cyanobacteria vary greatly in shape and appearance. They may be unicellular, and exists in colonies of various shapes or multicellular and form filaments called trichomes., Cyanobacteria are not toxic to man. The cytoplasm contains phycobillins and, carboxysomes. They have heterocysts which are specialized cells for nitrogen fixation and, akinetes for spore formation. Common examples are: Anabaena, Nostoc, Chlorococcus,, Oscillatoria, Stigonemaetc., (V) Actinomycetes:, Actinomycetes include fungus like bacteria. (Actis = rays; mykes = fungus), These are aerobic, gram positive bacteria that form branching usually non-fragmenting, hyphae and bear asexual spores. Most actinomycetes are non-motile. Motility is confined to, flagellated spores only. They are mainly soil inhabitants and can degrade a variety of organic, compounds., Actinomycetes are chemoorganotrophs, as they rely on organic compound for their, energy. These organisms are of great economic importance as they produce about 85% of, know antibiotics., The important actinomycetes are the following: Streptomyces(produces, streptomycin): Erythromycine & Chloramphenical, tetracycline; Micromonospora(produces, gentamycin) .Some actinomycetes fix atmospheric nitrogen and live symbiotically (e.g., Frankiasp). A few actinomycets are pathogens of human, animals and plants e.g., Thermoactinomyces vulgaris whichcauses a respiratory disease called Farmer‘s lung in, humans., , 2. Eukaryotic Microbes, These are they microorganism with eukaryotic organization. Such organisms are, divided into three parts: I Unicellular Eukaryotic Microbes, II Multicellular Eukaryotic, Microbes (Fungi) & III Helminthes., I. Unicellular Eukaryotic Microbes, These are solitary or colonial unicellular microbes with eukaryotic organization., They are usually aerobic forms, and can be motile or non- motile. Motility is due to cilia,, flagella or pseudopodia. They are subdivided into following types:, UTTARAKHAND OPEN UNIVERSITY, , Page 29
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (a) Photosynthetic Protists (Unicellular algae) :, It includes unicellular photo synthetic organisms belonging to different groups, Chlorophyceae,, Euglenophyceae, Xanthophyceae, Pyrrophyceae, Bacillariophyceae, and Chrysophyceae. Some major group of this are, 1-, , 2-, , 3-, , Dianoflagellates: These belong to Chrysophyceae. They are unicellular with cellulose, cell wall. They possess two flagella. They reproduce only asexually. Sexual reproduction, is unknown. Some of them e.g. Gonyaulaxsecretes a toxin which kills marine animals, like fish known as 'red tide'. Some Dianoflagellates are phosphorescent and make the sea, Scarface glow in the dark., Diatoms: These belong to bacillariophyceae. They lack flagella. Diatoms are diploid and, reproduce asexually as well as sexually. Diatoms are nearly indestructible because of, deposition of silica in their cell walls. They leave behind large amounts of cell wall, deposits called diatomaceous earth., Euglenoids: These are Euglena like protists. They lead plant like and animal like lives., These are free living forms found in fresh water ponds and ditches on damp soil. They, do not possess a cell wall. The flagellum is duplicated before the cell divides. e.g., Euglena., , (b)Consumer – Decomposer protists:, These resemble fungi in appearance and life style but are more closely related to, protists in cellular organization, reproduction and life cycle. These include:, I. Acellular Slime moulds (Myxomycota), They are wall less mass of multinucleate protoplasm e.g. Physarum. It slowly streams, or glides over decaying leaves or logs. This strand of protoplasm is called plasmodium., Feeding is by phagocytosis., II. Cellular Slime moulds(Acrasiomycota), These are numerous individual amoeboid cells which aggregate together and move like a, mass of protoplasm. The individual cells are not fused. This is called pseudo plasmodium., e.g.Dictyostelium., III. Water mould (Oomycota):, They consist of finely branched filaments called hyphae. Their cell walls are made up, of glucanc and cellulose. Very small amount of chitin is found in rare cases They reproduce, sexually by a large egg cell and a small antheridium, asexual reproduction by biflagellate, zoospores. They are saprophytes (e.g. Saprolegnia) or parasites (e.g. Phytophthora infestans)., Another significant feature of this group is presence of hydroxyproline amino acid in the wall, protein., (c) Protozoan Protists:, Protozoa are animal like protists that can be defined as motile eukaryotic unicellular, microorganisms. They resemble multicellular animals in their morphology and physiology., UTTARAKHAND OPEN UNIVERSITY, , Page 30
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Some of them secrete a resistant Covering and form cyst which protects organisms against, adverse environments. These organisms move by pseudopodium, flagella or cilia, and, reproduce asexually and sexually. They play an important role in food chains and food webs., Many of them are parasitic in humans and animals., , I. Multicellular Eukaryotic Fungi:, This group includes the organisms which are placed in the kingdom fungi by, Whittaker. They exist primarily in the form of filamentous hyphae. They lack chlorophyll,, and reproduce asexually, sexually or by both methods. They are important decomposers and, play an important role in recycling of minerals, thus are of great importance to humans in, both beneficial and harmful ways. They are further divided into four groups (1), Phycomycetes (2) Ascomycetes (3) Basidiomycetes and (4) Deuteromycetes., (3). Helminthes:, The kingdom Animalia has only one group of microscopic organisms, the helminthes. Tape worm, flukes and round worms are collectively called helminthes., There are two types of parasitic helminthes based upon morphological form. They are the, flatworms, belonging to phylum Platyhelminthes with a very thin segmented body and round, worms belonging to phylum Aschelminthes with an elongate, cylindrical, unsegmented body, plan., All helminthes are multicellular animals. They absorb nutrients through their body, wall while living in the host intestine; most worms complete their life cycle on two hosts, and, have the capacity to regenerate. Some pathogenic helminthes are: Ascarislumbricoides, (Round worm); Necatoramericanus (Hook worm); Fasciola hepatica (Sheep liver fluke);, Taeniasolium (Pork tape worm) and Taeniasaginata (Beef tap worm) etc., , 1.6 MAJOR MICROBES, 1.6.1 Major Microbes of food, Food is an indispensable item for all living organisms. All food items are associated, with microbes in one form or other. Even naturally occurring food such as fruits and, vegetables contain microorganisms. Major microbial flora of common food are listed below:, , Types of food, , Microbial flora, , UTTARAKHAND OPEN UNIVERSITY, , Page 31
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Disease, , Microbe, , Food involved, , Food poisoning, , Bacillus cereus, , Botulism, , Clostridium botulinum, , Perfringens food poisoning, , Clostridium perfringens, Staphylococuus aureus, , Meats, potatoes, Cereals., Rice products, pudding., Fish, meats and low acid, canned food., Animal and Poultry Products., Meat,, dairy, Products,, Poultry, custard and starch, containing food., , Staphylococcal food Poisoning, , (B) Major Food inflations, Campylobacteriosis, , Campylobacter jejuni, , Listeriosis, , Listeria monocytogenes, , Salmonellosis, , Salmonella typhimurium, , Shigellosis, , Shigellasonnei, S. flexneri, , Yersiniosis, , Yersinia enterocalitica, , E.coli enteritis, , Cheese and raw vegetable, , Raw milk, raw chicken and, poultry products., Poorly, processed, dairy, products., Poultry, eggs, dairy products,, meat., Insanitary cooked food, fish,, potatoes and salads., Milk and meat product., , 1.6.2 Major Microbes of Water, Water is unique physical environment, andfavours the existence of many types of, micro organisms that are not common in soil. Micro organisms occur in all depths. The, surface film and bottom sediments have a high concentration of microorganisms. Drifting, microbial life of aquatic environment is called plankton, composed of phytoplankton and, Zooplankton. The bottom region of the body of water harbours largest number and kinds of, microorganisms called benthic microorganisms. The movement of water by wind, tide and, currents affect the distribution of microorganisms., (a) Major microbes of Ponds and Lakes, Lakes and ponds of temperate region show thermal stratification which influences the, microbial population in different seasons. Common fresh water micro organisms are, Pseudomonas, flavobacterium, Aeromonas, and Acaligenes, Clostridium, Thiothrix, and Thiobacillus. Besides this both, Cyanobacteria and many algae contribute to, massive water blooms., (b) Major Microbes of sea, Diatoms, Cyanobacteria, Silicoflaellates, Dinoflagellates,etc.Chlamydomonas are, major phytoplanktons. Many microorganisms, particularly algae and cyanobacteria, cause a condition called Red sea and Red tides.Brown, amber or greenish yellow, colourationis also due to abundance of micro organisms., , UTTARAKHAND OPEN UNIVERSITY, , Page 33
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , , , , , , , BSCBO-101, , Microbes are widely distributed and are omnipresent. Theycan be isolated from air, water,, soil, in living plants and animals and dead organic substanses., Microbes areeitherUnicellularormulticellularornon cellular forms, and are prokaryotes or, eukaryotes., Microorganisms include viruses, Bacteria, Algae, Fungi and Protozoa. Non cellular, microbes are viruses. Unicellular microbes have single cells e.g., Protozoa, Bacteria,, someAlgae and some fungi. Multicellular microbes have many cells e.g., FungiandAlgae., Microbes have the capacity for rapid growth. They do not depend on the availability of, specific micronutrients in theenvironment., Some of the microbes (bacteria and cyanobacteria) can fixatmosphericnitrogen., Soil is an excellent natural medium formicroorganisms. Man depends upon the soil for his, food. The soil depends uponthemicro organisms for its fertility., Food is an indispensable item for alllivingmicro organisms. All food items are, associatedwithmicroorganismsinoneform or other., In aquatic environment micro organisms occur from water surface to greater depths. The, various water sources as ponds, pools, Lakes, rivers and oceans show a great diversity in, theirmicroflora., , 1.8 GLOSSARY, Actinomycetes: Gram Positive Bacteria that are characterized by the formation of branching, filaments., Adenoviruses: A group of DNA viruses, causing infection of the upper respiratory tract., Antibiotic: A substance of microbial origin that has antimicrobial activity and it kills the, other micrograms., Archaebacteria: A group of bacteria that includes primitive type of bacteria in which cell, wall lack muramic acid., Bacillus: A rod shaped bacterium., Bacteriophage: A virus whose host is a bacterium and replicates within bacterial cell., Biofertilizers: The nutrients of biological origin added to the soil to enrich the soil fertility, are called biofertilizers., Botulism: A neuroparalytic disease due to an exotoxin produced by the bacterium, clostridium botulinum in improperly canned or preserved food., Chemoorganotraphs: organisms relying on organic compounds for their energy source., Ectomycorrhiza: Amycorrhiza in which the fungal hyphae grow only intercellularly, never, entering the cell wall of the host cell., Endomycorrhiza: Amycorrhiza in which the fungal hyphae penetrate the cell wall of the, host cell., Epipelic Algae: Algae growing on deposit sediment in water., Epipsammic Algae: Algae attached among the coatings of bacteria on sand., Eubacteria: True bacteria in which cell wall contain muramic acid., Mycorrhiza: A symbiotic association between fungus and plant roots., Prions: Proteinaceous rod shaped infectious particles without nucleic acid., UTTARAKHAND OPEN UNIVERSITY, , Page 37
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Symbionts: Two organisms living together with mutual benefits., VAM: Vesicular Arbuscular Mycorrhizal fungi. These are also called endomycorrhiza., Virioids: Small naked RNA molecule., Yoghurt: Fermented liquor made from milk., , 1.9, , SELF ASSESSMENT QUESTIONS, , 1.9.1 Choose the correct answer from the given below:, (a) Which one of the following isarchaebacteria?, (i) Blue– green, (ii) Rickettsias, (iii) green sulphar, (iv) Methanogens, (b)Which of the following water is free from bacteria?, (i) deep well water, (ii) sea water, (iii) Water of hot spring, (iv) rain water as it falls down, (c) Bacteria which in association with legume roots fix atmospheric nitrogen are called:, (i)Azobacter, (iii)Rhizobium, , (ii) Paseudomonas, (iv) E.coli, , 1.9.2 Fill in the blanks:, a), , The Characteristic earthy smell of freshly ploughed field is due to a compound, , called ................ produced by streptomyces., b), , Actinomycete association with plant root is called................., , c), , Botulism is caused by........................., , 1.9.3 Answer the following in one word or in one sentence., a) Name the microorganism which causes red rot of milk., b) Name a symbiotic bacterium., c) What name is given to a virus which infects bacteria?, 1.9.4 Write true or false (T/F)., a) Prions are single stranded RNA containing cellular infections agents., b) Flagellated cells are absent in cyanobacteria., c) Viruses contain both RNA and DNA., 1.9.5 Explain the following –, i), , Associative nitrogen fixation., , ii), , How do microorganisms contribute to body odour?, , iii), , Compare prokaryotic and eukaryotic microorganisms., , UTTARAKHAND OPEN UNIVERSITY, , Page 38
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Answers Keys:, 1.9.1- (a)-(iv), (b)-(iv), (c)-(iii), 1.9.2- (a)-Geosmin, (b)-Actinorrhizae, (c)- Clostridium botulinum, 1.9.3-(a)-Serratiamarcescens, (b)-Rhizobium, (c)- Bacteriophage, 1.9.4-(a)-False, (b)- True, (c)- False, , 1.10 REFERENCES, , , , , , , , , , , , , , , , , Atlas, R.M. Principle of Microbiology., Bhagat Singh and Renu Singh, 2011. Microbiology for Medical Sciences. I.K., International Publishing House Pvt. Ltd. New Delhi., Casida, L.E. 1968, Industrial Microbiology, John Wiley and sons, New York., Clifton, A. 1958, Introduction to the Bacteria, MC Graw, Hill Book Co. New York., Doelle, H.W. and C.G., Heden 1986. Applied Microbiology, Kluwer Academic Press,, London., Dubey, R.C. & D.K. Maheshwari. A text book of Microbiology. S.Chand& Co. New, Delhi., Frazier, W.C. & D.C. Westhoff. 1988. Food Microbiology. Tata McGraw Hill., Kaushik, P. 1996, Introductory Microbiology. Emkay Publ. Delhi., Mandahar, C.L. 1978, Introduction to Plant viruses. S. Chand & Co. Ltd., Delhi., Mukherjee, K.G., and Ved Pal Singh, 1997. Frontiers in Applied Microbiology, Rastogi, Publ. Meerut., Norris, J.R. and D.W. Ribbons 1970. Methods in Microbiology. Academic Press, London., Pelezar, M.J. Chan, ECS and Kreig, N.R. 1993, Microbiology, concept and Applications., M.C. Graw Hill, New York., Power, C.B. and H.F. Daginawala, 1970. Methods in Applied Microbiology, Rastogi, Publ. Meerut., Prescott, I. J., J.P.M. Harley & A.D. Klein, Microbiology. Tata MC Graw Hill., Robinson, R.K., 1990. Dairy Microbiology, Elsevier Applied Sciences, London., , 1.11 SUGGESTED READINGS, , , , , , , Ananthanarayan&Panicker, 1997. Text Book of Microbiology Orient Longman., Bhagat Singh and Renu Singh, 2011.Microbiology for Medical Sciences I.K., International Publishing House Pvt. Ltd. New Delhi., Dubey, R.C. & D.K. Maheshwari. A Text Book of Microbiology. S. Chand & Co. Delhi., Kaushik, P. 1996. Introductory Microbiology.Emkay Publ. Delhi., Mandahar, C.L. 1978. Introduction to Plant viruses. S. Chand & Co. Ltd., Delhi., , UTTARAKHAND OPEN UNIVERSITY, , Page 39
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , BSCBO-101, , Subbarao, N.S. 1994. Soil Micro organisms& Plant Growth. Oxford & IBH Pvt. Ltd., New Delhi., , 1.12 TERMINAL QUESTIONS, 1., , Give a brief account of Salient features of main groups of microorganisms., , 2., , Write short notes on the following:, (i) Archebacteria, , (ii) Viroids and Prions (iii) Mycoplasma, , (iv) Cyanobacteria, , (v) Actinomycetes, , (vi) Spirochete., , 3., , Discuss the different approaches to classification of microorganisms., , 4., , What are the applications of the following microorganisms?, (a) Rhizobium, , (b) Bacillusthuringiensis, , 5., , List various types of microbial food spoilage and name the organisms, responsible in each instance., , 6., , Discuss the distribution of microorganisms in soil., , 7., , Differentiate the following:, (i), , Prokaryotes and Eukaryotes, , (ii), , Ectomycorrhiza and Endomycorrhiza, , (iii), , Autotrophs and Heterotrophs, , (iv), , Archaebacteria and Eubacteria, , UTTARAKHAND OPEN UNIVERSITY, , Page 40
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT 2- ISOLATION AND CULTIVATION OF, MICROORGANISMS, INSTRUMENTS USED IN, MICROBIOLOGICAL STUDIES, 2.1-, , Objectives, , 2.2-, , Introduction, , 2.3-, , Sterilization, , 2.4-, , Preparation of culture Media, , 2.5-, , Dispensingthe medium, , 2.6-, , Some important culturemedia, , 2. 7-, , Methods of obtaining pure cultures., , 2.8-, , Methods of isolation, , 2.9-, , Cultivation of viruses, , 2.10- Culture techniques, 2.11- Instruments used in microbiological studies., 2.12- Summary., 2.13- Glossary, 2.14- Self assessment questions., 2.15- References, 2.16- Suggested Readings, 2.17, , Terminal Questions., , UTTARAKHAND OPEN UNIVERSITY, , Page 41
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 2.1, , BSCBO-101, , OBJECTIVES, , It is well known that microorganisms occur in natural environments; and are, contaminated and mixed with several other forms of life. To know more about them and to, study them individually, they have to be separated from mixed forms and need to be cultured, under artificial conditions.This unit deals with Isolation of microorganisms and their growth, in the laboratoryconditions and also various culture techniques and instruments used, formicrobiological studies. After reading this unit,one will be ableto:, , , , , , , , 2.2, , Get an idea of the cultivation of microorganisms., Know about different culture media and their preparation., Understand the methods of isolationof microorganisms., Obtain pure cultures., Know about thecultivation and culture techniques ofviruses., Study the different microbiological instruments., , INTRODUCTION, , You know that microorganisms occur innatural environment; they arecontaminated, and mixed with several other forms of life. In order to understandmore about them we have to, separate and study them individually for this purpose we have to isolate microorganisms and, culture them under artificial conditions. The technique of growing microorganisms in an, artificial medium is known ascultivation., Cultivation of microorganisms is done in the laboratory and requires favorable, environmental conditions such as nutrient sources of energy, appropriate temperature, oxygen, and pH etc. Since various types of microorganisms grow together in a suitable environment, a, number of isolation techniques are used to obtain pure culture of just one species of a, microorganism., , 2.3, , STERILIZATION, , In microbiology Sterilization is an important term which needs making anything free, of any form of life. For detail study of a microorganism, one needs a pure culture of an, organism. It ia obtained by taking utmost care to avoid contamination through the, atmosphere, glassware, media or other instruments used in the culture technique. The growth, of unwanted microbes in the culture is called contamination and these unwanted microbes are, called contaminants., A number of precautionary measures are taken to prevent contamination during, sterilization and creating a germ free condition is called aseptic condition. There are, following three methods of sterilization:, (A) Physical, (B) Chemical, UTTARAKHAND OPEN UNIVERSITY, , Page 42
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (C) Gaseous, (A), Physical Methods :, The frequently used physical methods are, I., Sterilization by heat(a) Dry heat sterilization, (b) Wet heat sterilization, II., III., IV., , Sterilization by filtration, Sterilization by ultra violet radiations, Sterilization by ionizing radiations., I. Sterilization by heat-Heat is most commonly applied in the microbiological, laboratories for sterilization., (a) Dry heat sterilization: Direct heating of the instruments in a flame is an easy way of, sterilization. Inoculating needles, scissors, forceps, scalpels etc. are commonly, sterilized by direct heat while the neck and mouth of specimen tubes, flasks and, culture tubes are also passed through flame till they become sterilized. The process of, sterilizing the articles with flame is called flaming., Another method of dry heat sterilization is to keep thoroughly washed and dried glass, wares such as Petri dishes, beakers, flasks, culture tubes etc. inside thermostatically, controlled electric oven. Complete sterilization is accomplished by maintaining a, temperature of 1600C for not less than 4 hrs. inside the oven., , (b) Wet heat sterilization: Wet heat(steam) is more efficient method and is preferred in, sterilizing the media used for culturing micro-organisms. The common ways by which, Wet heat is employed in the laboratory are: Boiling, Pasteurization, Tyndallization, and autoclaving., i. Boiling: It is a common method of sterilization. All the instruments used for, cultivation are kept in a container filled with distilled water and allowed to boil for at, least 15 minutes. If the articles are not to be used immediately, these should be stored, in a sterile container., ii. Pasteurization: Many substances such as milk are treated with uncontrolled heating, at temperatures well below boiling. This process is called pasteurization. Milk, beer, and many other beverages are usually pasteurized. This process does not sterilize a, beverage, but it does kill any pathogen present. Milk can be pasteurized in two ways, (i) in the older method; the milk is heated at 630C for 30 minute. (ii) Flash, pasteurization consists of quick heating to about 720C for 15 seconds followed by, rapid cooling., iii. Tyndallization: Sometimes a heat sensitive material is sterilized by fractional steam, sterilization, called tyndallization. The container with the material to be sterilized is, heated at 90-1000C for 30minutes on each of three consecutive days and incubated at, 370C in between. The first heating will destroy all microbes except bacterial, endospores. Most of these germinate when incubated at 370C and are killed by the, UTTARAKHAND OPEN UNIVERSITY, , Page 43
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , second heating. Any remaining spores are destroyed by the second incubation and, third heat treatments, many materials specially the liquid media for microbial cultures., Autoclaving: Steam under pressure is more efficient method of sterilization this, technique and is known as autoclaving. Autoclave is a cylindrical metallic vessel with, double walls. There are various types of autoclaves in use., , iv., , 1) Simple autoclave: In which the body is made up of gun metal and it is cylindrical in, appearance and closed at one end by hinged door. A gasket seal is provided between, the door and cylinder. It can withstand high temperature. A perforated metal tray is, provided within the barrel which is used for keeping those articles which are to be, sterilized. The water present below the perforated tray is boiled by an electric heater, to produce the steam., 2) Steam jacketed autoclave: It is a modified form of simple autoclave. In simple, autoclave much of heat is wasted from the surface of barrel. To check this, a steam, jacket is provided around the barrel in large autoclave. Inside the autoclave steam, pressure is increased and the temperature increases proportionately. Usually, autoclaving is done at 15 lb. pressure for 15 minutes. The autoclave is used to sterilize, most of the solid and liquid media required for microbial cultures., , II., , Sterilization by filtration :, It is a best way to sterilize the solutions of heat sensitive materials. This method simply, removes the microbes instead of directly destroying them. There are two types of filters., (a) Depth filters: These consist of fibrous or granular materials that have been bonded, into a thick layer filled with twisting channels of small diameter. The solution, containing microorganisms is sucked through this layer under vacuum and microbial, cells are removed by physical screening, Depth filters are made of diatomaceous, earth, unglazed porcelain (chamberlain filters), asbestos filters etc., (b) Membrane filters: These filters have replaced depth filters. Such filters are circular, porous membranes, made of cellulose acetate, cellulose nitrate, polycarbonate,, polyvinylidene fluoride or other synthetic materials. Membranes with pores about 0.2,, 𝜇m in diameter are used to remove vegetative cells from solutions. The solution is, forced through the filler with a vacuum or with pressure from a syringe or nitrogen, gasbottle and collected in previously sterilized containers. Membrane filters remove, microorganisms like a sieve with minute pores., (c) Air sterilization by filtration: Air can also sterilize by filtration. Surgical masks and, cotton plugs on culture vessels are two common examples that let air in but keep, microorganisms out. Laminar flaw biological safety cabinets fitted with high, efficiency particulate air (HEPA) filters remove 99.97% particles from the air., , III., , Radiation:, Sunlight is the major source of radiation on the earth. It includes visible light, ultraviolet, radiation (UV), Infrared rays and radio waves. At the surface of the earth, very little UV, UTTARAKHAND OPEN UNIVERSITY, , Page 44
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , radiation is found. The ozone layer presents between 25 and 30 miles above the earth‘s, surface absorbs somewhat larger UV rays. This elimination of UV is crucial because it is, quite damaging to living system. UV rays kill all kinds of microorganisms due to its, shortwave length and high energy does not penetrate glass, dirt films, water and other, substances very effectively., Many forms of electromagnetic radiation are very harmful to microorganisms. As the, wavelength of electromagnetic radiation decreases, the energy of radiations increases e.g., gamma rays and x-rays are much more energetic than the visible light of infrared rays., Electromagnetic radiation acts like a stream of energy packets called photons. Each photon, possesses a quantum of energy whose value depends upon the wavelength of the radiation., , IV., , The ionizing radiations, because of very short wavelength or high energy cause atoms, to lose electrons ionize. Two major ionizing radiations are:, (i), X-rays produced artificially, (ii), Gamma rays– Which are emitted during ionizing radioisotope decay. Low levels, of ionizing radiations cause mutations and may indirectly results in death while, higher levels are directly lethal. Ionizing radiation is an excellent sterilizing agent, and penetrates deep into objects. Gamma radiation has also been used to, pasteurize meat and other food., (B), , Chemical Methods:, , It is a quick method of sterilizing instruments, glass apparatus or any other article, used in culture technique. The chemicals usually act as disinfectants because they cannot, readily destroy bacterial endopores. There are a number of chemicals known for their, property as:, (a) Disinfectant or germicidal (germ killing), e.g. Lysol, Cresol, etc., (b) Antiseptic (microbial growth stopping), e.g. Ethyl andisopropyl alcohols., (c) Sanitizer (reducing microbial population to sap limit), e.g. Silver nitrate, mercuric chloride and some other forms of mercury., (C), Gaseous Methods:, Many heat sensitive materials such as disposable plastic syringes, petridishes, catheters, heart, lung machine components etc. are now a days sterilized with ethylene oxide gas. It is both, microbicidal and sporicidal. It kills by combining with cell proteins. It is very effective, sterilizing agent as it rapidly penetrates packing materials, even plastic wraps., Betapropiolactone (BPL) is occasionally used to sterilize vaccines and sera. It also, destroys microorganisms more rapidly than ethylene oxide but does not penetrate materials, well and may be carcinogenic. Because of this, BPL has not been used extensively., , UTTARAKHAND OPEN UNIVERSITY, , Page 45
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 2.4, , BSCBO-101, , PREPARATION OF CULTURE MEDIA, , The organisms are grown on suitable culture media. A culture medium is a nutrient, preparation which provides a balanced mixture of the required nutrients at concentrations that, will permit good growth of microorganisms., The culture media are generally of following types:, I. Living culture media., II. Natural culture medium, III. Synthetic culture medium., IV. Complex media or non-Synthetic., , Culture media are variously classified as:, (A), , On the basis of composition :, , 1- Living culture media :, Such media require living cells, tissues or callus to be parasitized by the microorganisms, to be cultured. Chick embryo is commonly used for cultivation of certain viruses., 2- Natural or Empirical culture Media :, The empirical or natural media mostly contain either one or many in gradient. In such, medium, the exact composition is not defined. Natural media are convenient and, inexpensive. However, these are not ideal media for many organisms. Milk, Skim, milk, wine diluted blood, vegetable juices are some of the natural media., 3- Synthetic medium:, Synthetic medium is prepared by mixing many components in a particular ratio. In this, the exact chemical composition of the medium is known. Such media contain highly, pure organic and inorganic compounds. Nutrient Agar is synthetic medium., 4. Complex Media:, Complex media are those, in which chemical composition is not well defined. These, media are non- synthetic. These media are useful for culturing a variety of, microorganisms. Peptone, yeast extract, meat extract, Beef extract etc. used in, complex media., (B), On the basis of Physical state :, 1- Liquid media: These are defined as water based solutions that do not solidity at, temperature above freezing and flow freely when the Container is tilted. These media, are made by dissolving various solutes in distilled water. The liquid media are termed, broths, milks or infusions., 2- Semisolid Media: The media which exhibit a clot-like consistency at room, temperature are called semi soiled media. They do not flow freely. They contain a, solidifying agent agar or gelatin that thickens them but does not produce a firm, substrate. These are used to determine the motility of bacteria and to localize a, reaction at a specific site., 3- Solid Media: The media which provides firm surface on which cells can form, discrete colonies are called solid media. These are useful in isolating and sub, culturing bacteria and fungi. They are of two types., UTTARAKHAND OPEN UNIVERSITY, , Page 46
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (i) Liquefiable solid media: These are also called reversible solid media, They contain a, solidifying thermoplastic agent. The most widely used agent is agar-agar. Agar is, solid at room temperature and is flexible and mouldable. It has the property to hold, moisture and nutrients. It is a non-digestible nutrient for the vas- majority of, microorganisms., (ii) Non-liquefiable solid media: These are not thermoplastic. They includes materials, such as rice grains (used to grow fungi), cooked meat and potato slices. These media, start out solid and remain solid after heat sterilization., Potato dextrose agar (PDA), This is used for growing fungi and is prepared in the laboratory. The ingredients are :, Potatoes peeled and sliced – 200gm., Dextrose, – 20 gm., Agar, – 15 gm., Distilled water– 1000 ml., Potatoes sliced are first steam cooked in 500 ml water and agar is mixed in other 500, ml. water. Now both are mixed together; filtered and dextrose is added., (C) On the basis of function (Functional Types), 1. General Purpose media: Those media which support the growth of many, microorganisms, are called general purpose media., These are non- synthetic and contain a number of nutrients that could support the growth, of both pathogens and non-pathogens., 2. Enriched Media: The specially fortified media are called enriched media. These, contain complex organic substances such as blood, serum, hemoglobin or special, growth factors like vitamins, amino acids which are the requirments of some, microorganisms to grow. Bacteria that require growth factors and complex nutrients, are called as fastidious (e.g.: Streptococcus pneumonia)., 3. Selective and Differential Media: These media are meant for special microbial, groups. These help in the preliminary identification of a genus or even a species, in a, single step., (a) Selective Media: These contain one or more substances that inhibits the growth of, certain microbe/ microbes but not others e.g. Use of dyes like basic fuchsin and, crystal violet favours the growth of gram negative bacteria. Some selective media, contain strong inhibitory substances., e.g.: Tellurie is used to isolate oral streptococci from saliva., Some nutrients are used in the media specifically, e.g. cellulose for cellulose digesting, bacteria., (b) Differential Media: These media are used for the growth of several types of, microorganisms but are used to differentiate different groups of microbes. These are, also used for in tentative identification of microorganisms on the basis of their, biological variations. Variations maybe in colony size and the colour, the colour, changes of media and the formation of bubbles and precipitation properties. These, UTTARAKHAND OPEN UNIVERSITY, , Page 47
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , variations are due to the type of agents added and the way the cells react to them., Blood agar is a differential as well as enriched medium. It distinguishes between, hemolytic and non- hemolytic bacteria. Hemolytic bacteria produce clear zones, around their colonies as a result of red blood cell destruction., (D), , Some Miscellaneous Media:, , 1-, , Reducing Medium: A reducing medium contains a substance cystine that, absorbs oxygen reducing its availability. These media are useful in growing anaerobic, bacteria and also in determining oxygen requirement., , 2-, , Carbohydrate fermentation Medium: These contain sugars that can be, fermented., , 3-, , Transport Media: These are used to maintain and preserve specimens for a, period of time prior to clinical examination. These are also used to sustain delicate, species that die rapidly if not kept under stable condition., , 4., , Assay Media: These are used to test the effectiveness of antimicrobial drugs and also, to assess the effect of antiseptics, cosmetics and preservatives on the growth of, microorganisms., , 5., , Enumeration Media: These are used by industrial and environmental, microbiologists to count the numbers of organisms in milk, water, food, soil and other, samples., , 2.5, , DISPENSING THE MEDIUM, , Dispensing is the process in which the medium is poured into the sterilized flasks,, culture tubes and Petri dishes. The unsterilized medium is usually poured into the flasks and, culture tube by semiautomatic syringe, funnel and automatic filter. The liquid medium, (Broth) is dispensed into culture tube or flasks which are plugged with nonabsorbent cotton, wool plugs. The pouring of sterilized medium is usually carried out in Petri dishes which are, already sterilized in a special sterilized inoculation chambers., , 2.6, , SOME IMPORTANT CULTURE MEDIUM, , Some important media which are generally used for culturing the variousmicroorganisms are given below., (A), , For Bacteria, I. Nutrientagar: Beef extract, Peptone, -5.0 gm., Agar, - 15.0 gm., Distilled Water - 1,000 ml., , - 3.0 gm., , Heat unit/ agar and peptone dissolve. Adjust PH to 6.6 to 7.0., II. Asparagin Mannitol agar, K2HPO4----------------------1.0 gm., KNO3-------------------------0.5 gm., UTTARAKHAND OPEN UNIVERSITY, , Page 48
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , MgSo4 7H2O----------------0.2 gm., Fe cl3 6H2O------------------in traces., Nacl---------------------------0.1 gm., Asparagine-------------------0.5 gm., Mannitol---------------------1.0 gm., Agar--------------------------15.0 gm., distilled water---------------1,000ml., After the agar and salts have been dissolved add the mannital and adjust the PH to 7.4., Mac Conkey‘s agar medium is a typical selective medium. It made up of the, following components –, Peptone, Lactose, Neutralredsolution, ( 1%), Nacl, Bile salt, Agar, Crystal violet, Distilled water, , -, , 20 gm., 5gm., 10 ml., , -, , 5gm., 1.5 gm., 13.5 gm., 0.001gm., 1.000 ml., , It is used for the culture and isolation of gram negative lactose fermenting bacteria., , , Blood Agar is the most commonly used differential medium. The blood agar medium, consists of the following components ;, Infusion from beef heart, , -, , 500gm., , Tryptose, , -, , 10gm., , Nacl, , -, , 5gm., , Agar, , -, , 15gm., , Distilled water, , -, , 1000ml., , If mixtures of bacteria are inoculated into this medium, the hemolytic and nonhemolytic bacteria can be identified., (B) For fungi:, I. Potato dextrose agar (PDA), Potato and sliced potato -------------200gm., Dextrose--------------------------------20 gm., Agar-------------------------------------15 gm., Distilled water -------------------------1,000ml., II. Czapek- Dox agar :, Sucrose --------------------------30.0 gm., UTTARAKHAND OPEN UNIVERSITY, , Page 49
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Sodium nitrate ------------------2.0 gm., Potassium chloride -------------0.5gm, Magnesiumsulphate--------- 0.5 gm., Ferrous sulphate ----------------0.01 gm., Dipotassium phosphate--------1.0 gm., Agar ------------------------------15gm., Distilled water --------------------1,000ml., III. Rose- Bengal agar (Cooke’s medium), Glucose -----------------------------10.00 gm, Peptone -------------------------------5.00 gm., Dipotassium phosphate ----------- 1.00 gm., Magneciumsulphate ---------------0.50gm., Streptomycin -----------------------30.00gm., Agar ---------------------------------15.00 gm., Rose- Bengal----------------------- 0.035 gm., Distilled water --------------------- 1,000ml., The antibiotic is sterilized separately and added aseptically to the sterilized medium. The, medium is specially recommended for isolation of fungi in the presence of large, numbers of bacteria,, IV. Smith and Dawson’s medium :, Glucose --------------------- 10.0 gm., NaNo2----------------------1.0 gm., KH2 Po4--------------------1.0 gm., Agar -------------------------15.0gm., Rose Bengal ----------------0.067 gm., Soil extract------------------ 1,000 ml., The soil extract is prepared by autoclaving500 gmof loam soil in 1200 ml. water for one, hour. The extract is then filtered through paper., (C), , For Actinomycetes:, Ken knight and Munaier‘s medium, Dextrose ---------------------1.00 gm., KH2 Po4--------------------0.10 gm., NaNo3 ----------------------0.10 gm., Kcl---------------------------0.10gm., MgSo4 7H2O--------------0.10 gm., Agar -------------------------15.0gm., Distilled water---------------1,000 ml., (D) For specialized fungus :, (i) For Yeasts, Malt extract agar, , UTTARAKHAND OPEN UNIVERSITY, , Page 50
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Malt extract----------------------30.0 gm., Peptone---------------------------5.0 gm., Agar------------------------------20.0 gm., Distilled water------------------1,000 ml., (ii) For Aspergillus niger :, Raulins Medium, Sugar ------------------- 70.0 gm, Tartaric Acid----------- 4.0 gm., Ammonium nitrate ------4.0 gm., Potassium carbonate ------- 0.6 gm., Ammonium phosphate-----0.6 gm., Magnesium carbonate-------o.4 gm., Ammonium sulphate--------- 0.25 gm., Zinc sulphate (crystal)-------- 0.07 gm., Ferrous sulphate(crystal)------0.07 gm., Potassium silicate -------------0.07 gm., Distilled water ---------------- upto1,000ml., , 2.7, , METHODS OF OBTAINING PURE CULTURE, , Pure Culture: A culture containing only one type of microorganism is called a pure culture., The microbes are found distributed everywhere in nature and hence they occur only as a, mixed form. When culture media are inoculated with substances such as soil, water or, excreta, many kind of organisms develop simultaneously, and it results the growth of a mixed, culture of microbes. For the study of a single microorganism a pure culture of that organism, is required., Any technical procedure for obtaining pure culture is dependent upon the isolation of, a single viable microbe which is allowed to multiply in a suitable culture medium. The first, reliable method of isolation of pure culture was devised by Robert Koch in 1881 and his, theory is known as ‗Koch‘s Postulated‘, Koch’s Postulates, 1- The pathogen or organism must be constantly associated with the symptoms of the, disease in all diseased plants examined., 2- The pathogen must be isolated and grown in pure culture on nutrient media., 3- The pathogen from pure culture must be isolated and inoculated on healthy plants of, some species on which the disease appears. andit must produce the same symptom of, disease on inoculated plants., 4- The pathogenmust be again isolated in pure culture and its culture and characteristics, must be resemble with previous culture. So that the isolated pathogen is identified and, confirmed for the disease., , UTTARAKHAND OPEN UNIVERSITY, , Page 51
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , If nutrient agar isinoculated with fluid and is then solidified and kept underfavorable, temperature, many of the microbes that have been introduced are able to multiply and, formdistinct colonies. If the colonies are not closely crowded, a pure culture may be obtained, by touching a colony with the tip of a sterile needle and inoculating it in a fresh culture, medium., , 2.8, , METHODS OF ISOLATION, , The isolation of one kind of microorganisms from a mixture is called pure culture, technique. The petridishes or flasks with sterilized needles are inoculated with an organism, and are placed in culture chamber for its growth. Before inoculation both the hand and, inoculation instruments etc. are sterilized by wiping them with cotton wool soaked in alcohol., Some important methods used for obtaining pure culture are as follows:, I., Pour Plate Method :, In this method the mixed culture is diluted in sterile medium and the diluted mixture is added, to culture tubes containing melted agar medium. The contents of the tubes are then poured, into a sterile petridish and allowed to solidify. The plates are then incubated. The cells of, different of microorganisms develop into colonies and cells from individual colony are, picked up for further culture., II., Streak Plate method :, Streaking is the most widely used method of isolation. This method is most suitable for, bacterial and fungal cultures. In streak plate method, the mixed culture is taken on a sterile, wire loop (inoculum) and is drawn back and forth on a solid agar medium in a petridish. The, successive streaks thin out the culture sufficiently. In this method, isolated individual cells, are deposited on some region of the plate. The needle is flamed and allowed to cool after each, streaking. Several such streaks are made on the medium. The streaking is done in some, definite pattern (Fig.2.1)., , Fig.2.1 Different ways of streaking on agar plate, , Streaking method needs a lot of care not to break the surface of the medium during, streaking incubation each cell grows into a colony., , UTTARAKHAND OPEN UNIVERSITY, , Page 52
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , III., Serial Dilution Method :, The dilution of sample in successive stages is called serial dilution. This method is most, suitable for the bacteria and fungi which cannot be easily isolated by streaking method. The, mixture of microorganisms is diluted serially in culture tubes of sterile medium until the last, tube contains only a single organism. In this method, the dilution factor increases in a regular, fashion e.g.: 1/10, 1/100, 1/1000 etc., In this method 1ml. of sample is mixed to 9ml. of sterile water in culture tube. This gives a, tenfold dilution and this dilution factor is represented as 1/10 or 10-1, Now from this 10 fold, dilution, 1 ml. of sample is taken and is added to 9 ml. of sterile water taken in a second, culture tubes Now the second tube contains a 100 fold dilution and the dilution factor is, represented as 1/100 or 10-2, , Fig.2.2 Serial dilution technique, , Similarly from tube two, 1ml. of sample is taken and is added to 9 ml. of sterile, water taken in a third culture tube. Now the third tube contain a 1000 fold dilution factor, is represented as 1/1000 or 10-3. In same way, culture tubes 4 and 5 are prepared. Tube 5, provides 10-4 dilution and tube 5 provides 10-5 dilution. A 6thTube is prepared as a control, containing 10 ml. of sterile water only., Then from each tube, 1 ml. of diluted sample is taken and is added to an agar plate, (a petridish containing 10 to 15 ml. of melted agar medium). The 6 agar plates are, incubated at 25-300C for 24 hours. A luxuriant growth of most of the bacteria is obtained., By the serial dilution, the chance of dominant organism in pure condition in the culture is, increased. Ultimately, a little amount of the suspension is pipette out and spread over the, medium of petridish(Fig.2.2)., IV-, , Spread Plate Method:, , UTTARAKHAND OPEN UNIVERSITY, , Page 53
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , It is a modification pour plate method. In this method, the mixed culture is serially, diluted in sterile distilled water. A small amount of diluted mixture is then poured on the, surface of the agar plate and it is spread evenly using a sterile bent glass rod. The isolated, cells grow into colonies., V-, , Single cell method:, In this method, a suspension of microbes is placed on the cavity slide. Thereafter, a, single cell is removed with the help of sterile micropipette with the aid of a microscope. The, cell is then transferred to sterile culture. The colony obtained, originated from single cell., VI-, , Enrichment Culture Method:, In this method, a particular nutrient, which favours the growth of the desired, bacterium, is added to the medium. When the mixed culture is placed in this enriched, medium, the desired bacterium will grow dominantly., VII-, , Selective culture method:, In this method a selective medium is taken which contains a chemical, which, suppresses undesirable species. e.g.: Crysisal violet inhibits gram positive bacteria, when, crystal violet is added to the medium, the medium will select the gram negative bacteria., VIII- Differential Culture Method:, In this method the specific chemicals are used in the medium and different, microorganisms are isolated on the basis of their colour, e.g.: in eosin- methylene blue agar, medium, E. coli will produce colonies with a brilliant green metallic colour and Acrobactor, acrogens will produce pink colonies with dark centres., After obtaining the pure culture of a desired microbe, it may be grown and maintained, as a pure culture. This pure culture can be maintained by transferring the organisms from one, to another culture tube. This process is called subculturing., , 2.9 CULTIVATION OF VIRUSES, Viruses are unable to reproduce independently, So, they cannot be cultured like other, microorganisms. These are cultured indifferent ways depending upon the type of living host, which they require for multiplication., I. Cultivation of plant viruses:, Plant viruses can be cultivated in various ways. Plant tissue cultures, cultures of separated, cells or cultures of protoplast may be used for cultivating plant viruses, Viruses can also, be grown in whole plants. Leaves of a healthy plant are mechanically inoculated when, rubbed with a mixture of viruses and an abrasive such as carborudum orcelite. When the, cell walls are broken by the abrasive, the viruses come in direct contact with plasma, membrane and infect the exposed host cells. Alocalized necrotic lesion often develops, UTTARAKHAND OPEN UNIVERSITY, , Page 54
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , due to the rapid death of cells in the infected area. Even when lesions do not appear, the, infected plant may show other symptoms such as change in colour or leaf shape. Some, plant Viruses are transmitted only if a diseased part is grafted into a healthy plant., II. Cultivation of Animal Viruses :, In the past animal viruses were cultivated by inoculating suitable host animals or, embryonated eggs, usually six to eight days after laying. Before inoculation the shell, surface of egg is disinfected with iodine and penetrated with a small sterile drill. After, inoculation, the hole is sealed with gelatin and the egg incubated. Because viruses, reproduce only in a certain parts of the embryos, so they must be injected into the proper, region. The virus infection produces a local tissue lesion called pock appearance which, varies and is characteristic of the virus., Now a days, animal viruses are grown in tissue culture on monolayer of animal cells., This technique evolved with the development of growth media for animal cells and by the, discovery of antibiotics for the preventions of bacterial and fungal contamination., III. Cultivation of Bacteriophages :, Bacteriophages are cultivated in either broth or agar cultures of young, actively growing, bacterial cells. The number of host cells destroyed is so large that turbid bacterial cultures, may clear rapidly as a result of cellysis. For preparing agar culture the bacteriophage, sample is mixed with cool, liquid agar and a suitable bacterial culture. This mixture is, then quickly poured into a petridish containing a bottom layer of sterile layer. Wherever a, virion comes to rest in the top agar, the virus infects an adjacent cell and reproduces, eventually. Bacteriallysis result in a plaque in the opaque layer. The appearance of plaque, is characteristic of the phage being cultivated., , 2.10 CULTURE TECHNIQUES, Microbiologists use five basic techniques (also called five I‘s) to culture, manipulate,, examine and characterize microorganisms. These are:, (i), Inoculation, (ii), Isolation, (iii) Incubation, (iv), Inspection, (v), Identification, These techniques are used by all microbiologists, whether a beginner laboratory, student or researcher is attempting to isolate a useful bacterium from the soil or a clinical, microbiologist trying to find out the cause of patient‘s infection. These techniques thus, help, in handling and maintaining microorganisms as discrete entities., (i) Inoculation: The process of transfer of inoculum (a sample containing, microorganisms) into a container of nutrient medium, which provides an environment, in which they grow is called inoculation. Inoculum may be obtained from soil, water, sewage, foods, air and inanimate objects. For determining the cause of an infectious, UTTARAKHAND OPEN UNIVERSITY, , Page 55
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , disease, inoculum is obtained from body fluid (blood, cerebrospinal fluid), discharges, (Sputum, urine, faeces) or diseased tissue., The culture vessels (culture tubes, conical flasks, or petridishes) containing appropriate, culture media are inoculated using tools such as loops, needles, pipettes, etc. For a, properly controlled experiment, sterilization of the glassware, equipment and culture, media is necessary. This means that the inoculation must start with a sterile medium. All, inoculating tools and culture vessels should be sterile. Measures are also taken to prevent, the entry of undesirable microbes while inoculating. This procedure is carried out in, special rooms fitted with UV lamps. Now a days for inoculation, special laminar flow, (biological safety cabinets), fitted with HEPA fitters are used., For inoculation in culture tubes agar slants are prepared., Preparation of Agarslants:, Liquified agar medium is poured into culture tubes. The culture tubes are plugged, with cotton wool and sterilized in autoclave. The sterilized tubes are taken out and placed in a, slanting position and then allowed to cool. The sloppy surface provides maximum area of the, agar medium in the culture tube for the growth of microorganisms (Fig.2.3)., , Fig.2.3 Culture tube with agar slant, , Transfer of the Inoculum: The inoculation is done in inoculation chamber, completely, sterilized with ultraviolet light. The hand should also be cleaned and sterilized with rectified, spirit. For culture tube inoculation, the tube containing inoculum with sterilized agar medium, slant is held in one hand and the inoculating needle in the other. The cotton plugs of the tubes, are taken out with the help of fingers in front of the flame of spirit lamp. The inoculum is, picked out with the help of needle and then inserted within the agar surface of the tube., Plugging of the tube is immediately done to avoid contamination. For petridish inoculation,, the lid is removed to a minimum and inoculation is done in the centre of the dish. The, inoculated tubes or petridishes are finally incubated at desired temperature., (ii) Isolation: Isolation is separation of the pathogen from host tissue or from mixed, culture or its inoculation in culture media. To achieve proper isolation, a small, number of cells is inoculated into a relatively large volume or an expansive area of, medium. It generally requires (i) a medium with firm surface (ii) a petri plate (a clear, flat dish with a cover) and (iii) an inoculating loop. There are several ways of, isolation to obtain pure culture: as I. Pour plate method II. Streak plate method III., Serial Dilution method. IV. Spread plate method V. Single cell method. VI., Enrichment culture method VII. Selective Culture method. VIII. Differential culture, method., All these methods of isolation are already discussed in detail in earlier chapter., UTTARAKHAND OPEN UNIVERSITY, , Page 56
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (iii)Incubation: Once a culture vessel containing medium is inoculated, it is placed in a, temperature controlled chamber or incubator to facilitate multiplication. This is called, incubation. Usually they are incubated at 20 to 400C in Laboratory. Incubators can, also control the content of atmospheric gases like oxygen and carbon dioxide that may, be required for the growth of microbes. During the incubation period, the microbe, multiplies and produces some visible manifestation of growth., (iv) Inspection: It is essential to inspect a culture macroscopically during various stages, of inoculations. Colonies of microorganisms are readily visible especially the colonies, of bacteria and fungi appears. Colonies are actually large masses of clinging cells., The colonies exhibit distinctions in size, shape, colour and texture. Colony, development on agar surface helps the microbiologists in identifying microorganisms., Once a microorganism is isolated, it is a standard practice to make a second level., Cultural called a subculture. This is done by removing a small sample from one well, isolated colony and transferring it into a separate container of media. Because a, colony consists of only one type of microorganism, it yields a pure colour or auxenic, culture for further testing and identification., Cultural inspection is also done by using a microscope. This gives information of, many characteristics of cell microbiology including size, shape and details of internal, and external structures., (v) Identification: The microorganisms isolated are identified by a combination of, microscopic and macroscopic appearance. These are useful in differentiating simple, prokaryotic cells from larger complex eucaryotic cells. Although, appearance is of no, use in the identification of bacteria because of similar morphologies. For their, identification other techniques that characterize their cellular metabolism are used., These involve biochemical tests that can determine fundamental chemical, characteristics such as nutrient requirements, products releasing during growth,, temperature and gas requirements and methods of deriving energy., By compiling macroscopic and microscopic characters and results of biochemical, tests, a profile is prepared which is then used in the final identification of a microbe., Thus, microorganisms are identified in terms of their macroscopic morphology, their, microscopic characters, and their biochemical reactions and genetic characteristics., Maintenance of culture:, Culture of microorganism is maintained for further studies. Many research, laboratories require a line of stock cultures. The stock cultures are continuously maintained, species that represent ―living Catalogues‖. The largest culture collection is ‗American Type, culture collection located in Rockville, Maryland, U.S.A. It maintains frozen and freeze-dried, fungal, bacterial, viral and algal cultures., Disposal of cultures:, Some cultures are potential health hazard. Therefore, they require immediate and, proper disposal. Microbial cultures are disposed off in two ways: (1) Steam sterilization by, UTTARAKHAND OPEN UNIVERSITY, , Page 57
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , autoclave, and (ii) incineration (burning). Both are effective methods for destroying, microorganisms., , 2.11 INSTRUMENTS USED IN MICROBIOLOGICAL STUDIES, Following are some of the basic requirements and equipments for culturing, microorganism under artificial conditions:, I. Culture vessels: Culture media are contained in culture vessels usually culture tubes,, conical flasks and petridishes. These are made of high quality corning glass. The petri, dishes are special culture dishes named after their inventor Julies Richard Petri. Petri, developed these dishes in 1887. They consists of two round halves, top half, overlapping the bottom., , Fig.2.4 Culture vessels; A. Culture tube B. Conical flask. C. Petri disc. D. Culture Bottles, , Culture tubes are of two size, the smaller are without rim and Large with rim. Almost all, sizes of flasks ranging from 50 ml to 1000 ml are used for microbial culture. These, are used to contain culture media before and after the sterilization and also for culture, the pathogen in liquid or semisolid medium (Fig.2.4)., II. Plugs: Tubes and flasks containing media or culture are always plugged with cotton, wool so that, any air which enters inside is filtered from all contaminating, microorganisms. A plug should project inside the tube about an inch and should have, tuft outside the tube, by which it can be taken out. The plug should fit accurately and, tightly, but not so tightly that it cannot be extracted when gripped between any two, fingersof one hand. The plug should also retain its shape, so that after withdrawl, it, can readily be a reinstered., III. Inoculating tools: For inoculation, tools like inoculating needles, inoculating loops,, syringes, etc. are used. Inoculating needles/ loops are made up of plantinum wire/, nichrome wire fixed into a metal or glass rod at one end. In inoculating needles the, wire is straight whereas in inoculating loops, the free end of the wire is bent in the, form of a loop (Fig.2.5)., , UTTARAKHAND OPEN UNIVERSITY, , Page 58
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.2. 5 Inoculating tools: A. Inoculation needle, B. Inoculation loop, C. Syringe, , IV Sterilization Equipments:, Following equipments are used in sterilization of glass ware and culture media:, (i), Oven for dry sterilization, (ii), Autoclave for steam sterilization, (iii) Filter sterilization Equipment, (iv), Sterile rooms or inoculation chambers, (v), Laminar flow biological softy cabinets, (i) Oven for dry sterilization:, Dry heat is mainly used to sterilize glass ware or other heat stable materials. The, objects are wrapped in aluminium foil and exposed to a temperature of 1700C for 90, minutes in an oven. It is an electrically operated device. It consists of a big chamber, with insulated walls and is fitted with electrical hearers to raise the temperature level, and a thermostat to maintain temperature at a desired level (Fig.2.6)., , Fig.2.6. Hot air oven, , (ii) Autoclave: Autoclave is the instrument used to sterilize culture media, glass ware and, other tools by high pressure steam, which developed inside the sterilizing chamber by, heating water. Steam pressure increases inside the chamber with increasing heating, time. The body of autoclave is made up of a thick double walled cylinder. Inside the, UTTARAKHAND OPEN UNIVERSITY, , Page 59
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , cylinder at its bottom is fitted an electric immersion rood. The mouth of the cylinder, is fitted with a heavy tightly fitting lid. A pressure gauge is attached to the lid to, monitor pressure inside the cylinder. An outlet valve is also attached to the lid., Laboratory autoclaves are commonly operated at a steam pressure of 15lbm 2 above, atmospheric pressure which corresponds to a temperature of 1200C. Even bacterial, spores that survive several hours of boiling are rapidly killed at 1200C. The, temperature at 15lb pressure for 15minutesis sufficient to kill any organism, and to, achieve complete sterility. If an autoclave is not available, pressure cookers can be, used for purpose of sterilization (Fig.2.7)., , Fig.2.7 Autoclave, , (iii)Filter Sterilization Equipment :, Solutions of heat labile materials are sterilized by filtration through filters capable of, retaining microorganisms. The most commonly used filters are:, 1. Membrane filters (Millipore filters): These consist of porous discs of, cellulose esters., , 2. Seitz filters: these consist of discs of asbestos cellulose mixture., , UTTARAKHAND OPEN UNIVERSITY, , Page 60
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 3. Sintered glass filters: These are prepared by fusing together fine glass, fragments., , 4. Candle filters: These are made up of unglazed ceramic., , Fig.2.8 A to D Various types of filters, , The filter is appropriately mounted on a funnel like structure. The mounting is inserted into a, receiving flask. The complete assembly is sterilized by heat. The solution to be sterilized is, poured into the filter. Its passage through filter is accelerated either by suction on the, receiving flask or by pressure on the unfiltered liquid (Fig.2.8. A-D)., (iv) Sterile Rooms (Inoculation chambers) :, Inoculation is done in sterile rooms or inoculation chambers. These are fitted with, ultraviolet bulbs / lamps which emit UV light in wave length range 260 to 270 mm., They are useful for killing microbes in air and on object surfaces., UTTARAKHAND OPEN UNIVERSITY, , Page 61
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (v) Laminar flaw Biological Safety Cabinets :, The laminar flaw cabinets are available in different sizes. They can be placed where, needed and thus, eliminated the necessity for a separate room. Laminar flow, biological safety cabinets are filled with high efficiency particulate air (HEPA) fitters, which remove 99.97% of 0.3 𝜇𝑚particles. These are one of the most important air, filtration systems. Laminar flaw cabinets force air through HEPA fitters, then project, a vertical curtain of sterile air across the cabinet opening to protect a researcher from, microorganisms being handled within the cabinet and to prevent room contamination, (Fig.2.9)., , Fig.2.9, A schematic diagram showing the air flow pattern in a biological safety cabinet, , V., Incubators: Majority of fungi grow reasonably well at room temperature, however in, order to induce maximum rate of growth and in some cases, to promote the formation of, certain type of spores and fruiting structures, higher or lower temperature is essential., Incubator is the instrument, used for such purpose. It is an electrical instrument similar to hot, air ovens in construction and operation. The range of temperature varies from room, temperature generally between 200C to 50 or 600C. The cultures of microbes are incubated at, suitable temperature in these chambers (Fig.2.10)., , Fig.2.10, An incubator for maintaining cultures, , VI. Colony Counters:, This device is used to count the colonies of microorganisms developing on a culture plate., These are generally of 2types A., Quebec colony counter :, UTTARAKHAND OPEN UNIVERSITY, , Page 62
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , In quebec colony counter, there is a platform which is marked with cross ruling (small, squares). An illuminator is there below the platform to illuminate the colonies and above the, platform is present a magnifying lens. This lens magnifies the colonies and thus helps in, counting. For counting the colonies, the culture plate is mounted on the platform and, illuminated from below. The colonies are counted easily against back ground of small squares, (Fig 2.11. A)., B., Electrical colony counter :, The electrical colony counters are fined with an electrode for marking the location of each, colony, when a colony is touched by the electrode; it is automatically recorded in the counter, (Fig.2.11. B)., , Fig.2.11. Colony counters A. Quebec colony counter B. Electrical colony counter, , C., Counting Chambers :, To determine microbial members through direct counting, counting chambers are used. These, are easy, inexpensive and relatively quick. It also gives information about the size and, morphology of the organisms, being counted. Petroff Hausser counting chambers are used, for counting bacteria. Haemocytometers are used for counting large eukaryotic, microorganisms. Large microorganisms such as protozoa, algae and yeasts (non filamentous, forms) can be directly counted with electric counters like coulter counter. It gives accurate, results with larger cells and is extensively used to count red and white blood cells. It is not, useful in counting bacteria because of small debris particles, formation of filaments etc, (Fig.2.12)., , UTTARAKHAND OPEN UNIVERSITY, , Page 63
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.2.12 Coulter counter, , 2.12 SUMMARY, In this unit you have learnt that –, , , , , , , , , , , , , , , Microorganisms occur in natural environments; they are contaminated and mixed with, several other form of life., To study microorganism individually we have to separate them from mixed forms and, culture or grow them under artificial conditions., As they are widely distributed and undesirable microbes may enter into an experiment, and cause misleading results. To overcome these problem different methods like, sterilization, pure culture etc is done., In the isolation of microorganism for detailed study, one must take care to avoid, contaminations, for this various sterilization methods are used to produce aseptic, condition for microbial culture., The microorganisms are grown on suitable culture media. A culture medium is a, nutrient preparation which provides a balanced mixture of the required nutrients at, concentrations that will permit good growth of microorganism., Various types of culture media are prepared for different microorganisms, nutritional, requirements of microbes vary from a few simple inorganic compounds to complex, organic compounds. So culture media used for culturing microbes are extremely, varied in nutrient component and consistency., Microorganisms usually grow in complex, mixed, population containing several, types. Isolation of single species or single microorganism is done to obtain pure, culture or auxenic culture various ways like spread plate method streak method,, Dilution methods, pour plate method, etc. are used to get pure culture or single, individual., For culturing obligate parasites (that cannot grow on artificial media) e.g. viruses, live, cell culture or host animals are required., , UTTARAKHAND OPEN UNIVERSITY, , Page 64
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , BSCBO-101, , For all the culture process, to grow, to examine and to characterize microorganisms, five basic techniques are used by all microbiologists. These are: (1) Inoculation (ii), Incubation (iii) Isolation (iv) Inspection and (v) Identification., Culture vessels, inoculation tools, sterilization equipments, inoculation chambers,, Laminate flow, incubators, colony counters and counting chambers are the basic, equipments used in culture techniques., , 2.13 GLOSSARY, Acclimated micro-organism: Any microorganism that is able to adapt to environmental, changes, such as change in temperature., Actinomycetes: A group of micro-organisms apparently intermediate between bacteria and, fungi, and classified as either., Agar: A gelatin like material obtained from red algae and used to prepare culture media on, which microbes are grown., Antimicrobial: A chemical that either destroys or inhibits the growth of microscopic and, submicroscopic organisms., Auxenic culture: Pure culture i.e. a microorganism of a single species, growing in a medium, free of other microorganisms., Bacterial filter: A special type of filter through which bacterial cells cannot pass., Bacteriophage: A virus that infects specific bacteria and usually kills them., Bacteriostatic: A chemical or physical agent that prevents bacterial growth and their, multiplication without killing., Culture: to grow microorganisms artificially on a prepared food material., Culture medium: The prepared food material on which micro-organisms are cultured., Disinfectant: A physical or chemical agent that frees a plant, organ or tissue from infection., Incubation period: The Period between penetration of a host by a pathogen and its first, appearance of symptoms on the host., Inoculate: To bring a pathogen into contact with ahost plant., Inoculation: Transfer of a pathogen into a host or culture media., Inoculum: The pathogen or causal part which causes disease when brought into contact with, the host., Isolate: A single spore or culture derived from a mixture of microbes culture., Isolation: Separation of a pathogen or microbe from the host and its culture on a nutrient, medium., , UTTARAKHAND OPEN UNIVERSITY, , Page 65
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Mechanical Inoculation: Inoculation of plant with a virus through transfer of sap from a, virus infected plant to a healthy plant., Secondary Inoculum: Inoculum produced by Infections that took place during the same, growing season., Serum: The watery portion of the blood remaining after coagulation., Sterilization: The elimination of pathogen or microorganisms from any surface, or making, free from microbes., Virus: A submicroscopic obligate parasite consisting of nucleic acid and protein., , 2.14 SELF ASSESSMENT QUESTIONS, 2.14.1 Choose the correct answer from the given below:, (a) Agar agar is obtained from:, (i) Blue green algae, (iii) Brown algae, , (ii) Green algae, (iv) Red algae, , (b) Special culture dishes were invented by:, (i) Robert Kotch, (ii) Julius Richard Petri, (iii) Coulter, (iv) None of the above, (c) The instrument in which wet heat sterilization is done to sterilize objects is:, (i) Autoclave, (ii) Laminar flow, (iii) Hotair oven, (iv) Inoculation chamber, , 2.14.2 Fill in the blanks:, (a), (b), (c), , A medium of known composition is called....................... medium., A Pure culture is a population of cells derived from......................., One of the most important air filtration system filled with high efficiency particulate, air (HEPA) is..................................., , 2.14.3 Answer the following in one word or in one sentence:, (a), (b), (c), , How are heat labile materials sterilized?, Name the electrical counter with the help of which largemicroorganisms such as, protozoa, algae and yeasts can be directly counted., Heat sensitive materials e.g. disposable plastic, syringes, petri dishes, catheters etc., are sterilized with which chemical?, , 2.14.4 Write True or False (T/F):, (a) Cultivation of microorganism on a solid agar medium in a culture tube kept in a slanting, position is called agarslant culture., UTTARAKHAND OPEN UNIVERSITY, , Page 66
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (b) The process of transfer of a sample containing micro organism into a container of, nutrient medium is called incubation., (c) Selective and differential media are extensively used in isolation and identification of, microbes., 2.14.5 Explain the following –, (a), , Types of culture media., , (b), , Methods of sterilization for cultivation., , (c), , Instruments used in cultivation of microbes., , Answers Keys:, Q.1- (a)-(iv), (b)-(ii), (c)-(i), Q.2- (a)-Synthetic, (b)-single cell, (c)- Laminar flaw cabinets, Q.3- (a)-Filter sterilization, (b)-Coulter counter, (c)-Ethyline oxide, Q.4-(a)-True, (b)-False, (c)- True, , 2.15 REFERENCES, , , , , , , , , , , , , , , Ananthanarayan&Panicker, 1997, Text Book of Microbiology oriental Long man, publishers., Bhagat Singh and Renu Singh, 2011. Microbiology for Medical sciences. I.K., International Publishing House Pvt. Ltd., New Delhi., Baron, E.J., Peterson, L.R. &Finegold, S.M. Bailey &Scolt's Diagnostic, Microbiology, 1990, Mosby Publishers., Casida, L.E. 1968, Industrial Microbiology, John wiley and sons, New York., Doelle, H.W. and C.G. Heden 1986. Applied Microbiology, Kluwer Academic Press,, London., Kamat, M.N. 1953. Practical Pathology. Prakash Publishing, Poona., Kaushik. P. 1996, Introductory Microbiology. Emkay Publ. Delhi., Mukherjee , K.G. and Ved Pal Singh, 1997. Frontiers in Applied Microbiology,, Rastogi Publ. Meerut., Norris, J.R. and D.W. Ribbons 1970. Methods in Microbiology. Academic Press,, London., Power, C.B. and H.F. Daginawala 1996. General Microbiology 2 vols. Himalaya Pub., House, New Delhi., Prescott, I.J., J.P.M. Harley & A.D. Klein, Microbiology. Tata MC Graw Hill., Robinson, R.K. 1990, Dairy Microiology. Elsevier Applied Sciences, London., Ross, F.C. 1983. Introductory Microbiology. Charles E. Merril Publ. Co. Columbus., Ohio., , UTTARAKHAND OPEN UNIVERSITY, , Page 67
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 2.16. SUGGESTED READINGS, 1., , Alexander, M. 1971. Microbial Ecology, John willeg& sons., , 2., , Brock, T.D. & M.T. Madigen. Biology of Micro-organisms prentice Hall., , 3., , Bridge, E.A. Modern Microbiology. WMC Brown Publisher, oxford England., , 4., , Bhagat Singh and Renu Singh, 2011.Microbiology for medical sciences. I.K., International Publishing House Pvt. Ltd. New Delhi., , 5., , Dubey, R.C. & D.K. Maheshwari, A text Book of Microbiology. S. Chand & Co., Delhi., , 6., , Kaushik, P. 1996. Introductory Microbiology.EmkayPubl, Delhi., , 2.17. TERMINAL QUESTIONS, 1., , Give an account of the cultivation of micro organisms., , 2., , Write short notes on the following –, (i)Synthetic media, , (ii) Non synthetic media, , (iii)Autoclave, , (iv) Laminar Flow biological safety chamber, , (v) Koch‘s postulates, , (vi) Dry heat sterilization., , 3., , Describe briefly the Basic requirements and apparatus for culturing microorganism., , 4., , Discuss the different types of culture media used for successful culturing of microbes., , 5., , Define sterilization with reference to microbiology Discuss different sterilization, methods., , 6., , Describe in brief the five basic techniques of culturing microorganisms under, artificial conditions., , 7., , Differentiate the following –, i), Pure culture and Mixed culture, ii), Selective media and Differential media, iii), Inoculation and contamination, iv), Pasteurisation and Tyndallisation, , UTTARAKHAND OPEN UNIVERSITY, , Page 68
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-3- STRUCTURE, CLASSIFICATION,, NUTRITION, REPRODUCTION AND ECONOMIC, IMPORTANCE OF BACTERIA, 3.1-Objectives, 3.2-Introduction, 3-3-Structure of Bacteria, 3.4-Classification, 3.5-Nutrition, 3.6-Reproduction, 3.7-Economic Importance, 3.8- Summary, 3.9- Glossary, 3.10-Self assessment question, 3.11-References, 3.12-Suggested Readings, 3.13-Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 69
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 3.1 OBJECTIVES, After reading this unit student will be able:, , , , , , , To study the structure of bacteria., To understand the characteristic features of bacteria., To know different shapes of bacteria., To classify the bacteria., To analyze the nutrition and economic importance of bacteria., , 3.2-INTRODUCTION, ―Bacteria, the Hidden Heroes of the earth are very much powerful‖, Bacteria Bacteria are microscopic unicellular prokaryotic organisms characterized by the, lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part, of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera., Bacteria fall into one of the two groups, Archaebacteria (ancient forms thought to have, evolved separately from other bacteria) and Eubacteria. A recently proposed system classifies, the Archaebacteria, or Archaea, and the Eubacteria, or Bacteria, as major groupings, (sometimes called domains) above the kingdom level., Bacteria were the only form of life on earth which exist for 2 billion years. They were first, observed by Antony van Leeuwenhoek in the 17th century; bacteriology as an applied, science began to develop in the late 19th century, as a result of research in medicine and in, fermentation processes, especially by Louis Pasteur and Robert Koch., These microorganisms remarkably adaptable to diverse environmental conditions. They are, found in the bodies of all living organisms and on all parts of the earth—in land, terrains and, ocean depths, in arctic ice and glaciers, in hot springs, and even in the stratosphere. Our, understanding of bacteria and their metabolic processes has been expanded by the discovery, of species that can live only deep below the earth's surface and by species that thrive without, sunlight in the high temperature and pressure near hydrothermal vents on the ocean floor., There are more bacteria, as separate individuals, than any other type of organism; there can, be as many as 2.5 billion bacteria in one gram of fertile soil., , 3.3 STRUCTURE OF BACTERIA, Bacteria display a wide diversity of shapes and sizes. Their cells are about one-tenth the size, of eukaryotic cells and are typically 0.5–5.0 micrometers in length (Fig.3.1). However, a few, species- for example, Thiomargarita namibieniensis and Epulopiscium fishelsoni - are up to, half a millimetre long and are visible to the unaided eye; E. fishelsoni reaches, 0.7 mm. Among the smallest bacteria are members of the genus Mycoplasma, which measure, , UTTARAKHAND OPEN UNIVERSITY, , Page 70
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , only 0.3 micrometres, as small as the largest viruses. Some bacteria may be even smaller, but, these ultra microbacteria are not well-studied., , Fig.3.1: The Bacterial cell, , Most bacterial species are either spherical, called cocci (sing. coccus, from Greek kókkos,, grain, seed), or rod-shaped, called bacilli (sing. bacillus, from Latin baculus, stick)., Elongation is associated with swimming. Some bacteria, called vibrio, are shaped like, slightly curved rods or comma-shaped; others can be spiral-shaped, called spirilla, or tightly, coiled, called spirochaetes. A small number of species even have tetrahedral or cuboidal, shapes. More recently, bacteria were discovered deep under Earth's crust that grows as, branching filamentous types with a star-shaped cross-section. The large surface area to, volume ratio of this morphology may give these bacteria an advantage in nutrient-poor, environments. This wide variety of shapes is determined by the bacterial cell, wall and cytoskeleton, and is important because it can influence the ability of bacteria to, acquire nutrients, attach to surfaces, swim through liquids and escape predators., , UTTARAKHAND OPEN UNIVERSITY, , Page 71
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.3.2: A biofilm of thermophilic bacteria in the outflow of Mickey hot Springs, Oregon,, approximately 20 mm thick, , Many bacterial species exist simply as single cells, others associate in characteristic patterns:, Neisseria form diploids (pairs), Streptococcus form chains, and Staphylococcus group, together in "bunch of grapes" clusters. Bacteria can also be elongated to form filaments, for, example the Actinobacteria. Filamentous bacteria are often surrounded by a sheath that, contains many individual cells. Certain types, such as species of the genus Nocardia, even, form complex, branched filaments, similar in appearance to fungal mycelia., , Fig.3.3- The range of sizes shown by prokaryotes, relative to those of other organisms, and biomolecules, , Bacteria often attach to surfaces and form dense aggregations called biofilms or bacterial, mats (Fig.3.2). These films can range from a few micrometers in thickness to upto half a, meter in depth, and may contain multiple species of bacteria, protists and archae. Bacteria, living in biofilms display a complex arrangement of cells and extracellular components,, forming secondary structures such as microcolonies, through which there are networks of, UTTARAKHAND OPEN UNIVERSITY, , Page 72
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , channels to enable better diffusion of nutrients. In natural environments, such as soil or the, surfaces of plants, the majority of bacteria are bound to surfaces in biofilms. Biofilms are also, important in medicine, as these structures are often present during chronic bacterial infections, or in infections of implanted medical devices, and bacteria protected within biofilms are, much harder to kill than individual isolated bacteria (Fig.3.3)., Even more complex morphological changes are sometimes possible. For example, when, starved of amino acids, Myxobacteria detect surrounding cells in a process known as quorum, sensing, migrate toward each other, and aggregate to form fruiting bodies up to, 500 micrometres long and containing approximately 100,000 bacterial cells. In these fruiting, bodies, the bacteria perform separate tasks; this type of cooperation is a simple type, of multicellular organisation. For example, many cells migrate to the top of these fruiting, bodies and differentiate into a specialised dormant state called myxospores, which are more, resistant to drying and other adverse environmental conditions than are ordinary cells., , The bacterial surface, Cell Wall: The cell envelop is composed of the plasma membrane and cell wall. As in other, organisms, the bacterial cell wall provides structural integrity to the cell. In prokaryotes, the, primary function of the cell wall is to protect the cell from internal turgor pressure caused by, the much higher concentrations of proteins and other molecules inside the cell compared to, its external environment. The bacterial cell wall differs from that of all other organisms by, the presence of peptidoglycans which is located immediately outside of the cytoplasmic, membrane. Peptidoglycan is made up of a polysaccharide backbone consisting of alternating, N-Acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) residues in equal amounts., Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the, determination of cell shape. It is relatively porous and is not considered to be a permeability, barrier for small substrates. While all bacterial cell walls (with a few exceptions e.g., extracellular parasites such as Mycoplasma) contain peptidoglycan, not all cell walls have the, same structures. The cell wall is required for bacterial survival, but several antibiotics stop, bacterial infections by interfering with cell wall synthesis. There are two main types of, bacterial cell walls, those of gram-positive bacteria and those of gram-negative bacteria,, which are differentiated by their Gram-staining characteristics. For both these types of, bacteria, particles of approximately 2 nm can pass through the peptidoglycan. If the bacterial, cell wall is entirely removed, it is called a protoplast but when it is partially removed, it is, called a spheroplast. β-Lactam antibiotics such as penicillin inhibit the formation of, peptidoglycan cross-links in the bacterial cell wall. The enzyme lysozyme, found in human, tears, also digests the cell wall of bacteria and is the body's main defence against eye, infections in human beings., , The gram-positive cell wall, Gram-positive cell walls are thick and the peptidoglycan layer constitutes almost 95% of the, cell wall in some gram-positive bacteria and as little as 5-10% of the cell wall in gramnegative bacteria. The cell wall of some gram-positive bacteria can be completely dissolved, by lysozyme. In other gram-positive bacteria, such as Staphylococcus aureus, the walls are, UTTARAKHAND OPEN UNIVERSITY, , Page 73
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , resistant to the action of lysozyme. The matrix substances in the walls of gram-positive, bacteria may be polysaccharides or teichoic acids. The latter are very widespread, and found, only in gram-positive bacteria. There are two main types of teichoic acid: ribitol teichoic, acids and glycerol teichoic acids. The latter one is more commonly found. These acids are, polymers of ribitol phosphate and glycerol phosphate, respectively, and only located on the, surface of many gram-positive bacteria. However, the exact function of teichoic acid is not, fully understood. A major component of the gram-positive cell wall is lipoteichoic acid. One, of its purposes is providing an antigenic function. The lipid element is to be found in the, membrane where its adhesive properties assist in its anchoring to the membrane (Fig.3.4)., , Fig.3.4: Cell Wall composition of Bacteria, , The Gram-negative cell wall, Gram-negative cell walls are thin and unlike the gram-positive cell walls, they contain a thin, peptidoglycan layer adjacent to the cytoplasmic membrane. The chemical structure of the, outer membrane's lipopolysaccharides is often unique to specific bacterial sub-species and is, responsible for many of the antigenic properties of these strains. Lipopolysaccharides, also, called endotoxins, are composed of polysaccharides and lipid A which are responsible for, much of the toxicity of gram-negative bacteria. It consists of characteristic lipopolysaccarides, embedded in the membrane (Fig.3.4)., , Plasma Membrane: The plasma membrane or bacterial cytoplasmic membrane is, composed of a phospholipid bilayer and thus has all of the general functions of a cell, UTTARAKHAND OPEN UNIVERSITY, , Page 74
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , membrane such as acting as a permeability barrier for most molecules and serving as the, location for the transport of molecules into the cell. In addition to these functions,, prokaryotic membranes also function in energy conservation as the location about which a, proton motive force is generated. Unlike eukaryotes, bacterial membranes (with some, exceptions e.g. Mycoplasma and methanotrophs) generally do not contain sterols. However,, many microbes do contain structurally related compounds called hopanoids which likely, fulfil the same function. Unlike eukaryotes, bacteria can have a wide variety of fatty, acids within their membranes. Along with typical saturated and unsaturated fatty acids,, bacteria can contain fatty acids with additional methyl, hydroxy or even cyclic groups. The, relative proportions of these fatty acids can be modulated by the bacterium to maintain the, optimum fluidity of the membrane., , Fig.3.5. - Structure of bacterial plasma membrane, , As a phoshpholipid bilayer, the lipid portion of the outer membrane is impermeable to, charged molecules. However, channels called porins are present in the outer membrane that, allow for passive transport of many ions, sugars and amino acids across the outer membrane., These molecules are therefore present in the periplasm, the region between the cytoplasmic, and outer membranes. The periplasm contains the peptidoglycan layer and many proteins, responsible for substrate binding or hydrolysis and reception of extracellular signals. The, periplasm is thought to exist in a gel-like state rather than a liquid due to the high, concentration of proteins and peptidoglycan found within it. Because of its location between, the cytoplasmic and outer membranes, signals received and substrates bound are available, and transported across the cytoplasmic membrane using transport and signalling proteins, imbedded there (Fig.3.5)., Flagella: Many kinds of bacteria have slender, rigid, helical flagella (singular, flagellum), composed of the protein flagellin. These flagella range from 3 to 12 micrometers in length, and are very thin—only 10 to 20 nanometers thick. They are anchored in the cell wall and, help to spin or pulling the bacteria through the water like a propeller. The number and, position of flagella vary in bacteria. The arrangement may be monotrichous (a single polar, flagellum), lophotrichous (a cluster of polar flagella), amphitrichous (flagella at both the ends, either singly or in cluster), cephalotrichous (two or more flagella at one end of bacterial cell),, , UTTARAKHAND OPEN UNIVERSITY, , Page 75
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , peritrichous (cell surface evenly surrounded by several lateral flagella) or atrichous (cells, devoid of flagella)., A flagellum consists of three basic parts – the basal body, hook and filament. The basal body, attaches the flagellum to the cell wall and plasma membrane. It is composed of a small, central rod inserted into a series of rings. In gram positive bacteria, only a distal (inner) pair, of rings is present while in gram negative bacteria two pairs of rings (the proximal and distal), are connected by a central rod. The hook of the flagellum is present outside the cell wall and, connects filament to the basal body. It consists of different proteins. The hook of gram, positive bacteria is slightly longer than the gram negative bacteria. The outermost long part of, flagellum is called filament. It is made up of globular proteins called flagellin which are, arranged in several chains and form a helix around a hollow core (Fig.3.6)., , Fig.3.6- Structure of Bacterial flagella, , Pili (Fimbriae): These are other hair like structures that occur on the cells of some bacteria., They are shorter than bacterial flagella. They are .2 – 20 m long and about 7.5 to 10, nanometers thick (Fig.3.7). Pili help the bacterial cells attach to appropriate substrates and, exchange, , Fig.3.7- Bacteria showing structure of pili, , UTTARAKHAND OPEN UNIVERSITY, , Page 76
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , genetic information. Pili originate from cytoplasm. According to the function, pili are of two, types, (a) common pili which act to adhere the cell to the surface, (b) sex pili which join the, other bacterial cell for transfer of genome. These structures also affect the metabolic activity, of the bacterial cell. They are also equipped with antigen properties as they act as, thermolabile non-specific agglutinogen., , The Cell Interior, The most fundamental characteristic of bacterial cells is their prokaryotic organization., Bacterial cells lack the extensive functional compartmentalization seen within eukaryotic, cells., , Internal membranes: Many bacteria possess invaginated regions of the plasma membrane, that function in respiration or photosynthesis. These are called mesosomes. These structures, form the site for respiratory activity. The cytoplasmic membrane is also the site of many, metabolic activities, e.g. the organic and inorganic nutrients are transported by permeases, through plasma membrane. It consists of enzymes of biosynthetic pathways that synthesize, different components of cell wall, such as peptidoglycogen, techoic acid, phospholipids and, polysaccharides., The cytoplasm of bacterial cell is thick and semi-transparent. It lacks cytoskeleton and, cytoplasmic streaming compartmentation of cell organelles is absent in bacterial cell., Concentrated deposition of certain substances is dectectable in the cytoplasm of some, bacteria. The volutin granules are found in some bacteria which serve as reserve source of, phosphate. Another reserve carbon and energy source called polybeta-hydroxybutyrate is also, found in aerobic bacteria. In some bacteria that live in aqatic habitats, bright refractile bodies, which are hallow and have regular shape with more or less conical ends are observed by, electron microscopy. These are gas vacuoles which provide buoyancy., , Nucleoid region: Bacteria lack nuclei and do not possess the complex chromosomes, characteristic of eukaryotes. Instead, their genes are encoded within a single double-stranded, ring of DNA that is crammed into one region of the cell known as the nucleoid region. Many, bacterial cells also possess small, independently replicating circles of DNA called plasmids., Plasmids contain only a few genes, usually not essential for the cell‘s survival. They are best, thought of as an excised portion of the bacterial chromosome., , Ribosomes: Bacterial ribosomes are smaller than those of eukaryotes and differ in protein, and RNA content. Antibiotics such as tetracycline and chloramphenicol can be used to, observe the difference—they bind to the bacterial ribosomes and block protein synthesis, but, they do not bind to eukaryotic ribosomes. The ribosomes have two sub units, a larger 50 s sub, unit and a smaller 30 s sub unit. Each is composed of proteins and ribosomal RNA., , 3.4- CLASSIFICATION, Classification is done to describe the diversity of bacterial species by naming and grouping, organisms based on similarities. Bacteria can be classified on the basis of cell, structure, cellular metabolism or on differences in cell components such as DNA, fatty acids,, pigments, antigens and quinones. While these schemes allowed the identification and, UTTARAKHAND OPEN UNIVERSITY, , Page 77
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , classification of bacterial strains, it was unclear whether these differences represented, variation between distinct species or between strains of the same species. This uncertainty, was due to the lack of distinctive structures in most bacteria, as well as lateral gene, transfer between unrelated species. Due to lateral gene transfer, some closely related bacteria, can have very different morphologies and metabolisms. To overcome this uncertainty,, modern bacterial classification emphasizes molecular systematics, using genetic techniques, such as guanine/cytosine ratio determination, genome-genome hybridization, as well, as sequencing genes that have not undergone extensive lateral gene transfer, such as, the rRNA gene. Classification of bacteria is determined by publication in the International, Journal, of, Systematic, Bacteriology, and, Bergey's, Manual, of, Systematic, Bacteriology. The International Committee on Systematics Bacteriology (ICSB) maintains, international rules for the naming of bacteria and taxonomic categories and for the ranking of, them in the International Code of Nomenclature of Bacteria., The term "bacteria" was traditionally applied to all microscopic, single-cell prokaryotes., However, molecular systematic showed prokaryotic life to consist of two separate domains,, originally called Eubacteria and Archaebacteria, (now called Bacteria and Archaea) that, evolved independently from an ancient common ancestor. These two domains, along with, Eukarya, are the basis of the three domain system, which is currently the most widely used, classification system in microbiology. However, due to the relatively recent introduction of, molecular systematic and a rapid increase in the number of genome sequences that are, available, bacterial classification remains a changing and expanding field. For example, a few, biologists argue that the Archaea and Eukaryotes evolved from Gram-positive bacteria., Identification of bacteria in the laboratory is particularly relevant in medicine, where the, correct treatment is determined by the bacterial species causing an infection. Consequently,, the need to identify human pathogens was a major impetus for the development of techniques, to identify bacteria., , Fig.3.8- Phylogenetic tree showing the diversity of bacteria, compared to other, organisms. Eukaryotes are colored red, archae green and bacteria blue, UTTARAKHAND OPEN UNIVERSITY, , Page 78
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , The Gram stain, developed in 1884 by Hans Christian Gram, characterises bacteria based on, the structural characteristics of their cell walls. The thick layers of peptidoglycan in the, "Gram-positive" cell wall stain purple, while the thin "Gram-negative" cell wall appears pink., By combining morphology and Gram-staining, most bacteria can be classified as belonging, to one of four groups (Gram-positive cocci, Gram-positive bacilli, Gram-negative cocci and, Gram-negative bacilli). Some organisms are best identified by stains other than the Gram, stain, particularly mycobacteria or Nocardia, which show acid-fastness on Ziehl-Neelsen or, similar stains. Other organisms may need to be identified by their growth in special media, or, by other techniques, such as serology., Culture techniques are designed to promote the growth and identify particular bacteria, while, restricting the growth of the other bacteria in the sample. Often these techniques are designed, for specific specimens; for example, a sputum sample will be treated to identify organisms, that cause pneumonia, while stool specimens are cultured on selective media to identify, organisms that cause diarrhoea, while preventing growth of non-pathogenic bacteria., Specimens that are normally sterile, such as blood, urine or spinal fluid, are cultured under, conditions designed to grow all possible organisms. Once a pathogenic organism has been, isolated, it can be further characterised by its morphology, growth patterns, pattern of, hemolysis, and staining., As with bacterial classification, identification of bacteria is increasingly using molecular, methods. Diagnostics using such DNA-based tools, such as polymerase chain reaction, are, increasingly popular due to their specificity and speed, compared to culture-based, methods. These methods also allow the detection and identification of "viable but, nonculturable" cells that are metabolically active but non-dividing. However, even using, these improved methods, the total number of bacterial species is not known and cannot even, be estimated with any certainty. Following present classification, there are a little less than, 9,300 known species of prokaryotes, which includes bacteria and archaea; but attempts to, estimate the true number of bacterial diversity have ranged from 107 to 109 total species – and, even these diverse estimates may be off by many orders of magnitude (Fig.3.8)., , 3.5- NUTRITION, Bacteria exhibit an extremely wide variety of metabolic types. The distribution of metabolic, traits within a group of bacteria has traditionally been used to define their taxonomy, but, these traits often do not correspond with modern genetic classifications. Bacterial metabolism, is classified into nutritional group on the basis of three major criteria: the kind of energy used, for growth, the source of carbon, and the electron donors used for growth. An additional, criterion of respiratory microorganisms is the electron acceptors used for aerobic or anaerobic, respiration. Carbon metabolism in bacteria is either heterotrophic, where organic, carbon compounds are used as carbon sources, or autotrophic, meaning that cellular carbon is, obtained by fixing carbon dioxide., , UTTARAKHAND OPEN UNIVERSITY, , Page 79
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Nutritional types in bacterial metabolism, Nutritional, type, , Source of, energy, , Source of carbon, , Examples, , Phototrophs, , Sunlight, , Organic compounds, (photoheterotrophs) or carbon, fixation (photoautotrophs), , Cyanobacteria , Green sulfur, bacteria, Chloroflexi,, , Lithotrophs, , Inorganic, compounds, , Organic compounds, (lithoheterotrophs) or carbon, fixation (lithoautotrophs), , Thermodesulfobacteria and, Nitrospirae, , Organotrophs, , Organic, compounds, , Organic compounds, (chemoheterotrophs) or carbon, fixation (chemoautotrophs), , Bacillus and Clostridium, , Heterotrophic bacteria include parasitic types. Typical autotrophic bacteria are, phototrophic cyanobacteria (Fig.3.9), green sulfur-bacteria and some purple bacteria, many, chemolithotrophic species, such as nitrifying or sulfur-oxidising bacteria. Energy metabolism, of bacteria is either based on phototrophy, (the use of light through photosynthesis), or based, on chemotrophy, (the use of chemical substances for energy), which are mostly oxidised at, the expense of oxygen or alternative electron acceptors (aerobic/anaerobic respiration)., , Fig.3.9- Filaments of photosynthetic cyanobacteria, , UTTARAKHAND OPEN UNIVERSITY, , Page 80
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Bacteria are further divided into lithotrophs that use inorganic electron donors, and organotrophs that use organic compounds as electron donors. Chemotrophic organisms, use the respective electron donors for energy conservation (by aerobic/anaerobic respiration, or fermentation) and biosynthetic reactions (e.g., carbon dioxide fixation), whereas, phototrophic organisms use them only for biosynthetic purposes. Respiratory organisms, use chemical compounds as a source of energy by taking electrons from the reduced substrate, and transferring them to a terminal electron acceptor in a redox reaction. This reaction, releases energy that can be used to synthesise ATP and drive metabolism. In aerobic, organisms, oxygen is used as the electron acceptor. In anaerobic organisms other inorganic, compounds, such as nitrate, sulfate or carbon dioxide are used as electron acceptors. This, leads to the ecologically important processes of denitrification, sulfate reduction,, and acetogenesis, respectively., Another way of life of chemotrophs in the absence of possible electron acceptors is, fermentation, wherein the electrons taken from the reduced substrates are transferred to, oxidised intermediates to generate reduced fermentation products. Fermentation is possible,, because the energy content of the substrates is higher than that of the products, which allows, the organisms to synthesise ATP and drive their metabolism., These processes are also important in biological responses to pollution; for example, sulfate, reducing bacteria are largely responsible for the production of the highly toxic forms, of mercury in the environment. Non-respiratory anaerobes use fermentation to generate, energy and reducing power, secreting metabolic by-products as waste. Facultative, anaerobes can, switch, between, fermentation, and, different terminal, electron, acceptors depending on the environmental conditions in which they find themselves., Lithotrophic bacteria can use inorganic compounds as a source of energy. Common inorganic, electron donors are hydrogen, carbon monoxide, ammonia, ferrous iron and other reduced, metal ions, and several reduced sulfur compounds. In unusual circumstances, methane, gas can be used by methanotrophs bacteria as a source of electrons and a substrate for, carbon anabolism. In both aerobic phototrophy and chemolithotrophy, oxygen is used as a, terminal electron acceptor, whereas under anaerobic conditions, inorganic compounds are, used instead. Most lithotrophic organisms are autotrophic, whereas organotrophic organisms, are heterotrophic., In addition to fixing carbon dioxide in photosynthesis, some bacteria also fix nitogen gas, using the enzyme nitrogenase. This environmentally important trait can be found in bacteria, of nearly all the metabolic types listed above, but is not universal., Regardless of the type of metabolic process they employ, the majority of bacteria are able to, take in raw materials only in the form of relatively small molecules, which enter the cell by, diffusion or through molecular channels in cell membranes. It has recently been shown, that Gemmata obscuriglobus is able to take in large molecules via a process that in some, ways resembles endocytosis, the process used by eukaryotic cells to engulf external items., , Bacterial growth follows four phases. When a population of bacteria first enters a highnutrient environment that allows growth, the cells need to adapt to their new environment., UTTARAKHAND OPEN UNIVERSITY, , Page 81
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , The first phase of growth is the lag phase, a period of slow growth when the cells are, adapting to the high-nutrient environment and preparing for fast growth. The lag phase has, high biosynthesis rates, as proteins necessary for rapid growth are produced. The second, phase of growth is the log phase, also known as the logarithmic or exponential phase. The, log phase is marked by rapid exponential phase. The rate at which cells grow during this, phase is known as the growth rate (k), and the time it takes the cells to double is known as, the generation time (g). During log phase, nutrients are metabolised at maximum speed until, one of the nutrients is depleted and starts limiting growth. The third phase of growth is, the stationary phase and is caused by depleted nutrients. The cells reduce their metabolic, activity and consume non-essential cellular proteins. The stationary phase is a transition from, rapid growth to a stress response state and there is increased expression of genes involved, in DNA repair, antioxidant metabolism and nutrient transport. The final phase is the death, phase where the bacteria run out of nutrients and die., , 3.6- REPRODUCTION, Unlike in multicellular organisms, increases in cell size and reproduction by cell division are, tightly linked in unicellular organisms. Bacteria grow to a fixed size and then reproduce, through binary fission, a form of asexual reproduction. Under optimal conditions, bacteria, can grow and divide extremely rapidly, and bacterial populations can double as quickly as, every 9.8 minutes. In cell division, two identical clone daughter cells are produced. Some, bacteria, while still reproducing asexually, form more complex reproductive structures that, help disperse the newly formed daughter cells (Fig.3.10)., , UTTARAKHAND OPEN UNIVERSITY, , Page 82
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.3.10- Binary fission in bacteria, , DNA Transfer, Some bacteria transfer genetic material between cells. This can occur in three main ways., First, bacteria can take up exogenous DNA from their environment, in a process, called transformation. Genes can also be transferred by the process of transduction, when the, , UTTARAKHAND OPEN UNIVERSITY, , Page 83
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.3.11: Bacterial Transduction, , UTTARAKHAND OPEN UNIVERSITY, , Page 84
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.3.12: Bacterial conjugation in Bacillus, , integration of a bacteriophage introduces foreign DNA into the chromosome (Fig.3.11). The, third method of gene transfer is conjugation, whereby DNA is transferred through direct cell, contact (Fig.3.12)., Transduction of bacterial genes by bacteriophage appears to be a consequence of infrequent, errors during intracellular assembly of virus particles, rather than a bacterial adaptation., Conjugation, in the much-studied E. coli system is determined by plasmid genes, and is an, adaptation for transferring copies of the plasmid from one bacterial host to another. It is, seldom that a conjugative plasmid integrates into the host bacterial chromosome, and, subsequently transfers part of the host bacterial DNA to another bacterium. Plasmid-mediated, transfer of host bacterial DNA also appears to be an accidental process rather than a bacterial, adaptation., Transformation, unlike transduction or conjugation, depends on numerous bacterial gene, products that specifically interact to perform this complex process, and thus transformation is, clearly a bacterial adaptation for DNA transfer. In order for a bacterium to bind, take up and, recombine donor DNA into its own chromosome, it must first enter a special physiological, UTTARAKHAND OPEN UNIVERSITY, , Page 85
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , state termed competence. In Bacillus subtilis about 40 genes are required for the development, of competence. The length of DNA transferred during B. subtilis transformation can be, between a third of a chromosome up to the whole chromosome. Transformation appears to be, common among bacterial species, and thus far at least 60 species are known to have the, natural ability to become competent for transformation. The development of competence in, nature is usually associated with stressful environmental conditions, and seems to be an, adaptation for facilitating repair of DNA damage in recipient cells., In ordinary circumstances, transduction, conjugation, and transformation involve transfer of, DNA between individual bacteria of the same species, but occasionally transfer may occur, between individuals of different bacterial species and this may have significant consequences,, such as the transfer of antibiotic resistance. In such cases, gene acquisition from other, bacteria or the environment is called horizontal gene transfer and may be common under, natural conditions Gene transfer is particularly important in antibiotic resistance as it allows, the rapid transfer of resistance genes between different pathogens., , 3.7-ECONOMIC IMPORTANCE, Bacteria play important roles in different fields such as agriculture, industry etc. Some of, them are mentioned below:, , 3.7.1 Role in agriculture, a) Scavenging Role: Saprophytic bacteria obtain food from organic remains such as animal, excreta, fallen leaves, meat etc. They decompose these substances by action of digestive, enzymes aerobically or anaerobically (known as fermentation). Thus they help in sanitation, of nature, therefore also known as scavengers. e.g. Pseudomonas, b) Nitrification: Rhizobium bacteria, living in root nodules of leguminous plant, symbiotically,, helps, in, fixing, atmospheric, nitrogen., Similarly, Nitrosomanas and Nitrococcus convert ammonium salt to nitrites. Nitrites are, further changed to nitrates by Nitrobacter and Nitrocystis. It enables plants to uptake, nitrogen., c) Production of Organic Manure: As stated above, saprophytic bacteria help in breaking, of complex organic substance to simpler forms. Thus, in this process, they help to convert, farm refuse, dung and other wastes to manure., d) Preparation of Ensilage: Ensilage is preserved cattle fodder prepared by packing fresh, chopped fodder sprinkled with molasses. Fermentation activity of bacteria produces lactic, acid that acts as preservative in ensilage., e) Production of fuel: Bacteria, while converting animal dung and other organic wastes to, manure, help in production of fuel. Gober gas plant is an example of this process., f) Disposal of sewage: Bacteria help in disposal of sewage by decomposing it and thus, help, in environmental sanitation., , UTTARAKHAND OPEN UNIVERSITY, , Page 86
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 3.7.2 Role in industry, a) Dairy Industry: Bacteria such as Streptococcus lactis convert milk sugar lactose into, lactic acid that coagulates casein (milk protein). Then, milk is converted into curd, yoghurt,, cheese etc needed for the industry., b) Production of Organic Compounds: Fermentation (breakdown of carbohydrate in, absence of oxygen) process of various bacteria produces organic compounds like lactic acid, (by Lactobacillus), acetic acid (by Acetobacter aceti), acetone (by Clostridium, acetabutylicum) etc., c) Fibre Retting: The action of some bacteria like Clostridium, Pseudomonas etc. help in, fibre retting i.e. separation of stem and leaf fibre of plants from other softer tissue., d) Curing: The leaves of tea and tobacco, beans of coffee and coca are cured off their, bitterness with the help of action of certain bacteria such as Bacillus megatherium., e) Production of Antibiotics: Number of anti-bacterial and anti-fungal antibiotics such as, Hamycin, Polymyxin, Trichomycin etc are obtained from mycelia bacteria, (like Streptomyces). Similarly, Bacillus is used for production of antibiotics such as, Bacitracin, Gramicidin etc, f) Production of Vitamins: Different kinds of vitamins are produced from bacteria like, Riboflavin from Clostridium butylicum, Vitamin B12 from Bacillus megatherium and, Vitamin K and B-complex from Escherichia coli., , Harmful effects of bacteria, Though bacteria plays important role in agriculture, industries and natural sanitation etc, they, have some harmful effects also., a) Food Spoiling: Saprophytic bacteria always not only help in decomposition of dead, matters, but they also cause the rotting of vegetables, fruits, meat, bread etc., b) Food Poisoning: Bacteria like Staphylococcus aureus cause food poisoning and cause, diarrhoea and vomiting., c)Damaging of domestic articles: Spirochete cytophaga deteriorates cotton, leather and, wooden articles., d) Denitrification: Bacteria such as Thiobacillus and Microbacillusconvert nitrate of the soil, to the gaseous nitrogen. This hampers plant growth., e) Desulphurication: Bacteria such as Desulfovibrio convert soil sulphates into hydrogen, sulphide., f) Cause of Diseases: It is known that over 90% of human diseases and over 10% of plant, diseases are caused by bacteria., , 3.8- SUMMARY, Bacteria are microscopic unicellular prokaryotic organisms characterized by the lack of a, membrane-bound nucleus and membrane-bound organelles. Bacteria were the only form of, UTTARAKHAND OPEN UNIVERSITY, , Page 87
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , life on earth for 2 billion years. There are more bacteria, as separate individuals, than any, other type of organism; there can be as many as 2.5 billion bacteria are estimated in one gram, of fertile soil. Bacteria exhibit an extremely wide variety of metabolic types. The distribution, of metabolic traits within a group of bacteria has traditionally been used to define, their taxonomy, but these traits often do not correspond with modern genetic classifications., Unlike in multicellular organisms, increases in cell size and reproduction by cell division are, tightly linked in unicellular organisms. Bacteria grow to a fixed size and then reproduce, through binary fission, a form of asexual reproduction. In bacteria, DNA transfer occurs, through Conjugation, Transduction and Transformation. Bacteria are harmful as well as, economically important., , 3.9-GLOSSARY, Aerobe – An organism capable of living only in the presence of oxygen., Anaerobe – An organism capable of living in the absence of free oxygen., Chemotrophs- An organism that obtains the energy required for the synthesis of organic, molecules from the oxidation of organic compounds., Denitrification – The decomposition of nitrate from the surrounding through bacteria during, anaerobic respiration., Double Helix- A molecule composed of two complimentary polymeric chains coiled in the, same direction about in the same axis, as DNA., Growth – The sum total of the various physiological processes that combine to cause an, increase in size and dry weight., Metabolism – The net result of the biochemical processes of a living organism or cells., Pathogens – An organism able to cause disease. The term restricted to living organisms., Systematic – The scientific study of the classification of living things, with emphasis on their, evolutionary relationship., Taxonomy – The study of the principles and practices of classification of living things., , 3.10- SELF ASSESSMENT QUESTIONS, 3.10.1 Short answer questions, Q1 What are bacteria?, Ans. Bacteria are prokaryotic and unicellular beings. Bacteria have simple organization; they, have an external cell wall, plasma membrane, circular DNA within the cytoplasm and, ribosome for protein synthesis. Some bacteria are encapsulated, i.e., they have a, polysaccharide capsule outside the cell wall., Q2 Are bacteria the only prokaryotic beings?, Ans. Prokaryotic beings are classified into two big groups: archaebacteria and bacteria (also, known as eubacteria). Compared to bacteria, archaebacteria have basic differences, like the, chemical compositions of their plasma membrane and cell wall and different enzymes related, to DNA and RNA metabolism., Q3 What are halophile, thermoacidophile and methanogen archaebacteria?, UTTARAKHAND OPEN UNIVERSITY, , Page 88
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Ans. There are three peculiar types of archaebacteria. The halophile archaebacteria only, survive in salt-rich environments (even salinity of the sea is not enough for them)., Thermoacidophile archaebacteria are characterized by living under high temperatures and, low pH. The methanogen archaebacteria are those that liberate methane gas (CH4), they are, found in swamps., Q4 What are examples of human diseases caused by bacteria?, Ans. Some human diseases caused by bacteria are tuberculosis, pertussis, diphtheria,, bacterial meningitis, gonorrhea, syphilis, bubonic plague, leptospirosis, cholera, typhoid, fever, Hansen‘s disease, trachoma, tetanus, anthrax., Q5 How are bacteria classified according to their need for oxygen?, Ans. According to their necessity of oxygen bacteria are classified into anaerobic (those that, survive without oxygen) and aerobic (those that do not survive without oxygen)., Q6 According to their morphology how are bacteria classified?, Ans. Bacteria present different morphological patterns. A bacterium can be classified into, coccus, bacillus, vibrio or spirochete., , 3.10.2 Multiple choice questions, 1. The name bacteria was first given by:, (a) Pasteur, (b) Alexander, (c) Ehrenberg, (d) Robert Koch, 2. Bacteria are placed under:, (a) Ascomycetes, (c) Phycomycetes, , (b) Schizomycetes, (d) Myxomycetes, , 3. Bacteria are found everywhere except:, (a) Cold water, (b) Soil, (c) Boiled water, (d) Body of man, 4. The cell-wall of bacteria is made-up of:, (a) Polysaccharides, (b) Lipids, (c) Proteins, (d) All of the above, 5. The nucleus of bacteria is:, (a) Incipient, (c) Well defined, , UTTARAKHAND OPEN UNIVERSITY, , (b) Absent, (d) None of the above, , Page 89
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 6. Bacteria reproduce by:, (a) Fission, (c)Transduction, , BSCBO-101, , (b) Conjugation, (d) All of the above, , 7. Fertility of soil is increased by:, (a) Nitrogen fixing bacteria, (b) Denitrifying bacteria, (c) Heliminthosporium, (d) Saprolegnia, 8. Sometimes the bacterial cell is enclosed in a:, (a) Cell wall of cellulose, (b) Capsule, (c) Plasmalemma, (d) Cell membrane, 9. Cocci type of bacteria is:, (a) Flagellate, (c) Both types, , (b) Non-flagellate, (d) None of the above, , 10. Pneumonia is caused by:, (a) Virus, (c) Fungi, , (b) Bacteria, (d) Algae, , 11. Doctors usually boil their syringe and other surgical instruments before use to:, (a) Remove dust from them, (b) Clean them, (c) Sterilize them, (d) It is customary, , Answer key: 1(c), 2(b), 3(c), 4(d), 5(a), 6(d), 7(a), 8(b), 9(b), 10(b), 11(c), 3.10.3- Short answer questions, Q1 What are Bacteria? In how many classes we divide bacteria on the basis of morphology?, Describe with diagram., Q2 Describe the electron microscopic structure of bacterial cell., Q3 Discuss the economic importance of bacteria., Q4 Discuss the various mode of nutrition in the bacteria., Q5 Do bacteria affect the life of man? How?, , 3.11 REFERENCES, 1. Akamatsu T, Taguchi H (2001). "Incorporation of the whole chromosomal DNA in, protoplast lysates into competent cells of Bacillus subtilis". Biosci. Biotechnol., Biochem. 65(4): 823–9., 2. Bernstein H, Bernstein C, Michod RE (2012). "DNA repair as the primary adaptive, function of sex in bacteria and eukaryotes". Chapter 1: pp. 1–49 in: DNA Repair:, , UTTARAKHAND OPEN UNIVERSITY, , Page 90
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , New Research, Sakura Kimura and Sora Shimizu (eds.). Nova Sci. Publ., Hauppauge,, N.Y.ISBN 978-1-62100-808-8., 3. Bickle TA, Krüger DH (1993). ―Biology of DNA restriction‖. Microbiol., Rev. 57 (2): 434–50., 4. Brüssow H, Canchaya C, Hardt WD (2004). ―Phages and the evolution of bacterial, pathogens: from genomic rearrangement to lysogenic conversion‖. Microbiology and, Molecular Biology Reviews 68 (3): 560–602., 5. Chen I, Dubnau D (2004). "DNA uptake during bacterial transformation". Nature, Reviews Microbiology 2 (3): 241–9 Solomon JM, Grossman AD (1996). "Who's, competent and when: regulation of natural genetic competence in bacteria". Trends, Genet. 12 (4): 150–5., 6. Davison J (1999). "Genetic exchange between bacteria in the, environment". Plasmid 42(2): 73–91., 7. Hastings PJ, Rosenberg SM, Slack A (2004). "Antibiotic-induced lateral transfer of, antibiotic resistance". Trends Microbiol 12 (9): 401–4., 8. Johnsborg O, Eldholm V, Håvarstein LS (2007). "Natural genetic transformation:, prevalence, mechanisms and function". Res. Microbiol. 158 (10): 767–78., 9. Michod RE, Bernstein H, Nedelcu AM (2008). ―Adaptive value of sex in microbial, pathogens‖. Infect. Genet. Evol. 8 (3): 267-85., 10. Saito Y, Taguchi H, Akamatsu T (2006). "Fate of transforming bacterial genome, following incorporation into competent cells of Bacillus subtilis: a continuous length, of incorporated DNA". J. Biosci. Bioeng. 101 (3): 257–62., , 3.12- SUGGESTED READINGS, , , A Text Book of Microbiology: Dr. R.C. Dubey and Dr. D.K. Maheshwari(1999)., , , , Text Book of Biotechnology: H.K. Dass (2004)., , , , Microbiology: L.M. Prescott (2002)., , 3.13-TERMINAL QUESTIONS, Q1- What are bacteria? Describe in detail the economic importance of Bacteria., Q2- Explain in detail the reproduction in Bacteria., Q3- Give a detail note on bacterial cell with a well labelled diagram., Q4-Differentiate between Gram positive and Gram negative bacteria., Q5-Write a detailed note on Bacterial conjugation., , UTTARAKHAND OPEN UNIVERSITY, , Page 91
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-4- GENERAL ACCOUNT, CLASSIFICATION,, STRUCTURE, REPRODUCTION AND ECONOMIC, IMPORTANCE OF VIRUSES, 4.1- Objectives, 4.2-Introduction, 4.3-General account, 4.4-Classification, 4.5- Structure, 4.6-Reproduction, 4.7-Economic Importance, 4.8- Summary, 4.9- Glossary, 4.10- Self assessment question, 4.11-References, 4.12-Suggested Readings, 4.13-Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 92
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 4.1- OBJECTIVES, After reading this unit student will be able:, To study the structure of viruses., To learn the characteristic features of viruses., To know different shapes and types of viruses., To know economic importance of viruses., , 4.2-INTRODUCTION, “NEVER UNDERESTIMATE THE POWER OF A MICROBE”, Viruses are no longer considered the simplest form of life. Viruses are a unique group of, infectious agents whose distinctiveness resides in their simple, acellular organization and, pattern of reproduction. Viruses are simple, acellular entities consisting of one or more, molecules of either DNA or RNA enclosed in a coat of protein (and sometimes, in additional,, substances such as lipids and carbohydrates). They can reproduce only within living cells and, are obligately intracellular parasites. In simple words, we can say that these are simple, obligate parasites comprising of nucleic acid (DNA or RNA) and protein coat. Despite their, simplicity in comparison to cellular organisms, viruses are extremely important and deserve, close attention. The study of viruses has contributed significantly to the discipline of, molecular biology., Although in ancients times, people did not understand the nature of their illnesses, they were, acquainted with diseases, (such as rabies), which are now known to be viral in origin., In fact, there is some evidence that the great epidemics of 165 to 180 A.D. and 251 to, 266 A.D., (which severely weakened the Roman Empire and aided its decline), may, have been caused by measles and smallpox viruses. Hernán Cortés‘s conquest of the, Aztec Empire in Mexico was made possible by an epidemic that ravaged Mexico City., The virus was probably brought to Mexico in 1520 by the relief expedition sent to join, Cortés., The term virus was derived from a latin word virus means venom of poisonous fluid., All the causative agents of infectious diseases were put together under this category by, L. Pasteur., The discovery of Chamberland-Pasteur filter in 1884 by Charles Chamberland (a, collaborator of L. Pasteur) made possible the discovery of viruses. In 1885 Adolph, Mayer (a Dutch scientist) and in 1892 D.J. Ivanowsky (a Russian scientist) recognized, some microbes responsible for the occurrence of tobacco mosaic disease. The basic, criterion of their distinction from other familiar microbial agents was their ability to, pass through bacteria-proof filters and the agents were named as filterable viruses., The distinction of viruses from other cellular organisms was demonstrated by M.W., Beijerinck (a Dutch bacteriologist) in 1898. During his experiment he discovered that, TMV could be precipitated from an alcohol suspension without losing its infectious, ability and the fluid was capable of diffusing through agarose gel. These characteristics, were not possessed by bacteria or any other living entity. On the basis of these findings, UTTARAKHAND OPEN UNIVERSITY, , Page 93
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , , , BSCBO-101, , Beijerinck led to the conclusion that fluid itself was living and put forward the principle, of"Contagium vivum fluidum"( infectious living fluid)., In 1898 Friedrich Loeffer and Paul Frosch concluded that foot and mouth disease of, cattle was caused by a filterable virus rather than a toxin., In 1935 the structure of virus was studied by Wendelll M. Stanley. According to Him,, A virus is not simply a protein but a nucleoprotein and its infectious principle is the, nucleic acid rather than protein. For this discovery Stanley was awarded Nobel Prize, in 1946., F.W.Twort in 1915 and Felix d'Herelle in 1917 discovered that a virus was capable of, lysing bacterial cells. such viruses were designated as bacteriophage., In 1953 Luria described viruses as submicroscopic entities capable of being introduced, into specific living cells and reproducing inside such cells only., , 4.3-GENERAL ACCOUNT, , , Viruses cause many diseases of international importance. Amongst the human viruses,, smallpox, polio, influenza, hepatitis, human immunodeficiency virus (HIV-AIDS),, measles and the SARS corona virus are particularly well known., , , , While antibiotics can be very effective against diseases caused by bacteria, these, treatments are ineffective against viruses., , , , Since ancient times, there have been documented reports of river waters having the, ability to cure infectious diseases, such as leprosy. In 1896, Ernest Hanbury Hankin, reported that something in the waters of the Ganges and Yamuna rivers in India had, marked antibacterial action against cholera and could pass through a very fine, porcelain filter., , , , In 1915, British bacteriologist Frederick Twort, superintendent of the Brown, Institution of London, discovered a small agent that infected and killed bacteria. He, believed that the agent must be one of the following:, , , , a stage in the life cycle of the bacteria;, , , , an enzyme produced by the bacteria themselves; or, , , , a virus that grew on and destroyed the bacteria., , , , Control measures rely on vaccines (antibodies raised against some component of the, virus) or relief of the symptoms to encourage the body's own defense system., , , , Viruses also cause many important plant diseases and are responsible for huge losses, in crop production and quality in all parts of the world., , , , Infected plants may show a range of symptoms depending on the disease but often, there is leaf yellowing (either of the whole leaf or in a pattern of stripes or blotches),, leaf distortion (e.g. curling) and/or other growth distortions (e.g. stunting of the whole, plant, abnormalities in flower or fruit formation)., , UTTARAKHAND OPEN UNIVERSITY, , Page 94
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 4.4-CLASSIFICATION, Due to the ultramicroscopic size, presence of both living and non-living features and absence, of fossil records it is very difficult to classify viruses. On the basis of their host range,, clinical, epidemiological and pathological symptoms viruses are classified into following four, groups:, , 1. Plant viruses: These viruses infect only plants and depending on host they have been, subdivided into bacterial viruses, algal viruses, fungal viruses etc., 2. Invertebrate viruses: These infect invertebrates., 3. Vertebrate viruses: These infect vertebrate animals., 4. Dual-host viruses: These viruses infect two different hosts mentioned above., Holmes in 1948 included all viruses in a single order Virales having three suborders:, 1. Phagineae: This suborder includes bacteriophages., , 2. Phytophagineae: This suborder includes viruses infecting plants., 3. Zoophaginea: This suborder includes viruses infecting animals., , 4.5 STRUCTURE, Due to the realization of importance of viruses and their simple structure of viruses, the, morphology has been studied over decades and progress has been achieved from the use of, several modern techniques- X-ray diffraction, immunology, SEM, TEM, biochemical, analysis and electron microscopy.A simple virus particle is often termed as virion,, comprising of nucleic acid core of genetic material, enclosed within protein coat.The amount, of protein in viruses varies from 60-95% (Fig.4.1)., , 4.5.1 Size:, In recent times the size of virus was determined by using filtration technique through, collodion membrane of known porosity but now with the advancement of technology, ultracentrifugation and electron microscopy are employed. The size varies from 10 to 300 or, 400 nm. The smallest viruses are entero viruses, which are less than 30nm in diameter. The, largest are orthopox viruses, measuring about 240nm×300nm, i.e. approximately 1/10 the, size of red blood cell. The bacteriophages are about 65nm×200nm., , 4.5.2 Nucleic acid:, The viruses contain a nucleic acid core of genetic material which may b either DNA or RNA., The viruse containing DNA are termed as Deoxyviruses and those having RNA are termed as, Riboviruses. Generally,, I) All plant viruses have single stranded RNA., II) Animal viruses have either single or double stranded (rarely) RNA or double stranded, DNA., , UTTARAKHAND OPEN UNIVERSITY, , Page 95
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , III) Bacterial viruses contain mostly double stranded DNA but can also have single stranded, DNA or RNA., IV) Most of the insect viruses contain RNA but only a few have DNA., The number of nucleotide pairs in a molecule varies from 1,000 - 250,000 pairs but the, number of pairs in a specific virion is always constant., , 4.5.3- The protein coat:, The nucleic acid core is enclosed by a protective protin sheath called the capsid. Each, capsid consists of several identical protein subunits, known as capsomeres. The proteins may, be of single or several types. The number of proteins and the arrangement of capsomeres are, characteristic feature of viruses and thus can be useful in their identification and, classification. The capsomeres may be in the form of pentamer or hexamer., In some complex forms (e.g., influenza and herpes virus) the capsid is covered by an, envelope. It usually consists of some combination of lipids, protein and carbohydrates., Envelope of many viruses has projections called spikes, responsible for attachment with host., , COMPLEX STRUCTURE, , SIMPLE STRUCTURE, , ENVELOPED VIRUS, Fig.4.1 Structure of Virus, , 4.5.4. Bacteriophage, Viruses which infect bacterial cells are known as bacteriophage or viruses of bacteria., Bacteriophages were first observed in 1915 by F. Twort in England and in 1917 by, F.d'Herelle in France. D' Herelle used the term bacteriophage (eaters of bacteria)., Bacteriophages are found in all habitats where bacteria can survive and live as obligate, parasites. They are found in soil, fruits, sewage water, milk, vegetables and root nodules of, legumes. Some phages have also been found in the intestine of birds and animals. In human, beings, phages can be found intestine, urine, blood, saliva, pus and nasal exudate (Fig.4.2)., , UTTARAKHAND OPEN UNIVERSITY, , Page 96
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.4.2 Diagram of a typical tailed bacteriophage structure, , A bacteriophage is a virus that infects bacteria. The term is commonly shortened to, phage., Bacteriophages are similar to viruses that infect eukaryotes (plants, animals, and, fungi) in that there are many different kinds of structures and functions. These are, typically made of an outer protein hull that has genetic material inside it. The genetic, material can be ssRNA, dsRNA, ssDNA, or double-stranded DNA between 5 and 500, kilo base pairs long with either circular or linear arrangement., Bacteriophages are usually between 20 and 200 nanometers in size., Phages are ubiquitous in the environment, and humans are routinely exposed to them, at high levels through food and water without adverse effect., , Fig.4.3: T4 Bacteriophage, , 4.5.5-Types of phages, 1. T-phages (T1-T7; T standing for type):, These are characterized by the presence of a tail and exhibit the largest groups of phages, having ds DNA.T-phages have been divided into following three sub-groups i) T-even phages (T2, T4 and T6)., ii) T-odd phages (T1, T3 and T7)., , UTTARAKHAND OPEN UNIVERSITY, , Page 97
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 2. Virulent and temperate phages: As we know, viruses for microorganisms are called, phages and those for bacteria are bacteriophages. A virus can be thought of as genetic, elements within a protein coating. When injected into a cell, this genetic material may alter, the host so that its energy and metabolism are directed entirely toward making more virus, particles, and ultimately the host cell dies. Some phages are always actively seeking cells in, which to reproduce. Other phages can attach to the bacterial chromosome and remain passive, for a long time. Active phages are called virulent. The passive ones are called temperate, or lysogenic; they may become virulent if the system is shocked by an event such as a, temperature or pH change, but some host cells survive and continue to multiply. When not in, their virulent stage, temperate phages have no discernable effect on their hosts., T4 is one of many virulent phages that infect E. coli. Its sheath fastens to the cell wall, and, constriction forces some phage DNA (some phages are RNA) into the cell to make it into a, factory for making more phage particles (Fig.4.3)., , 4.5.6 Structure of Bacteriophage, As the bacteriophages cannot be separated by bacterial filters, their structural details are, known through electron microscopic studies of some larger particles (T-even group) which, infect bacterium E. coli. The appearance of phage resembles a tadpole or spermatozoid; it is, differentiated into a head and a tail. The head may be prismoid (T, T2, T6) or hexagonal (T3, and T7) The phages which are filamentous do not show differentiation into head and tail. The, size of head is approximately 950Å× 650Å. The extended part between head and the tail is, called collar. The tail is equal to the length of the head and has a diameter of 80Å. At the, proximal end of tail a hexagonal end plate is present which is approximately 200Å thick, having 6 tail pins (fibreson) in its under surface (the size of each is about 1500Å). The tail, pins help in adsorption of phage particle on the surface of the bacterium and the enzymes, secreted by tail pins are responsible for the lysis of bacterial cell wall., , Chemical composition, Bacteriophages contain protein -50 to 60 % ; nucleic acids (either DNA or RNA) 40 to 50 %, some lipids ; Head wall - 2,000 similar subunits of proteins ; molecular wt of phage DNA 2,500,000., , 4.6 REPRODUCTION, Replication, Although the basic mechanism of penetration and multiplication is similar in all the viruses,, the process is best studied in bacteriophages. These multiply by two alternate methodsI. Lytic cycle., II. Lysogenic cycle., , 4.6.2: Lytic cycle, T-even bacteriophages multiply by lytic cycle. This cycle involves following four steps i. Infection, UTTARAKHAND OPEN UNIVERSITY, , Page 98
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , ii. Synthesis of phage components in the host cells., iii. Assembly of new phage particle., iv. Liberation of phage particles from the host cells., , i. Infection:, The infection starts with adsorption of the phage on the host bacterium with the help of its tail, fibres and transfer of phage nucleic acid into host cell. The adsorption depends on the mutual, affinity of the phage and bacterium. Some phages infect a particular bacterium and others, adsorb themselves at a specific site only (receptor site)., , ii. Synthesis of phage components in the host cell:, Inside the bacterial cell, the phage nucleic acid takes over the protein synthesis machinery of, the cell. It suppresses the bacterial protein and directs the metabolism of the cell to synthesize, the proteins of phage particle. This is accomplished by the synthesis of viral specific m-RNA, which later directs the host cell to synthesize proteins which are used as subunits of the, protein coat of the phage particle. These proteins are called late proteins. Towards the end of, replication of phage nucleic acid, a late protein, called phage lysozyme is synthesized., , iii. Assembly of new phage particle:, Assembly of nucleic acids and proteins (late proteins) into new phage particles is called, maturation. This process is controlled by viral genome. It includes condensation of nucleic, acid in crystalline form, aggregation of protein subunits around DNA to form head,, attachment of core tube with tail plate, attachment of tail with head and attachment of tail, fibres to the end plate., , iv. Liberation of phage particles from the host cells:, Lysis of the host cell is essential for the liberation of phage particles. It is facilitated by the, lysozyme secreted by the phage DNA in the host celll. The host cell ruptures as a result of, lysis and the phage particles are liberated., The entire cycle of phage development is completed in 30-90 minutes. In an infected, bacterium 7-8 phage particles are formed per minute and a total of about 200 phages are, formed in a bacterium (Fig.4.4)., , UTTARAKHAND OPEN UNIVERSITY, , Page 99
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.4.4: Lytic Cycle of T4 Bacteriophage, , 4.6.2. Lysogenic cycle:, Some phages do not cause lysis of host cell and exhibit lysogenic cycle. Phages multiplying, by this method are known as lysogenic phages or temperate phages and participating host, cells are called lysogenic cells. The phage injects its DNA into host cell. The linear phage, DNA becomes circular and integrates within the bacterial chromosome by recombination., The inserted phage DNA is now called prophage. The activity of prophage genes is repressed, by two repressor proteins which are synthesized by phage genes. This checks the synthesis of, new phages within the host cell. Each time bacterial cell divide, the prophage multiplies, along with bacterial chromosome. The prophage remains latent within the progeny cells (Fig., 4.5)., , Fig.4.5: Lysogenic life cycle of Lamda (ƛ) phage, UTTARAKHAND OPEN UNIVERSITY, , Page 100
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 4.7 ECONOMIC IMPORTANCE, Viruses are entities which infect all cellular forms eukaryotes (vertebrate animals,, invertebrate animals, plants, fungi) and prokaryotes (bacteria and archaea). They are obligate, parasites and reproduce only in living organisms. Therefore these organisms are very, important and we need to understand the nature of viruses, how they replicate and how they, cause disease. This knowledge permits the development of effective means for prevention,, diagnosis and treatment of virus diseases through the production of vaccines, diagnostic, reagents and techniques, and antiviral drugs. These medical applications constitute major, aspects of the science of virology., , 4.7.1 Negative impacts of viruses:, Veterinary virology and plant virology are also important because of the economic impact of, many viruses that cause disease in domestic animals and crop plants: foot and mouth disease, virus and rice yellow mottle virus are just two examples. Another area where viruses can, cause economic damage is in the dairy industry, where phages can infect the lactic acid, bacteria that are responsible for the fermentations that produce cheese, yogurt and other milk, products. Viruses are important agents of many human diseases, ranging from the trivial (e.g., common colds) to the lethal (e.g. rabies), and viruses also play roles in the development of, several types of cancer. Virus diseases can also affect the well-being of societies. Smallpox, had a great impact in the past and AIDS is having a great impact today., , Different viral diseases attack different parts of the body, S.NO., , Viruses, , Target parts/organisms, , Source of spread, , 1, , Chicken virus and, measles virus, , Cells of skin causing watery, blisters and red rashes., , Direct or indirect contact, , 2, , Influenza virus, , Lining of nose and throat, , Spread through direct contact,, Spitting and coughing, , 3, , Polio virus, , Muscles, , Infected faeces and flies, , 4, , HIV virus, , Immune system, , Direct and sexual contact with, an infected person., , 5, , Tobacco mosaic, virus, , Tobacco plant, , Direct contact, , 4.7.2-Positive impact of viruses:, Phage typing of bacteria: Some groups of bacteria, such as certain Salmonella, species, are classified into strains on the basis of the spectrum of phages to which they, are susceptible. Identification of the phage types of bacterial isolates can provide, useful epidemiological information during outbreaks of disease caused by these, bacteria., , UTTARAKHAND OPEN UNIVERSITY, , Page 101
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Sources of enzymes: A number of enzymes used in molecular biology are virus, enzymes. Examples include reverse transcriptases from retroviruses and RNA, polymerases from phages., Pesticides: Some insect pests are controlled with baculo viruses and myxoma virus is, used to control rabbits., Anti-bacterial agents: In the mid-20th century phages were used to treat some, bacterial infections of humans. Interest declined with the discovery of antibiotics, but, has been renewed with the emergence of antibiotic-resistant strains of bacteria, Anti-cancer agents: Genetically modified strains of viruses, such as herpes simplex, virus and vaccinia virus, are being investigated for treatment of cancers. These strains, have been modified so that they are able to infect and destroy specific tumor cells, and, unable to infect normal cells., Gene vectors for protein production: Viruses such as certain baculo viruses and, adenoviruses are used as vectors to take genes into animal cells growing in culture., This technology can be used to insert into the cells genes encoding useful proteins,, such as vaccine components, and the cells can then be used for mass production of the, proteins., Gene vectors for treatment of genetic diseases: Children with severe combined, immunodeficiency (baby in the bubble syndrome) have been successfully treated, using retroviruses as vectors to introduce into their stem cells a non-mutated copy of, the mutated gene responsible for the disease., , 4.7.3- Viroids, , , , , , , , , These are pathogenic agents in plants., They show unencapsidated naked small circular RNA molecules, and are a few, hundred nucleotides long, with high degree of secondary structure., They lack the protein coat of viruses., These organisms do not code for any protein., They replicate in the nuclei of infected cells., Viroids rapidly move from cell to cell and through the phloem., They can be readily transmitted mechanically in the field, by vegetative, propagation, and some by pollens and seeds., , 4.8 SUMMARY, , , , Viruses are simple, acellular entities consisting of one or more molecules of either, DNA or RNA enclosed in a coat of protein (and sometimes, additional, substances, such as lipids and carbohydrates)., A simple virus particle is often termed as virion, comprising of nucleic acid core of, genetic material, enclosed within protein coat. The amount of protein in viruses varies, from 60-95%., , UTTARAKHAND OPEN UNIVERSITY, , Page 102
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , , , , BSCBO-101, , The viruses contain a nucleic acid core of genetic material which may b either DNA, or RNA. The viruses containing DNA are termed as Deoxyviruses and those having, RNA are termed as Riboviruses., The nucleic acid core is enclosed by a protective protein sheath called the capsid., Each capsid consists of several identical protein subunits, known as capsomeres. The, proteins may be of single or several types. The number of proteins and the, arrangement of capsomeres are characterstic feature of viruses and thus can be useful, in their identification and classification., These multiply by two alternate methodsLytic cycle, Lysogenic cycle., Viruses are on the borderline between living and non-living things. They show a, varied range of shapes. They may be spherical - (such as the adenovirus and, influenza virus), Rod like – (such as the tobacco mosaic virus) or many – sided, (such as bacteriophages), , The structure of Virus is very simple. There is just a core of DNA surrounded, by a sheath of Protein. There is no cytoplasm, nucleus or cell membrane., Viruses are not free living. They grow and multiply only in living cells., The reproduction of Virus is one characteristic which they share with living, organisms, but they reproduce only within another living cell. Outside a living, system the viruses neither reproduce nor respire., , Viruses cause various diseases in a specific host like plant, animal or in, bacteria. Viruses which attack bacteria and infect bacterial cells are known as, bacteriophage. They destroy the host cells by reproducing within them., , 4.9 - GLOSSARY, Nucleic acids: Nucleotides + phosphate + sugar., Obligate parasite: An obligate parasite, or holoparasite, is a parasitic organism that cannot complete, its life-cycle without exploiting a suitable host., SEM: Scanning electron microscope., TEM: Transmission electron microscopy., Unencapsidated: Not encapsulated., , UTTARAKHAND OPEN UNIVERSITY, , Page 103
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 4.10 SELF ASSESSMENT QUESTIONS, 4.10.1 Very short answer type questions, Q1. Which genetic material is found in all plant viruses?, Q2. Who discovered bacteriophages?, Q3. Define viroids?, Q4. What is the name of protein coat in viruses?, Q5. Mention the type of genetic material in most of the animal viruses?, Q6. What is the name of the subunit of the protein coat in viruses?, Q6. Name the two explicative cycles of bacteriophages?, Q7. What are bacteriophages?, , 4.10.2 Multiple choice questions, 1. The fact which supports the idea that viruses are living is that they:, (a) duplicate themselves, (b) penetrate plasma membrane, (c) can be crystallized, (d) are made of protein and DNA, 2. Bacteriophages were discovered by:, (a) Griffith, (c) Twort, , (b) Subramanian, (d) none of the above, , 3. Which one of the following is bacterium eater?, (a) Coliphage, (c) Cyanophage, , (b)bacteriophage, (d) TMV, , 4. Outer layer of viruses is composed of:, (a) Fats, (c) Carbohydrate, , (b) Protein, (d) Nucleic acid, , 5. Who discovered TMV?, (a) Bawden, (c) Stanley, , (b) Iwanowski, (d) Twort and d'Herelle, , 6. Genetic material in a bacteriophage is :, (a) RNA, (c) both DNA and RNA, , (b) DNA, (d) neither DNA nor RNA, , 7. Viruses synthesize their protein coats:, (a) inside the host cell, (c) both outside as well as inside the host cell, , (b)outside the host cell, (d) none of these, , UTTARAKHAND OPEN UNIVERSITY, , Page 104
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 8. Who isolated the plant viruses first?, (a) W.M Stanley, (c) D.Iwanowsky, , BSCBO-101, , (b) E.C Stakman, (d) K.M Smith, , 9. Which of the following is the constituent of a bacteriophage?, (a) protein, (b) DNA, (c) nucleoprotein, (d) lipid and protein, 10. Which of the following is the correct answer?, (a) a virion is a fully developed virus particle, (c) a virion is a capsomere, , (b) a virion is a capsid, (d) none of the above, , 4.10.2 ANSWERS KEYS:, 1. (a), 2.(c), 3. (b), 4. (b), 5. (b), 6. (b), 7. (a), 8.(c), 9.(c), 10.(a), , 4.11 REFERENCES, , , , , , , , , , , , , , Barton ES, White DW, Cathelyn JS, et al.. Herpesvirus latency confers symbiotic, protection from bacterial infection. Nature. 2007;447(7142):326–9., Bertoletti A, Gehring A. Immune response and tolerance during chronic hepatitis B virus, infection. Hepatol. Res.. 2007;37 Suppl 3:S331–8., Fowler MG, Lampe MA, Jamieson DJ, Kourtis AP, Rogers MF. Reducing the risk of, mother-to-child human immunodeficiency virus transmission: past successes, current, progress and challenges, and future directions. Am. J. Obstet. Gynecol.. 2007;197(3, Suppl):S3–9., Garnett GP. Role of herd immunity in determining the effect of vaccines against sexually, transmitted disease. J. Infect. Dis.. 2005;191 Suppl 1:S97–106., Nguyen VT, McLaws ML, Dore GJ. Highly endemic hepatitis B infection in rural, Vietnam.Journal of Gastroenterology and Hepatology. 2007;22(12):2093–100., Platonov AE. (The influence of weather conditions on the epidemiology of vector-borne, diseases by the example of West Nile fever in Russia). Vestn. Akad. Med. Nauk SSSR., 2006;(2):25–9. Russian., Rodrigues C, Deshmukh M, Jacob T, Nukala R, Menon S, Mehta A. Significance of HBV, DNA by PCR over serological markers of HBV in acute and chronic patients. Indian, journal of medical microbiology. 2001;19(3):141–4., Sauerbrei A, Wutzler P. The congenital varicella syndrome. Journal of perinatology :, official journal of the California Perinatal Association. 2000;20(8 Pt 1):548–54., Whitley RJ, Roizman B. Herpes simplex virus infections. Lancet. 2001;357(9267):1513–, 8., , 4.12 SUGGESTED READINGS, , , A Textbook of Microbiology by R.C. Dubey and D.K. Maheshwari. S. Chand, Company Limited., , UTTARAKHAND OPEN UNIVERSITY, , &, , Page 105
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , BSCBO-101, , Microbiology by P.D. Sharma. Rajpal and Sons Publishing., Microbiology. By Joseph Pelczar, Roger Delbert Reid, Eddie Chan Sun Chan, Mc Graw, Hill., Microbiology: An Introduction By Tortora, G.J., Funke, B.R., Case, C.L. Pearson, Benjamin Cummings, U.S.A. 10th edition., , 4.13 TERMINAL QUESTIONS, Q1. Give an illustrated account of the morphology and chemical structure of viruses?, Q2. Write an essay on the transmission of viruses?, Q3. What are bacteriophages?, Q4. Describe the structure of bacteriophage with the help of suitable diagrams?, Q5. Describe the different cycles seen during the replication of bacteriophages?, Q6. Write an essay on economic importance of viruses?, , UTTARAKHAND OPEN UNIVERSITY, , Page 106
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , BLOCK-2-FUNGI AND LICHENS, , UTTARAKHAND OPEN UNIVERSITY, , Page 107
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-5-CHARACTERS, ECONOMIC IMPORTANCE,, CLASSIFICATION AND GENERAL ACCOUNT OF, MAJOR CLASSES OF FUNGI, 5.1-Objectives, 5.2-Introduction, 5.3-General characters, 5.4-Classification (Ainsworth), 5.5-General account of major classes of Fungi, 5.6-Economic importance, 5.7-Summary, 5.8- Glossary, 5.9- Self assessment question, 5.10-References, 5.11-Suggested Readings, 5.12-Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 108
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 5.1 OBJECTIVES, After reading this unit student will be able:, , , , To study the range of thallus structure, various types of fungal tissues and specialized, vegetative and reproductive structures., To get familiarized with the general characters on with the classification is based., , , , To study the fungi ―as friends as well as foes‖., , 5.2 INTRODUCTION, Man‘s interest in fungi started with the observation of the beautiful, umbrella shaped, mushrooms and toad stools growing on soils forming fairy rings. The fungi (sing., fungus), are a distinct group of organisms that belong to lower plants. The name of the fungi derived, from the most obvious representatives, the mushrooms (Greek- mykes, Latin- fungus). They, are eukaryotes and share with plants the possession of a cell wall, liquid filled intracellular, vacuoles, microscopically visible streaming of the cytoplasm and lack of motility. However,, they do not contain photosynthetic pigments and are chemo-organotrophs. Most of them, grow aerobically and obtain their energy by oxidation of organic substances. Compared to the, plants, which are organized into stems, roots and leaves, fungi show only very limited, morphological differentiation and practically no functional differentiation., Fungi are diverse organisms. There are approximately 70,000 known species of fungi (and, probably 10 to 20 times more undiscovered species). These are found in such varied, environments as tropical forests, oceans and deserts. But they are primarily terrestrial, heterotrophic organisms; their principle role being the decomposition of organic matter along, with bacteria. Because they most often live on nonliving organic matter, hence called, saprophytes (Greek: sapros-rotten, phyton- plant). The products released by the decaying, action of fungi from their metabolism of organic matter are returned to the environment to be, used once again by other organisms. Some fungi are parasites and often pathogens of plants, and animals., The fungi are of great economic importance on account of their both harmful as well as, beneficial effects. A large number of fungi cause destructive havoc to our valuable crop and, timber plants, various lines of food products. They also attack the live-stock as well as human, beings. But, all of them are not harmful to the mankind, as most of the species bring about, decomposition of dead bodies of plants and animals as well as of animal dung. In addition, they are also useful in the production of new age medicines and other useful products., , 5.3 GENERAL CHARACTERS, Thallus structure, Unicellular thallus – In some of the lower fungi such as Chytrids the thallus is more or, less a spherical, single celled structure. At the time of reproduction it becomes a reproductive, UTTARAKHAND OPEN UNIVERSITY, , Page 109
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , unit. The latter produces the asexual or sexual cells. Such fungi are called holocarpic. In this, type of fungi vegetative and reproductive phases do not occur together in the same thallus., Plasmodiophora has a vegetative phase consisting of a naked multinucleate, amoeboid mass, of protoplasm. It is termed plasmodium. In the unicellular holocarpic forms, the mycelium is, absent e.g. Synchytrium. Most nonmycelial fungi as Olphidium and Yeasts are basically, unicellular with a true cell wall. In Yeast it is common to find unicellular thalli producing bud, cells in succession. These bud cells may remain attached to one another in an easily, dissociated chain. Such a chain of bud cells is referred to as pseudomycelium., , Filamentous thallus – In most true fungi, the thallus is filamentous composed of Hyphae., Loosely aggregated hyphae are collectively forms a network known as mycelium. The, hyphae may be hyaline or variously coloured. Each hypha may vary in overall length and, diameter, the latter ranging from 0.5 to 1mm. The apex of hyphae is a thin walled region, where growth materials are added, differentiation takes place, elongation occurs in a zone, behind the tip. Branching of hyphae is dichotomous when the apex of hyphae ceases, elongating and forks into two equal branches. More often branching is sub apical and lateral,, leaving the leading hyphal apex free to continue its growth. This type of branching may be:, dichotomous, verticillate, cymose and racemose. On the basis of presence or absence of septa, the hyphae of mycelical fungi are of two types (Fig.5.1):, (A) Nonseptate or aseptate hyphae – These are characteristic of oomycetes and, zygomycetes where the mycelium contains numerous nuclei lying in a common mass, of cytoplasm as in phycomycetes. Such a condition is known as coenocytic. There are, no cross walls in the hyphae. However, septa may be laid down at the time of, formation of reproductive organs to delimit them from the rest of the vegetative, hyphae. Pseudosepta are found in Allomyces., , Fig.5.1: Somatic Hyphae. A. Coenocytic (nonseptate hyphae) B. Septate Hyphae, , (B) Septate Hyphae – These are characteristic of Ascomycotina, Basidiomycotina, and, Deuteromycotina where the hyphae are septate and hyphal segments may contain one,, two or more nuclei. There are two types of septa:, a. Primary septa – Primary septa are formed in association with mitotic or meiotic, nuclear division, and they separate the daughter nuclei. These types of septa are found, in Ascomycotina, Basidiomycotina and their asexual states., b. Adventitious septa – Adventitious septa are formed in the absence of mitosis or, meiosis and occur especially in association with change in the local concentration of, UTTARAKHAND OPEN UNIVERSITY, , Page 110
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , cytoplasm. These are found in lower groups of fungi as mastigomycotina and, zygomycotina., , Structure of fungal cell - With the exception of slime moulds (Myxomycotina) the fungal, cell unusually consists of a strong, rigid cell wall enclosing the protoplasts., , Cell wall – The cell wall serves a number of important roles in fungi. It determines the, characteristic shape of a cell. The wall acts as an interface between the protoplasts and the, environment; it protects the cell from osmotic lysis and perhaps from the metabolites of other, organisms: it also acts as a binding site for some enzymes. The chemical composition of the, cell wall is not the same in all fungi. Cell wall composition appears to be an important, criterion of fungal relationships. Table 1.1 illustrates this tendency. Chitin is characteristically, present in the cell walls of most fungi. The chitin in fungal cell wall is not strictly identical, with animal chitin, and the formula (C22H54N4O21)n has been suggested for the fungal chitin:, It is a polymer of N-acetylglucosamine. Electron microscopic studies reveal that cellulose, and chitin occur as elongated microfibrillar units., , TABLE 1.1 Cell Wall Compositions in the Fungi, Cell Wall Category, , Taxonomic Group, , Representative Genera, , I., , Cellulose-Glycogen, , Acrasiomycetes, , Polysphondylium, Dictyostelium, , II., , Cellulose-β-Glucan, , Oomycetes, , Phytophthora, Pythium, , III., , Cellulose–Chitin, , Hyphochytridiomycetes, , Rhizidiomyces, , IV., , Chitin–Chitosan, , Zygomycets, , Mucor, Phycomyces, , V., , Chitin-β-Glucan, , Chytridiomycetes, , Allomyces, , Ascomycetes, , Neurospora, , Deuteromycetes, , Aspergilllus, , Basidiomycetes, , Fomes, Polyporus, , Ascomycetes, , Saccharomyces, Candida, , VI., , Mannan-β-Glucan, , Fungal Tissue, The fungal mycelium generally is a mass of hyphae interwoven loosely to form a network., During certain stages of the life history of most fungi the mycelium becomes organized into, loosely or compactly woven tissues, as distinguished from the loose hyphae ordinarily, composing a thallus. The term plectenchyma (a woven tissue) is used for all organized, tissue. Two general types of plectenchyma are recognized – Prosenchyma (approaching a, tissue) is a rather loosely woven tissue in which the component hyphae lie more or less, parallel to one another on their typically elongated cells are easily distinguishable as such,, Pseudoparenchyma (a type of plant tissue or false parenchyma) consists of closely packed,, more or less isodiametric or oval cells resembling the parenchyma cells of higher plants. In, this type of fungal tissue, the hyphae have lose their individuality and are not distinguishable, as such. (Fig.5.2), UTTARAKHAND OPEN UNIVERSITY, , Page 111
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Prosenchyma and Pseudoparenchyma compose various types of somatic and, reproductive structure. There are two such somatic structures the stroma (Pl. Stromata means, matters) and the sclerotium (Pl. Sclerotia means hard). A stroma is a compact, somatic, structure much like a mattress on which, or in which fructifications are usually formed. A, sclerotium is a hard resting body resistant of unfavourable conditions; it may remain dormant, for long periods of time and germinate on the return of favourable conditions., , (A) Prosenchyma, , (C), , (B) Pseudoparenchyma, , (D), , (E), , Fig.5. 2 Fungal Tissue A. Prosenchyma; B. Pseudoparenchyma; C. Stroma; D. Part of Stroma, E. Sclerotia in Rye grain, , Specialized somatic structures, Rhizoids – A rhizoid is a short, root like filamentous branch of the thallus, generally formed, in tufts at the base of the thallus. Rhizoids may be present in both, unicellular chytrids, (Rhizophydium) as well as mycelial (Rhizopus) thalli, Rhizoids function as anchoring and, absorbing structures., , Rhizomorphs – There are fungi whose hyphae aggregate together, behave as an organized, unit to form a root like strand in a thick, hard cortex and develop a growing tip somewhat, resembling that of a root tip. Such a structure is known as rhizomorph which mainly serves, the function of absorption. The rhizomorph can also survive unfavourable condition and its, growth may be renewed with the return of favourable condition., , UTTARAKHAND OPEN UNIVERSITY, , Page 112
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Appressoria (Sing. appressorium) – It is a terminal simple or lobed swollen, mucilaginous structure of germ tubes or infecting hyphae which adheres to the surface of the, host or other substratum and helps in the penetration of the infection hyphae. These are, formed by some parasitic fungi such as powdery mildews and rust., , Haustoria (Sing. haustorium) – A haustorium is an organ that is developed from a hypha, usually performing the function of absorption. They are characteristic of obligate parasites –, Uredinales, Erysiphales, and Peronosporales. They are intercellular sac-like, filamentous or, branched structure. They vary in shape and may be knob like or button shaped, elongated,, finger-like or branched. They secrete some specific enzymes which hydrolyse the protein and, carbohydrates of the host plant. (Fig.5.3)., , HAUSTORIUM, , Fig.5.3: A. Rhizoids; B. Rhizomorphs; C. Haustoria, , Hyphal traps (Snares) – The predacious fungi develop sticky hyphae or network of hyphal, loops known as hyphal traps or Snares. They help in capturing nematodes., , Stromata – These are compact somatic structures much like mattresses. Fructifications are, generally formed on or in them., , Mode of nutrition in fungi – Fungi are heterotrophic due to absence of chlorophyll., Hence, they are unable to synthesize carbohydrate food from inorganic materials and get it, readymade from other sources external to themselves. They are usually grouped as, saprophytes, parasites, obligate parasite, facultative parasite etc., It is probable that, when we learn more about the physiology of the fungi, we shall be able to, devise synthetic media to grow all the so-called obligate parasites. Fungi require already, elaborated food in order to live because, by lacking chlorophyll; they are incapable of, manufacturing their own food. But if given carbohydrates (glucose or maltose) in some form,, most fungi can synthesize their own proteins by utilizing inorganic or organic sources of, nitrogen and various mineral elements essential for their growth. (Fig.5.4), , Saprophytes – Those fungi which live on dead and decaying organic matter are known as, saprophytes. They luxuriantly grow on rotten fruits and vegetables, moist leather, bread,, jams, jellies, pickles, wood, dung etc. e.g., Mucor, Rhizopus, Aspergillus, Penicillium. Some, of these are incapable of growing on living organisms and survive only as saprobes. They are, known as obligate saprophytes. But there are some saprophytes which normally live as, UTTARAKHAND OPEN UNIVERSITY, , Page 113
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , saprophytes under favourable environmental conditions and on getting a suitable living, organism can parasitize it. Such fungi are known as hemisaprophytes or facultative parasites, e.g., Pythium debaryanum. Such fungi can easily be grown in an artificial medium., , Parasites – They obtain their food from living hosts. They are quite harmful and may cause, many serious diseases in the plants e.g., rusts, smuts, mildews, blights etc. Amongst these,, obligate parasites are those which can survive only in the presence of living host and they, cannot be cultured on an artificial medium e.g., Puccinia, Albugo, Peronospora. There are, some fungi which normally lead a parasitic life but under changed circumstances can live as a, saprophyte. They are known as hemiparasites or facultative saprophytes (e.g. Alternaria, spp.) and can also be grown on saprophytic substrates., Parasitic fungi obtain their nourishment from the host in various ways. Some parasitic fungi, live on the surface of the host and are known as ectoparasites (e.g. Erysiphe, Sphaerotheca)., A large number of fungi live inside hosts and are called as endoparasites (e.g., Synchytrium)., The mycelium of fungi like Albugo and Pythium may be intercellular of intracellular. In the, former case the mycelium is confined to the intercellular spaces of the host cells e.g., Albugo, spp. While in the latter it is found within the host cells e.g., Pythium spp. The parasitic fungi, produce haustoria for the absorption of food from the host cells. The haustoria may be small,, rounded, button-like as found in Albugo or much branched as in Peronospora., A special group of parasites is that of the predacious fungi which develop mechanisms for, capturing small animals such as eelworms (smaller nematodes lesser than 1/20th of an inch),, rotifers or protozoa. Predacious fungi use such animals as food. The hyphae produce a large, number of small loops which form a network and become sticky due to the presence of viscid, fluid. The eelworms which come in contact with such hyphae become motionless. A very, fine branch develops from the hyphae and penetrates into the body of the eelworm where it, swells and forms an infection bulb which gives rise to numerous branches completely filling, the body of the eelworm and absorbs food e.g. Arthrobotrys oligospora, Dactyllella, cionopaga. There are some fungi which parasitize their own kind and known as, mycoparasites e.g. Piptocephalis spp. Parasitizing Mucor and other related genera in the, order Mucorales., , Fig.5.4: Predaceous fungus, Arthrobotrys oligospora, , Symbionts - Fungi when live in close association with other organisms so as to be mutually, beneficial to each other are known as symbionts and the phenomenon is termed as symbiosis., UTTARAKHAND OPEN UNIVERSITY, , Page 114
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Some of the common examples of fungal symbiosis are lichens and mycorrhiza. The lichens, are formed by the symbiotic association of an alga and a fungus where the alga prepares food, and the encamping fungus by its spongy texture retains rain water which is supplied to the, alga along with mineral nutrients., Some fungi live in close association with the roots of higher plants particularly forest trees, and produce mycorrhiza which may be of two types: ectotrophic and endotrophic. In the, ectotrophic mycorrhiza the mycelium covers the entire surface of the root and may, sometimes penetrate it also. The mycorrhizal association increases the surface area of the root, system. Some of the fungi which form the ectotrophic mycorrhiza are: Amanita, Boletus,, Tricholoma and Russula. In host roots, they increase the nutrient uptake ability of the host., Such associations are commonly found within the members of the families Ericaceae and, Orchidaceae., Sometimes certain animals carry fungi (without being damaged by them) and give food and, shelter to them. This condition is described as commensalism., Saprophytic, parasitic fungi absorb their food through the hyphal cell walls, rhizoids and, haustoria. The hyphal walls are permeable while the plasma membrane is semipermeable., Many fungi secrete enzymes which dissolve the cell wall and hydrolyse the compounds, which become available to the fungus., , Reproduction, In fungi reproduction may take place by two methods; asexual and sexual. During both these, processes spores are the essential structures (in mycology the term spore is used for any, reproductive unit and is not necessarily the one after meiosis as in higher cryptogams). The, spores formed after meiosis are called meiospores and those resulting from mitosis,, mitospores. The ones falling under the category of meiospores are ascospores, basidiospores, and sporangiospores of slime moulds and under mitospores, zoospores, aplanospores,, conidia, uredospores are included under mitospores., The diploid body produced as a result of sexual fusion is known as zygote which in lower, fungi is termed as resting spore, oospore or zygospore. In higher fungi, the zygote is, represented by a diploid nucleus produced in a cell (ascus or basidium). This diploid nucleus, after undergoing meiosis results in the formation of haploid nuclei serving as centres for, haploid sexual spores called ascospores and basidiospores., , Asexual reproduction – It takes place by following means:(a) Fragmentation – The hyphae break into small fragments or pieces accidently or by, external force. Each piece upon getting suitable conditions, germinates to form a new, mycelium., , (b) Fission – This method involves the splitting of cells into two daughter cells by the, formation of a constriction followed by a cell wall formation. It is the most common method, of vegetative multiplication found in bacteria and yeasts (Fig.5.5)., , UTTARAKHAND OPEN UNIVERSITY, , Page 115
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.5.5: Asexual reproduction, A. Transverse cell division (fission) B. Budding, , (c)Budding – In this method, a small bud is formed from the parent cell which gradually, increases in size and receives a part of nucleus. A cell wall is formed which separates the, daughter cell from the parent cell. Each bud after separating from the parent cell develops, into a new individual. It is a common method of reproduction in yeasts(Fig.5)., (d)Sclerotia – These are perennating bodies formed by the compact masses of interwoven, hyphae. Sclerotia under suitable conditions germinate to form new individuals e.g. Claviceps,, Sclerotinia., , (e)Rhizomorphs – These are root-like elongated mycelial strands. They remain dormant, under unfavourable conditions and under favourable conditions develop into a new, mycelium., (All these above mentioned methods of reproduction are also known as methos of, vegetative reproduction)., Spores – These may be grouped in two categories: Endogenous and exogenous spores., Endogenous spores (Fig.5.6): These are formed within a sac-like spore producing structure, the sporangium which may be terminal or intercalary in position. Sporangia are produced on, sporophores which are known as sporangiophores. The sporangiophores may be branched or, unbranched. The entire contents or a part of the sporangium is converted into spores known, as sporangiospores. The spores may be motile or nonmotile. Motile spores are called, zoospores and the nonmotile aplanospores., , Fig.5.6 Asexual reproduction. A. Endogenous spores of Rhizopus B. Sporangium of Mucor, , UTTARAKHAND OPEN UNIVERSITY, , Page 116
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Zoospores (Gr. Zoon= animal + sporos =seed, spore) are commonly found in many lower, fungi e.g., Achlya, Saprolegnia, Pythium, Phytophthora, and Albugo. They are naked spores,, which after swarming, encyst, secrete a cell wall and germinate by germ tube into a thallus., They are equipped with one or two flagella (sing. Flagellum; L. Flagellum = whip). They are, of two types in fungi, the whiplash and tinsel. The whiplash flagellum as the name indicates, acts as a ‗whip‘ (commonly used by a horseman) has a rigid basal portion and a short upper, flexible region. The tinsel flagellum is a long hairy structure, consisting of a long rachis, having hair like structures on all sides. The flagella originate from a granule like structure, called blepharoplast, which lies deep in the rhizoplast (Gr. Rhiza=root+plastid). The, flagellum is composed of 11 parallel fibrils, nine peripheral forming a cylinder around two, central ones. Each fibril is composed of subfibrils. In a whiplash flagellum, the two central, fibrils are longer than peripheral, forming the whip and the bases of the fibrils are doubled up, within zoospore forming the blepharoplast. (Fig.5.7), , Fig.5.7: Zoospores, A. Posteriorly uniflagellate (whiplash); B. Anteriorly uniflagelate (tinsel);, C. Biflagellate zoospores having both whiplash and tinsel type., , On the basis of the flagellation, 4 types of zoospores are differentiated in fungi (1) posteriorly, uniflagellate zoospores (2) anteriorly uniflagellate zoospores (3) biflagellate zoospores, having tinsel and whiplash attached apically or laterally (4) biflagellate zoospores with two, whiplash on the anterior end.(Fig.5.8), , Fig.5.8: A- B. Zoosporangium containing zoospores in the process of liberation. C. Biflagellate, zoospores having tinsel and whiplash attached apically or laterally, UTTARAKHAND OPEN UNIVERSITY, , Page 117
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , The aplanospores are nonmotile and lack flagella and are formed inside the sporangium e.g., Mucor, Rhizopus. These spores may by uninucleate or multinucleate and possess two-layered, cell wall., , Exogenous spores, Conidia – All asexual spores, other than sporangiospores (zoospores and aplanospores) are, called conidia. They are produced externally on branched or unbranched hyphal tips termed, as conidiophores. The conidia may be formed singly or in chains. The conidial chains may be, basipetal or acropetal in succession. Conidia may be uninucleate or multinucleate. The latter, type is more common in the members of the form class Deuteromycetes. The shape, size and, colour of the conidia vary greatly and hence have been utilised in the identification of many, fungi., There are two main types of conidia (i) thallospores and (ii) conidiospores., Thallospores are formed by the transformation of existing cells of the thallus and are set free, when the parent hyphae decay. These are of two kinds (Fig.5.9):, (1) Arthrospores (oidia) – They are produced by fragmentation of hyphae from apex, to base. Each cell thus formed rounds off and separates as a spore which under, favourable circumstances germinates and forms the mycelium., (2) Chlamydospores – They are formed by rounding off and enlargement of terminal or, intercalary cells of a hypha. These can be single or formed in chains. They do not, separate from the hyphae but remain viable and germinate under favourable, conditions., , Fig.5.9: Asexual reproduction, A. Hypha fragmentation into oidia also called arthrospores; B., Chlamydospores, , The conidiospores or ‗true conidia‘ are formed as new elements from the thallus and on, maturity get cut off from the conidiophores. They can be of the following three types:, (1) Blastospores – They are formed as buds from the somatic cells of a hypha or, conidiophores., , UTTARAKHAND OPEN UNIVERSITY, , Page 118
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (2) Aleuriospores – These conidiospores are produced by the inflation of the apex of the, conidiophores and later this swollen apex gets cut off by a septum. They are generally, formed sympodially (Trichothecium, Arthrobotrys)., (3) Phialospores – The phialospores are conidia which get cut off from flask-shaped,, cylindrical phialides. They are generally cells of limited growth, , Sexual reproduction, It involves the fusion of two compatible nuclei. Three distinct phases have been recognised, on the basis of nuclear behaviour:, Phase 1. Plasmogamy – It is union of protoplasts which brings together two sexually, compatible nuclei in a single cell. This process is known as plasmogamy., Phase 2. Karyogamy – Fusion of the two compatible nuclei resulting in the formation of a, diploid nucleus is known as karyogamy. In majority of the species, plasmogamy is followed, by karyogamy but in higher fungi, the fusion is delayed and nuclei lie close to each other, without fusion. Such a pair of nuclei is known as dikaryon and the phase termed as dikaryotic, phase., , Phase 3. Meiosis – After the nuclear fusion a division takes place which reduces the, chromosome number to half. The gametes taking part in the sexual fusion may be, morphologically or physiologically different and they are termed as plus (+) and minus (-), strains. When both male and female sex organs occur on the same mycelium, the fungus is, known as monoecious or homothallic and when they occur on different mycelia, the fungus, is said to be dioecious or heterothallic., In the formation of sex organs either entire thallus (holocarpic) or only a part of thallus, (eucarpic) is involved. The sex organs of fungi are called gametangia (sing. gametangium), and sex cells produced by them are known as gametes. When the gametangia and gametes are, morphologically indistinguishable they are known as isogametangia and isogametes, respectively. When male and female gametangia and gametes are morphologically different,, they are known as heterogametangia and heterogametes respectively. In heterogametangium, the male gametangium is called antheridium and the female as oogonium. Antheridium, produces male gametes which are known as antherozoids or sperms and the female forms an, egg or oosphere., , Plasmogamy – There are many ways by which the two compatible nuclei are brought, together and any of the following methods can be involved in the process:, 1. Planogametic copulation – In this type of copulation, two naked gametes fuse and, if the gametes are motile, they are known as planogametes. In Synchytrium the fusing, gametes are isogamous while in Allomyces spp. they are anisogamous. On careful, biochemical and genetical analyses, it has been found that even the isogametes are, physiologically and chemically different from each other. In Monoblepharis,, however, heterogamous planogametic conjugation is found where it has been seen, that the male gamete (antherozoid) is motile and the female (oosphere) non-motile, and borne in a female gametangium, the oogonium.(Fig.5.10), , UTTARAKHAND OPEN UNIVERSITY, , Page 119
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.5.10 Sexual reproduction, A. Isogametes; B. Anisogametes; C. Heterogametes, , 2. Gametangial contact – Another method by which plasmogamy is brought about is, the contact of male and female gametangia where both the gametes (male and female), , Fig.5.11 Sexual reproduction, Plasmogamy through gametangial contact in Pythium spp., , are non-motile. The nuclei of the male gametangium (the male gamete consists of nuclear, material) are transferred into the female when the two gametangia of opposite sex come, in close contact with each other. The nuclei from male gametangium migrate to the, female one through a pore formed at the point of contact of two gametangia, (Sphaerotheca spp.) or through a short fertilization tube formed during the process, (Phytophthora spp.). In the latter case, after the migration of the nuclei, antheridium, generally degenerates and the oogonium develops further. Sometimes as in the case of, Pyronema sp. the contact takes place through a short or a long tubular enlargement the, trichogyne formed by the female gametangium. (Fig.5.11), , UTTARAKHAND OPEN UNIVERSITY, , Page 120
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Gametangial copulation is very common amongst lower fungi. Here the process involves, the fertilization of oosphere or oospores found within the female gametangium known as, oogonium. The process here is referred to as oogamy (in all Oomycetes)., 3. Gametangial copulation – In this method, the two gametangia fuse entirely. This, may take place by two ways, in the first method, the contents of the one gametangium, pass into the other through a pore formed in the gametangial wall at the point of, contact. In the second method, the two gametangial cells fuse by the dissolution of the, wall which after fusion form a single cell as seen in Mucorales and Entomophthorales, (higher members of lower fungi) while is some Chytrids (lower fungi) the contents of, the smaller (male) gametangium pass into the larger (female) gametangium(Fig.5.12)., , Fig.5.12 Sexual reproduction, Plasmogamy through gamentangial copulation, , 4. Spermatization – Some higher fungi (Ascomycetes adn Basidiomycetes) produce, small uninucleate male structures known as spermatia (sing. spermatium). These are, disseminated by insects, wind, water or by other agencies to a specialised hyphae, the, receptive hyphae which behave as a reduced female gametangia. A pore develops at, the point of contact and the nuclei (male) migrate from the spermatium to the, receptive hyphae resulting in a binucleate (dikaryotic) cell (Fig.5.13)., , UTTARAKHAND OPEN UNIVERSITY, , Page 121
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.5.13 Sexual reproduction, Plasmogamy by means of spermatization, , 5. Somatogamy – In many fungi, no normal sex organs are formed and vegetative cells, behave as functional gametangia. This process is absent in lower fungi but very, common in the members of Ascomycetes and Basidiomycetes., , (i) Karyogamy – This generally occurs immediately after plasmogamy in lower fungi, where fusion between two nuclei of opposite sex takes place. This process, however, is, delayed in higher fungi where the result of plasmogamy is a dikaryotic cell (the two nuclei of, opposite sex lying unfused). Sometimes the dikaryon cell may divide into more dikaryons, and each time nuclei replicating the original pair. Sometimes the hyphae having dikaryotic, cells form a definite tissue developing into a special layer, the hymenium. These dikaryotic, cells after karyogamy develop into specialised cells asci in Ascomycetes and basidia in, Basidiomycetes., , (ii) Meiosis – Karyogamy is followed by a reduction division which is the last important, process in the reproduction. During meiosis of the diploid nucleus the chromosomes do not, split but separate out as a whole into two complete sets. Each of the sets forms the, chromosome complement of a haploid daughter nucleus. In this process some of the, chromosomes in each daughter nucleus are derived from one parent and others from the other, parent. Subsequently, mitotic divisions take place resulting in and increase in the number of, haploid nuclei within the zygote cell. In the case of planogametes undergoing isogamy or, anisogamy the resulting zygote is a resting sporangium. This resting sporangium produces, zoospores which encyst individually and germinate giving rise to a germ tube. In cases where, the resultant zygote is an oospore, it germinates directly giving rise to a germ tube(s), (Phytophthora spp.) or it indirectly results in a resting sporangium where in zoospores are, produced (Albugo spp.). In other cases where a zygospore is formed, it germinates producing, a short germ tube with an apical sporangium known as germ sporangium containing, aplanospores (Mucor spp.)., , UTTARAKHAND OPEN UNIVERSITY, , Page 122
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Nuclear cycle, As in higher plants, generally there is a cycle of haploid and diploid structures, equivalent to, gametophyte and sporophyte generations. However, like higher plants there may not be, distinct alternation of generations. In majority of fungi, the diploid phase starts after fusion of, nuclei (Karyogamy) and may occupy a very small portion of the life cycle as compared to, predominantly haploid phase. They are extremely small making their study very difficult., Electron microscopy has revealed that somatic nuclei divide in a manner not directly, comparable to mitosis in that no spindles or metaphase plates are formed. The meiotic, divisions in fungi are typical are comparable to those of more advanced members. (Fig.5.14), , Fig.5.14 A generalised life cycle, , 5.4 CLASSIFICATION OF FUNGI, Although fungi are placed in the plant kingdom because of similarty in the structure of their, thalli and in their reproduction by spores, mycologists now believe that most fungi have, originated from some ancestral protozoan like flagellates. Ainsworth treated fungi either as a, separate kingdom or as a sub-kingdom belonging to plant kingdom, with two divisions; the, Myxomycota for plasmodial forms; and the Eumycota, for non-plasmodial forms which are, frequently mycelial. Eumycota was further divided into five subdivisions, including the, Ascomycotina (for ascomycetes) and the Basidiomycotina (for basidiomycetes). For, convenience, the imperfect fungi were classified as the Deuteromycotina, although in a, hierarchial classification it is incorrect to equate these fungi with the asomycetes and, UTTARAKHAND OPEN UNIVERSITY, , Page 123
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , i. Class – Myxomycetes, These are commonly called the true or plasmodial slime molds and are sometimes, also reffered to as acellular slime molds. The trophic phase in these fungi is a free-living,, mobile, acellular (coenocytic) multinucleate, saprobic plasmodium. The spores develop in, masses with a persistent peridium inside a fructification. On germination, each spores, liberates one to four flagellated swarm cells. Asexual reproduction occurs by binary fission., Sexual reproduction takes place by fusion forming zygote that develop into plasmodia., , ii. Class – Plasmodiophoromycetes, These are commonly known as the endoparasitic slime molds, consists of a naked, holocarpic plasmodial thallus with plasmodial movement and feeding. Members are obligate, parasites of algae, aquatic fungi and higher plants. The somatic phase is plasmodium which, develops inside the host cells. The zoospores are bilflagellate with two anteriorly inserted, whiplash flagella of unequal size. These zoospores possibly fuse (but remain binucleate), before infecting the host, to form a cystogenous plasmodium, whicch gives reise to thick, walled cysts (resing spores). Cyst formation is probably preceded by karyogamy and, followed by meiosis., , II., , Division – Eumycota, a. Subdivision – Mastigomycotina, i. Class - Chytridiomycetes, , The motile cells of these fungi have a single posterior whiplash flagellum. The, flagellum is attached to a structure termed blepharoplast within the cell. Sexual reproduction, takes place usually by the fusion of motile isogamous gametes or anisogametes; or by the, fusion of a nonmotile femate gamete with a otile male gamete; or by the fusion of, rhizomycelia ; or by the conjugation of a small and a large thalli , resulting in the formation, of a thick walled resting body., , ii. Class – Oomycetes, These are typically aquatic, either free-living or parasitic on algae, water molds, small, animals and other forms of aquatic life, although some are terrestrial. The Oomycetes are, characterized by:, 1. Production of biflagellate zoospores with two types of flagella; the shorter flagellum, of the tinsel type directed forward; and the whiplash type directed backwards. The, flagella may be anteriorly or laterally inserted on the zoospores; two types of, zoospores formed in some species; one pear-shaped and the other reniform;, 2. An advanced type of oogamous reproduction takes place ;, 3. Meiosis is gamentangial rather than zygotic, and the vegetative thallus is diploid;, 4. The life cycle is of the haplobiontic type., , b. Subdivision – Zygomycotina, i. Class – Zygomycetes, UTTARAKHAND OPEN UNIVERSITY, , Page 127
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , This class is represented by the presence of coenocytic hyphae, absence of motile cells, and sexual reproduction that occurs by gametangial copulation and results in the formation of, a zygospores. Asexual reproduction occurs typically by non-motile sporangiospores., , c. Subdivision – Ascomycotina, i. Class – Hemiascomycetes, (hemi = half + part) The class is characterized by the absence of an ascocarp so that, the asci are naked and lack sterile cells. The wall of the asci are generally thin and release the, ascospores by bursting. Cells may often remain attached to each other for varying periods of, time. These are most primitive among Ascomycotina., , ii. Class – Plectomycetes, These are characterized by the globose evanescent asci arising at different levels from, the ascogenous hyphae in a closed fruiting body, the cleistothecium. The asci are typically 8spored. The wall of the cleistothecium varies from loosely woven to distinct peridium that, may be one- to several layers thick. The majority of members are saprobic. However, a few, are parasitic on plants, and few on animals, including man. The fungi beloging to this class, are of great economic importance., , iii. Class – Pyrenomycetes, These are defined as ascomycetes with ascocarps entirely surrounded by a peridial, wall and containing unitunicate asci which are primarily arranged in a hymenial layer. The, ascocarps are provided with an opening, the ostiole. The members grow on wide range of, habitats. Some are important plant pathogens, while others are fungal symbionts of lichens., , iv. Class – Discomycetes, These ascomycetous fungi produce fructifications with an exposed hymenium, called, apothecia (sing. apothecium; Gr. apotheke = store house). Most of these are cup-shaped or, even mushroom – shaped. All the Discomycetes eject their spores forcibly except the, Tuberales., , d. Subdivision – Basidiomycotina, i. Class – Teliomycetes, This class includes two important gorups of plant pathogens, the rusts and the smuts., The characteristic feature is the production of a thick-walled resting spore, the teliospore in, which karyogamy takes place. In teliomycetes a simple pore similar to those of the, Ascomycotina and the characteristic septum found in other Basidiomycetes, the dolipore, septum, is absent., ii. Class – Hymenomycetes, This is the largest class of the subdivision Basidiomycotina. It includes the fungi, popularly called toadstools, bracket fungi, polypores, mushrooms, fairy clubs, jelly fungi,, coral fungi. The characteristic features are the formation of basidia in a hymenium,, UTTARAKHAND OPEN UNIVERSITY, , Page 128
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , gymnocarpous or semiangiocarpous nature of the basidiocarp and the explosive discharge of, the basidiospores., , e. Subdivision – Deuteromycotina, i. Class – Hyphomycetes, In these imperfect fungi conidia are formed from aggregated or separated modified, hyphae borne on the exterior face of substrates and enclosed by additional fungal or host, tissue., , ii. Class – Coelomycetes, These are imperfect fungi in which conidia ae formed within a cavity lined by either, fungal tissue, host tissue, or a combination of both. These are mainly the asexual states of, Ascomycotina, however, the possibility that some may yet be correlated with the, Basidiomycotina cannot be excluded., , 5.6 ECONOMIC IMPORTANCE OF FUNGI, The fungi are of great economic importance on account of their both harmful as well as, beneficial effects. A large number of fungi cause destructive havoc to our valuable crop and, timber plants, various types of food products. They also attack the live-stock as well as, human beings. But, all of them are not harmful to the mankind, as most of the species bring, about decomposition of dead bodies of plants and animals as well as of animal dung. In, addition they are also useful in the production of new age medicines and other useful, products., There are several species of fungi which are of tremendous economic importance. They are, beneficial as well as harmful to man., (a) Beneficial activities of fungi, (i) Edible Fungi – Fungi provide us food that is rich in proteins. Dried yeasts contain about, 50 per cent protein. Besides, they are rich in vitamin and B-complex. Mushrooms are, generally members of Basidiomycetes. Fruiting bodies of about 105 saprophytic mushrooms, are edible; they are preferred for both their taste and food value. Most of the edible fungi are, the members of Basidioycetes and Ascomycetes, for example:, Edible fungi of Ascomycetes, , Saddle fungi – Helvella and Gyromitra, , , , Morels – Morchella and Verpa, , , , Truffles – Species of Tuber and Cyttaria, , Edible fungi of Basidiomycetes , , Jew‘s ear fungi – Hirneola auriculajudae adn Hirneola polytricha, , , , Mushrooms – Species of Agaricus, , UTTARAKHAND OPEN UNIVERSITY, , Page 129
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , Pore fungi – Boletus, Strobilomyces and Fistulina, , , , Teeth fungi – Species of Hydnum, , , , Giant puffball – Clavatia mexima and Lycoperdon species, , BSCBO-101, , (ii) Role of Fungi in Agriculture:, Fungi and nitrogen fixation – Some soil fungi are beneficial to agriculture because, a, small amount of atmosphere nitrogen is also fixed by non-symbiotic fungi such as, Rhodotorula and Saccharomyces., , Soil fertility – Some soil fungi maintain the fertility of soil. The saprophytic fungi, particularly in acid soils where bacterial activity is at its minimum cause decay and, decomposition of dead bodies of plants and their wastes taking up the complex organic, compounds (cellulose and lignin) by secreting enzymes. The enzymes convert the fatty,, carbohydrate and nitrogenous constituents into simpler compounds such as carbon dioxide,, water, ammonia, hydrogen sulphide etc. Some of these return to the soil to form humus and, rest to the air from where they can again be used as raw material for food synthesis. Some, fungi like Aspergillus, Cladosporium, Rhizopus, Penicillium, etc. have soil binding property., This is achieved by the secretion of mucilaginous substances. Some common fungal, inhabitants of the soil help to combat diseases caused by soil borne fungi. Trichoderma, lignorum and Gliocladium fimbriatum are found in damp soils. They have an inhibitory effect, on the growth of the mycelium of Pythium. They serve to suppress fungi causing the damping, off disease of seedlings and thereby influence favourable the growth of crops. There are some, predacious fungi in the soil. They trap and destroy the nematodes., , (iii) Role of Fungi in Industry:, Baking industry – Saccharomyces cerevisiae (yeast) popularly known as baker‘s yeast is, widely used in baking industry. Alcoholic fermentation is the basis of baking industry,, because the fermentation of sugar solutions by yeasts produces ethyl alcohol and carbon, dioxide. Carbon dioxide is collected, solidified and sold as dry ice. In the baking industry, CO2 is the useful product. It serves two purposes: (i) causes the dough to rise, (ii) makes the, bread light., , Production of alcoholic beverages – The other by product of fermentation of sugar or, malt solution is alcohol. The enzyme zymase present in yeast cells convert hexose sugars into, alcohol., , Acid production – Several fungi are helpful in the commercial production of many organic, acids, for example, Aspergillus niger in citric and oxalic acid, A. Gallomyces in gallic acid,, Penicillium purpurogenum in gluconic acid, Mucor in fumeric acid, Rhizopus oryzae in lactic, acid., , Enzyme production – Many fungi produce enzymes which have industrial uses, for, example, amylase from Aspergillus, invertase from Alternaria and Saccharomyces, and, zymase from Saccharomyces., , UTTARAKHAND OPEN UNIVERSITY, , Page 130
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Cheese making – Penicillium camemberti adn P. Roquefortie are used in cheese making., These moulds add a special flavour to the cheese., , Vitamin extraction – the yeasts are the best sources of vitamin B complex, Vit. B12 is, extracted from Eremothecium ashbyji and Vit. A from Rhodotorula gracilis., , Source of hormones – Gibberellins are plant hormones produced by the fungus Gibberella, fujikoroi which causes a disease of rice accompanied by abnormal elongation. Gibberellin is, used to accelerate growth of several horticultural crops., , (iv) Role of fungi in medicine – At present there are more than 700 fungal species which, secrete antifungal and antibacterial substances. These substances are called antibiotics. The, first antibiotic penicillin was extracted from Penicilliium notatum by Sir Alexander, Flemming, for which he was awarded Nobel Prize in 1945. Some important antibiotics and, their sources are as follows:, Antibiotics, , Fungal source, , I, , Streptomycin Streptomyces griseus, , II, , Penicillin, , Penicillium notatum and P. Chrysogenum, , III, , Ramycin, , Mucor rammannianus, , IV, , Brefelidin, , Penicillium brefedianum, , V, , Fumigallin, , Aspergillus fumigates, , VI, , Clavacin, , Calvaria, , VI, , Griseofulvin, , Penicillium griseofulvum, , VII Ergotin, , Claviceps purpurea, , Some of the cholesterol and blood pressure lowering drugs are also obtained from certain, fungi, e.g. mevastatin from penicillium citrinum and lovastatin from monnascus ruber., , (v) Fungi in Biological Research – Use of microorganisms in determining the potency of, drugs, detection and estimation of various chemicals in given samples is known as the, biological assay. Amongst fungi, Aspergillus niger is used to detect very minute quantities of, Zn, Ca, Pb, Mn, Cu, etc. in given samples. Neurospora is an ideal material for genetic and, biochemical studies. It is popularly known as ‗Drosophila of Plant Kingdom‘, because of its, suitability in the studies of biological sciences., , (b) Harmful activities of fungi, (i) Plant diseases – Fungi have a negative value because they are the causative agents of, different diseases of our crop, fruit and other economic plants. These fungal diseases take a, heavy toll and cause tremendous economic losses. Some important plant diseases and their, causative agents are given in table., , UTTARAKHAND OPEN UNIVERSITY, , Page 131
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Table:1- Some Important Plant Diseases, Name of disease, , Fungus, , 1., , Early blight of potato, , Alternaria solani, , 2., , Late blight of potato, , Phytophthora infestans, , 3., , Loose smut of oat, , Ustilago avenae, , 4., , Brown leaf spot of rice, , Helminthosporium oryzae, , 5., , Black or stem rust of wheat Puccinia graminis tritici, , 6., , Loose smut of wheat, , Ustilago nuda tritici, , 7., , Powdery mildew of wheat, , Erysiphe graminicola, , 8., , Ergot of bajara, , Claviceps microcephala, , 9., , Loose smut of barley, , Ustilago nuda hordei, , 10. White rust of crucifers, , Albugo candida, , 11. Green ear disease of bajara, , Sclerospora graminicola, , 12. Tikka disease of groundnut, , Cercospora arachidicola, , (ii) Deterioration of food and other articles – Saprophytic fungi for example Rhizopus,, Mucor, Aspergillus grow on food articles such as bread, jam, pickles, and make them, inedible. They also destroy leather articles. Tubber, wool and painted surfaces are also get, damaged by species of Aspergillus, Penicillium, Alternaria and Rhizopus., (iii) Decay of wood – In India the commercial timber yielding plants such as sal, teak, sisam, are destroyed by Polyporus, Ganoderma etc. These fungi secrete cellulose and lignin, decomposing enzymes and cause ‗heart rot‘., (iv)Fungal toxins – Mushrooms like Amanita phalloides, A. Virosa are poisonous., Poisoning of these mushrooms causes abdominal pains with vomiting, sweats, diarrhoea etc., Claviceps purpurea, a parasitic fungus contains a powerful poison and causes gangrenes., LSD (Lysergic acid diethylamide), a hallucinogenic and hypnotic compound, is also obtained, from Claviceps. Besides this, some fungi secrete a group of toxic/carcinogenic compound, called aflatoxins., (v) Human and animal diseases – Some species of Aspergillus such as A. fumigates, A., flavus and A. niger are human pathogens. They cause disease collectively known as, aspergilloses. The symptoms of this disease are similar to tuberculosis. Many parasitic fungus, Imperfecti live in the mucous membranes of throat, bronchi and lungs and cause infection of, mouth and lungs. A few fungi cause serious diseases of domestic animals. Some fungal, disease of humans are given in table., , UTTARAKHAND OPEN UNIVERSITY, , Page 132
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Table :2- Some Fungal Diseases of Humans, Disease, , Pathogen, , 1. Ringworm, , Microsporon ianosum, , 2. Dobhi-itch, , Epidermophyton floceosum, , 3. Candidiasis, , Candida albicans, , 4. Athelete foot, , Trichophyton interdigitate, , 5. Blastomycosis Blastomyces dertimidis, 6. Aspergilliosis, , Aspergillus flavus, A. Fumigates, A. Niger, , 7. Penicillosis, , Penicillium sp., , 5.7 SUMMARY, This chapter has highlighted the physiological biodiversity of fungi in terms of morphology,, growth, metabolism and cell reproduction. Understanding the diverse vegetative as well as, reproductive structure produced by different fungi and the ways in which fungi interact with, their growth environment is crucial for the identification and their management for human, welfare., While classification is very important for systematic study of any organism, there are, different views/criteria used by different scientists in classifying fungi. This leads to many, useful ways of grouping them, with the groups created by one definition of similarity, different to those created by another. Stable or ideal system for fungal classification is yet to, be proposed although several systems of classificcation have been proposed from time to, timy by taxonomists. In this unit, general key characteristics at class level is given to look at, some aspects of fungal classification and identification so as to get an idea of how, mycologists have gone about studying fungi over the past two century., Fungi have been utilized for thousands of years for the production of various foods and, beverages. While these applications are still important, fungi are now being used in novel, ways for the production of antibiotics and enzymes. It is very obvious that fungi are, economically very important and continued use of fungi on large scale by humans is, guaranteed., , 5.8 GLOSSARY, Acervulus (pl. Acervuli) - a mat of hyphae giving rise to short conidiophores closely packed, together forming a bed-like mass., Acropetal - refers to spore formation where the most recently formed spore is at the tip of a, chain of spores. Usually seen as being smaller than the immediate neighbour. Note that a, continuous cytoplasmic link exists from base to tip., Acervulus (pl. Acervuli) - a mat of hyphae giving rise to short conidiophores closely packed, together forming a bed-like mass., UTTARAKHAND OPEN UNIVERSITY, , Page 133
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Apical - at the apex or end., Apothecium - cup shaped ascocarp. Hymenium is exposed at maturity., Appressorium - a swelling on a germ tube or hyphae, often terminal, which may attach to, the surface, especially in development of colonisation of a cell., Ascocarp - a fruiting body containing one or more asci., Ascomycota - one of the four divisions within the Fungal Kingdom. Contains three classes,, Laboulbeniomycetes, Protoascomycetes, Euascomycetes. Characterised by the formation of, ascospores., Ascospore - a sexual spore formed following meiosis in an ascus., Ascus (asci) - a sac-like cell generally containing a definite number of ascospores, typically, 8, formed after karyogamy and meiosis., Asexual - mitotic reproduction, not involving fusion of nuclei and meiosis, offspring the, same as the single parent., Basidiocarp - a fruiting body that bears basidia., Basidiospore - a sexual spore formed following meiosis, borne on a basidium., Basidium (basidia) - a structure bearing on its surface a definite number of basidiospores, (usually four) that are formed following karyogamy and meiosis., Chitin - principle microfibrillar component of cell walls of fungi, composed of (1 - 4 ) linked, polymer of N-acetyl-glucosamine., Clamp connection - a bridge-like hyphal connection between two adjacent cells, found only, in some Basidiomycota., Class - fungal divisions are divided into classes. Classes are divided into orders., Columella (pl. columellae) - a sterile extension of the stalk into the sporangium of some, zygomycetes., Conidiophore - a simple or branched hyphae arising from somatic hyphae which bears at its, tip or sides, cells which form or become conidia., Conidium (pl. conidia or conidiospore) - a nonmotile asexual spore formed on a, conidiophore, formed from or as an extension of the hyphal walls. May be single or, multicelled, simple or complex, round, elongated or spiral in shape. Found only in the, Ascomycota or Basidiomycota., Dikaryon - a hypha or portion of hyphae which contains two haploid nuclei in each cell., Dolipore - a central pore in a septum surrounded by a barrel shaped swelling of the septal, wall. Common in the Basidiomycetes., Ectomycorrhiza - type of mycorrhiza in which fungal hyphae grow around the root and, between cells of the epidermis., Endophyte - general term to describe a fungus which lives within healthy plant tissue. May, specifically refer to Balansioid fungi colonising grass leaves., Flagellum (pl. flagella) - fine long thread projecting from a cell having a lashing or, undulating motion which enables the cell to move when in water. Two types discussed in the, fungi, true fungi may have a whiplash flagellum and organisms now placed in the Chromista, may have whiplash or tinsel flagella., Haustorium - a specialised hyphal invagination of plant cells., Heterokaryotic - a mycelium which contains genetically different mating types., , UTTARAKHAND OPEN UNIVERSITY, , Page 134
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Heterothallic - a fungus which requires two different mating types to form sexual fruiting, bodies., Holdfast - projection from the thallus which attaches the thallus to a surface, may be called, an appressorium in the higher fungi., Holocarpic - all the thallus is used for the fruit body., Hyaline – colourless., Imperfect stage - the asexual stage of a life cycle., Karyogamy - fusion of two nuclei., Mycelium - mass of hyphae constituting the body of the thallus or fungus., Mycorrhiza - mutually beneficial association between plant root and fungus., Perithecium - a closed ascocarp with a true wall and an ostiolate opening., Pycnidium - an asexual fruiting body that is hollow, and partially lined inside, with conidiophores., Rhizomorph - a thick strand of organised hyphae resembling a fine root., Saprophyte - organism which obtains its organic nutrients in solution from dead or dying, tissues of any other organism., Sclerotium (sclerotia) - a hard, aggregation of hyphae which functions as a resting body. In, extreme cases, the body is surrounded by melanised hyphae forming a skin, in other cases,, the body tends to be diffuse., Sporangiolum (Sporangiola) - small sporangium containing a few sporangiospores., Sterigma - pointed projection on the outer surface of basidia from which basidiospores, emerge and are dispersed., Stroma (pl. stromata) - a compact, matress like somatic structure in or on which, reproductive structures form., Zoospore - motile naked spore formed within a sporangium., Zygospore - sexual spore resulting from the conjugation of gametes, found within a, zygosporangium, contains a diploid nucleus., Zygote - cell in which two nuclei of opposite mating type have fused., , 5.9 SELF ASSESSMENT QUESTIONS, 5.9.1 Multiple choice Questions:, 1. Columella is a specialized structure found in the sporangium of:, (i) Ulothrix, `, (ii) Spirogyra, (iii) Rhizopus, (iv) none of these., 2. A lichen can be described as a mutualistic relationship between an ascomycete and, a(n):, (i) angiosperm root, (ii) chytrid, (iii) archeabacterium, (iv) green alga, 3. Mycorrhiza exhibits the phenomenon of:, UTTARAKHAND OPEN UNIVERSITY, , Page 135
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , (i) symbiosis, (iii) antagonism, , BSCBO-101, , (ii) Parasitism, (iv) endemism, , 4. The black rust of wheat is a fungal disease caused by:, (i) Albugo Candida, (ii) Puccinia graminis tritici, (iii) Melampsora lini, (iv) Claviceps purpurea, 5. A mycelium is:, (i) a mutualistic relationship between a fungus and a plant., (ii) a mass of connected fungal hyphae., (iii) a partition between the cells of fungal hyphae., (iv) a specialized reproductive structure of a fungus, 6. Which of the following is not a characteristic of the fungi?, (i) Mitosis takes place within the nuclear membrane, (ii) They have cell walls made of chitin., (iii) They are all absorptive heterotrophs., (iv) They are all motile, 7. Absorptive heterotrophic nutrition is exhibited by:, (i) bryophytes, (ii) fungi, (iii) pteridophytes, (iv) Algae, , 8. Mycorrhiza is correctly described as:, (i) symbiosis of algae and fungi, (ii) symbiotic relationship between fungi and roots of some higher plants, (iii) parasitic association between roots and some fungi, (iv) relation of ants with the stem of some trees., 9. Puccinia forms uredia and:, (i) telia on wheat leaves, (iii) aecia on barberry leaves, , (ii) pycnia on barberry leaves, (iv) aecia on wheat leaves., , 10. An ascomycete can be distinguished from other fungi:, (i) by the presence of gills on the mycelium., (ii) by the presence of eight sexual spores in an ascus., (iii) because ascomycetes lack a dikaryotic phase., (iv) because ascomycetes are mainly diploid., 11. A basidium is typically observed in the common:, (i) bread mold, (ii) gilled mushroom., (iii) lichen, (iv) chytrid, , UTTARAKHAND OPEN UNIVERSITY, , Page 136
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 12. A wildlife pathologist is examining some skin tissue from a dead frog. She observes, the presence of a fungus. She cultures some of the fungal cells and notices that some of, the cells are flagellated. She concludes that the frog has a fungal disease caused by:, (i) a zygomycete, (ii) a basdiomycete, (iii) an ascomycete, (iv) a chytrid, 13. How many species of fungi are thought to exist?, (i) 1.5 billion, (ii) 150,000, (iii) 1500, (iv) 1.5 million, 14. Organisms which are indicator of SO2 pollution of air:, (i) mosses, (ii) mushrooms, (iii) lichens, (iv) puffballs, 15. Most of the lichens consist of:, (i) brown algae and higher plant, (iii) green algae and ascomycetes, , (ii) blue green algae and basidiomycetes, (iv) red algae and ascomycetes, , 16. Lichens indicate SO2 pollution because they:, (i) grow faster than others, (ii) are sensitive to SO2, (iii) show association between algae and fungi, (iv) flourish in SO2 rich environment, 17. Black rust of wheat is caused by:, (i) Ustilago, (iii) Albugo, , (ii) Puccinia, (iv) Phytophthora, , 18. You are walking in the woods and see a fungus that is unfamiliar to you. You, remove a reproductive structure, and take it home to examine further. When you look, at it under the microscope, you find a zygosporangium. Based on this information alone,, this fungus is an:, (i) zygomycete, (ii) chytrid, (iii) ascomycete, (iv) basidiomycete, 19. Which one of the following statement about lichens is wrong?, (i) these grow very rapidly (2 cm per day), (ii) some of its species are eaten by reindeers, (iii) they show fungal and algal symbiotic relationships, (iv) these are pollution indicators, 20. Adhesive pad of fungi penetrate the host with the help of:, (i) mechanical pressure and enzymes, (ii) hooks and suckers, (iii) only by mechanical pressure, (iv) softening by enzymes, UTTARAKHAND OPEN UNIVERSITY, , Page 137
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 21. Which pair of the following belongs to basidiomycetes?, (i) Peziza and stink horns, (ii) Puffballs and Claviceps, (iii) Morchella and mushrooms, (iv) Birds nest fungi and puffballs, 22. In Fungi food materials are digested:, (i) within food vacuole, (ii) Outside the body, (iii) By Lysosomes, (iv) By Mitochondria, 23. Fungi penetrate their host by:, (i) Mechanical means, (iii) Mechanical and enzymatic action, , (ii) Enzymatic action, (iv) By hook and suckers, , 24. In Penicillium, the hyphae are:, (i) Septate and coenocytic, (iii) Septate and multiinucleate, , (ii) Septate and uninucleate, (iv) None of these, , 25. The walls of fungi are composed of:, (i) Starch, (ii) Cuttin, (iii) Cellulose, (iv) Chitin, 26. Fungi that use in baking industry respire?, (i) Aerobically, (ii) Anaerobically, (iii) Both (i) and (ii), (iv) None of these, 27. Which fungal disease spreads by seed and flowers?, (i) soft rot of potato, (ii) covered smut of barley, (iii) loose smut of wheat, (iv) corn smut, 28. Coenocytic hyphae are:, (i) Septate with heavy cytoplasm, (ii) Uninucleated with common cytoplasm, (iii) Multinucleated with separated cytoplasm, (iv) Aseptate, multinucleate with common cytoplasm, 29. Which of the following secretes toxins during storage conditions of crop plants?, (i) Colletotrichum, (ii) Aspergillus, (iii) Albugo, (iv) All of these, 30. A loosly woven fungal tissue is called:, (i) Prosenchyma, (ii) Pseudoparenchyma, (iii) Stroma, (iv) Plectenchyma, , 5.9.1 Answers key:, UTTARAKHAND OPEN UNIVERSITY, , Page 138
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 01., , (iii), , 07., , (ii), , 13., , (iv), , 19., , (i), , 25., , (iv), , 02., , (iv), , 08., , (ii), , 14., , (iii), , 20., , (i), , 26., , (ii), , 03., , (i), , 09., , (i), , 15., , (iii), , 21., , (iv), , 27., , (iii), , 04., , (ii), , 10., , (ii), , 16., , (ii), , 22., , (ii), , 28., , (iv), , 05., , (ii), , 11., , (ii), , 17., , (ii), , 23., , (iii), , 29., , (ii), , 06., , (iv), , 12., , (iv), , 18., , (i), , 24., , (ii), , 30., , (i), , 5.10 REFERENCES, , , Ainsworth & Bisby's Dictionary of the Fungi (10th Ed), 2008 CAB International,, Wallingford, UK., , , , Benjamin DR 1995 Mushrooms, Poisons and Panaceas, WH Freeman and Co, New York., , , , Carlile MJ & Watkinson SC 2000, The Fungi, Academic Press, London., , , , Dighton J, White JF & Oudemans P (eds) 2005 The Fungal Community 3rd edition,, Taylot & Francis., , , , Dix NJ & Webster J 1995 Fungal Ecology, Chapman & Hall, London., , , , Gow NAR & Gadd GM (eds) 1995 The Growing Fungus, Chapman & Hall, London., , , , Redlin SC & Carris LM (eds) 1996 Endophytic Fungi in Grasses and Woody Plants, APS, Press, St Paul, Minnesota, USA., , , , Smith SE & Read DJ 2008 Mycorrhizal Symbiosis (3rd Ed), Academic Press, London., , 5.11 SUGGESTED READING, , , Alexopoulos CJ, Mims CW & Blackwell M 1996, Introductory Mycology (4th Ed),, Wiley, New York., , , , Michael J. Pelczar, JR.; E.C.S. Chan; Noel R. Krieg, Microbiology (6th Ed), Tata, McGRAW-HILL, New Delhi., , 5.12 TERMINAL QUESTIONS, 5.12.1: Long answer type questions:, Q1 Describe range of thallus structure and nutrition in fungi., Q2 Describe distribution and mode of nutrition in fungi as a whole., Q3 Describe various methods of asexual reproduction in fungi., Q4 What is mycelium? Give an account of different types of mycelia met within the fungi., Q5 Give a concise account of sexual reproduction in the fungi., , UTTARAKHAND OPEN UNIVERSITY, , Page 139
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Q6 Describe distinguishing features of each class of fungi., Q7 Give general characters and classification of fungi., Q8 Write an essay on economic importance of fungi., Q 9 Explain the beneficial and harmful roles of fungi., , 5.12.2: Short answer type questions:, Q 1 Write mode of nutrition in fungi., Q2 White notes on(i) Gametangial contact, (ii) Spermatization, (iii)Gametangial Coupulation, (iv) Any five fungal plant disease and their symptoms, (v) Edible fungi, (vi) Role of fungi in industry, (vii)Cell wall and structure of flagella in fungi, , UTTARAKHAND OPEN UNIVERSITY, , Page 140
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT- 6- GENERAL ACCOUNT, HABIT, STRUCTURE, AND METHODS OF REPRODUCTION IN, MASTIGOMYCOTINA, ZYGOMYCOTINA,, ASCOMYCOTINA, 6.1- Objectives, 6.2-Introduction, 6.3-Mastigomycotina-Albugo, 6.3.1-General account, 6.3.2-Habit and Habitat, 6.3.3-Structure, 6.3.4-Reproduction, 6.4-Zygomycotina-Mucor, 6.4.1-General account, 6.4.2-Habit and Habitat, 6.4.3-Structure, 6.4.4-Reproduction, 6.5-Ascomycotina-Saccharomyces and Erysiphe, 6.5.1-General account, 6.5.2-Habit and Habitat, 6.5.3-Structure, 6.5.4-Reproduction, 6.6- Summary, 6.7- Glossary, 6.8- Self assessment question, 6.9-References, 6.10-Suggested Readings, 6.11-Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 141
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 6.1 OBJECTIVES, After reading this unit student will be able:, To know the distinguishing features, general account of Mastigomycotina,, Zygomycotina and Ascomycotina, To study habit, structure , methods of reproduction and life cycle in the representative, genera of Mastigomycotina, Zygomycotina and Ascomycotina, To study the symptoms of disease caused by species of Albugo, Mucor and Erysiphe, and their economic importance., , 6.2 INTRODUCTION, In Whittakar‘s five kingdom system of classification (1969), fungi have been placed under, advanced kingdom (among the five kingdom two are advanced and three are primitive, kingdoms). Earlier in 1937 Gwune- Vaughan and Barnes kept all the three (Mastigomycotina,, Zygomycotina and Ascomycotina) as a class in sub- division named Fungi. This is because at, that time fungi did not get the status of a kingdom. In 1962, Alexopoulos kept all these three, i.e. Mastigomycotina, Zygomycotina and Ascomycotina under subdivision Eumycotina. At, that time, Mastigomycotina was not known because fungi of this sub-division were studied in, separate classes like Chytridiomycetes, Hyphochytridiomycetes, Oomycetes and, Plasmodiophoromycetes of Eucomycotina. However Zygomycotina and Ascomycotina were, known as a classes (zygomycetes and Ascomycetes)., Another system of classification which came after Whittaker‘s five kingdom system, of classification of 1969 is that of Ainsworth, Sparrow and Susman (1973). In his system of, classification Mastigomycotina, Zygomycotina and Ascomycotina got the status of separate, sub-divisions., His classification was based on the presence/absence of motile cells in the life cycle, and also methods of plasmogamy and formation of fertilized diploid structure., Summary of status of Mastigomycotina, Zygomycotina and Ascomycotina, Gwyne- Vaughan and Barnes (1937), , Alexopoulos(1962), , Ainsworth, Sparrow and Susman(1973), , Kingdom : Plantae, , Kingdom : Plantae, , Kingdom: Fungi, , Division: Thallophyta, Sub-division : Fungi, , Division : Myxomycota, Division: Mycota, , Division ; Eumycota*, , Mastigomycotina, Zygomycotina and Ascomycotina as sub-divisions., , 6.3 MASTIGOMYCOTINA- Albugo, 6.3.1 – General account, , UTTARAKHAND OPEN UNIVERSITY, , Page 142
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , The sub-division Mastigomycotina includes fungi which have been classified in one of, the division (i.e. Eumycota) of kingdom fungi. The main features of these fungi are:, Presence of definite cell wall in their somatic structures (a few exceptions), Absorptive mode of nutrition., This sub-division has been divided into classes like Chytridiomycetes,, Hyphochytridiomycetes, Oomycetes etc. on the basis of type of flagella, their number, and place of attachment in the motile cells., Now, the class Oomycetes to which Albugo belongs has been divided into four orders i.e., Saprolegniales, Leptomytales, Lagenidiales and Peronosporales. So the systematic position of, Albugo is:, Fungi, Eumycota, Mastigomycotina, Oomycetes, Peronosporales, Albuginaceae, Albugo, This is the only genus of the family and its species cause a disease called White Rust, Disease, in plants., The genus earlier named as Cystopus., , 6.3.2 – Habit and Habitat, The species of this genus are all obligate parasites on vascular plants e.g., Albugo candida on plant of Crusiferae, A. bliti on plants of Amranthaceae, A. evolvulii on Evolvulus, A. ipomoeae-panduranae on sweet potato, A. portulacae on Portulaca, You may recognize the genus Albugo in nature by observing the symptoms on host plants., The symptoms are:, a) White / creamy small, shining, irregular, raised pustules/ blisters on leaves / stems of, host plants (Fig.6.1)., , Fig.6.1 Infected leaf, , UTTARAKHAND OPEN UNIVERSITY, , Page 143
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , b) Deformed inflorescence of host plants i.e. hypertrophied inflorescences. This is, because of increase in the size of cells of host plants due to infection (Fig.6.2)., , Fig.6.2 Hypertrophied inflorescence, , 6.3.3 – Structure, , , , The thallus of Albugo consists of mycelium which is made up of well developed,, branched, intercellular and coenocytic hyphae. Nuclei are diploid., Hyphal cell walls are made up of cellulose, multinucleate and filled with vacuolated, granular protoplasm. Because the mycelium is intercellular it takes nutrition from host, cells after penetrating their cell walls through minute perforations, and expanding on, the inside of the cells by globose or knob like structure, the haustorium., , 6.3.4 – Reproduction, Albugo reproduces by asexual and sexual methods of reproduction., Asexual reproduction in Albugo takes place by conidia/sporangia., , , Asexual reproduction starts when the hyphae have attained certain stage of, maturity. At this time, the hyphae aggregate or collect at certain places just below the, epidermis of host and produce Short, Thick walled, thin at the tips, Club shaped, At right angles to the epidermis of host, Closely packed vertical structures called conidiophores / sporangiophores., These are in a solid layers / beds., When sporangiophores / conidiophores reach at the certain stage of maturity they, begin to cut-off conidia / sporangia at their tips in the basipetal succession on, below the other i.e. in chain. There is a gelatinous disc (disjunctor cell) between, two conidia / sporangia., , UTTARAKHAND OPEN UNIVERSITY, , Page 144
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , As conidia / sporangia mature they become detached and are free in the space, between the conidiophores / sporangiophores below the epidermis of host., After the formation of sporangiophores / conidiophores and conidia in large, numbers below the epidermis of host, a pressure is created towards the epidermis., This results in the bulging and ultimately bursting of the epidermis over the, growing sorus. Upon bursting of the epidermis conidia / sporangia are released, and form a white crust over the surface of host. Conidia / sporangia when, produced are globose in shape. Later on, these become cuboid or polyhedral due, to pressure during their formation. These are thin walled and multinucleate and, are disseminated by wind, water and any other agency. A large number of conidia, / sporangia die out., , Fig.6.3 Asexual Reproduction in Albugo candida, , There are the two methods of germination of conidia/sporangia:, 1. Direct- when temperature is high, 2. Indirect- when temperature is low., 1. Direct germination is by the germ tube, the asexual spores are called conidia., 2. Indirect germination Takes place by zoospores (showing in Fig.6.3 G-N)., Here the content of asexual spores which are sporangia divides into uninucleate, parts. Each such part gets transformed into uninucleate, biflagellate kidney shaped, zoospores. A papilla develops at the end of the zoosporangium. This papilla gets, transformed into sessile vesicle., Zoospores escape / come out into this vesicle from the zoosporangium. They, swim/move in this vesicle for a short period then lose their flagella, encyst, (change their shape) and germinate by germ tube., 3. Sexual method of reproduction is oogamous which after plasmogamy, karyogamy, and meiosis results in the formation of a resting spore called oospore. Meiosis takes, UTTARAKHAND OPEN UNIVERSITY, , Page 145
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , place at the time of development of antheridia and oogonia. In all species sexual, reproduction is similar but the cytological details of fertilization probably fall into, three patterns which are as follows:, e.g. A. bliti, A. protulacae etc there are many functional nuclei, a large, receptive papilla and a small coenocentrum., e.g. A trapogonosis all nuclei except a single male and a single female, nucleus degenerate after migration into periplasm. There is a small papilla, and a large coenocentrum., e.g. A. candida a pair of functional nuclei fuses after disintegration of all, other nuclei. The size of papilla and coenocentrum is intermediate between, those of the other two types., Following is the method of sexual reproduction based on A. candida:, Gametangia (reproductive structures) are formed when the host is matured or at the, end of the growing season of the host. This is manifested by hypertrophied or deformed, inflorescence of host. Gametangia are antheridia and oogonia, the male and female, respectively. Both develop close to each other and are multinucleate, one celled structures., , Anthredium is club shaped and situated to the side of oogonia i.e. in paragynous, condition and is cut off from the rest of hyphae by a septum., , Oogonium terminal in position (rarely intercalary), and globose in shape. It is also, cut off from the rest of the hyphae by a septum. The nuclei divide by mitotic division. When, mature, the oogonium contains a periplasm and a ooplasm. All the nuclei, except one which, is the only functional nucleus migrate into periplasm and gradually disintegrate. The one, functional nucleus in the ooplasm is called egg or oosphere. Fertilization is paragynous with, the help of a specialized structure called fertilization tube. The fertilization tube grows from, the anthredium, which gets laterally attached to the wall of oogonium and at the point of, attachment a swelling , called receptive papilla , develops over the surface of oogonium . By, piercing the wall of the receptive papilla the fertilization tube enters into the oogonium and, releases only one anthredial nucleus/male nucleus. Now the male nucleus fuses with the egg, or oosphere making it diploid oospore (2n). Soon after the fertilization the coenocentrum is, lost.( Fig. 6.4 A, B, C), , Fig.6. 4 Albugo candida. A, oogonium and anthredium with fertilization tube; B, the oospore, wall has begun to form, the fusion of nucleus; C, the mature oospore, , UTTARAKHAND OPEN UNIVERSITY, , Page 146
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Structure of oospore is globose in shape. It develops thick a wall which is ornamented, and is called exospore. Inner wall is thin and is called endospore. Oospores are released after, the disintegration of host tissue. The oospore enters a resulting stage. After resting period,, and under favourable conditions, the nuclei resume mitotic activity , and the protoplast of the, oospore divides into a large number of uninucleate sections, each of which develops into a, bifllagelate, reniform zoospore. Zoospores are liberated, after cracking of outer thick, exospores, in a thin vesicle which is the expansion of thin endospore. The vesicle after some, time ruptures and then the zoospores swim for some time, then they discard their flagella,, change their shape and encyst and germinate by forming a germ tube (Fig. 6.5). Thus a, diploid mycelium is developed., , Fig. 6.5 Albugo candida D&E, showing germinating oospore and formation of zoospores; F,, Biflagillate kidney shaped zoospore; G, Encysted zoospore; H, Germinating zoospore., , UTTARAKHAND OPEN UNIVERSITY, , Page 147
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.6.9. Showing part of hypha of Mucor sp. (As seen under electron microscope), , 6.4. 4- Reproduction, Mucor reproduces by asexual and sexual methods, , Asexual reproduction in Mucor:, It takes place by sporangiospores, chlamydospores and oidia., , By Sporangiospores – These are endogenously formed non motile asexual spores. These, develop inside a sac like structure called sporangium. Sporangia borne at the tip of erect, unbranched sporangiophores. The sporangiophores of Mucor mucedo are branched., From the hyphae a large number of nuclei with cytoplasm and food material migrate, into the tip. Now gradually such tips enlarge in size and the nuclei divide repeatedly by, mitotic division. Now most of the protoplasmic contents remain in the periphery of the, growing sporangium., So in the centre, there are few nuclei and much less protoplasm. This is followed by, appearance of vacuoles between central and peripheral portions. These vacuoles unite with, one another resulting in the formation of a dome shaped septum separating the peripheral, fertile and central sterile portion. This dome shaped sterile structure is called as columella., After the formation of columella cleavage takes place in the peripheral protoplasm resulting, into numerous small spores with several nuclei. These are sporangiospores., When sporangium is fully matured its wall becomes fragile and disintegrated by, disturbance of air current. Now it ruptures and spores are scattered by air currents., Spores are small, dark colored either ellipsoidal or globose in shape and dry. Each, spore germinate by germ tube when they reach a substratum or host. Germ tube gives rise to a, new mycelium (Fig.6.10). The collumella is persistant structure. It persists even after the, bursting of the sporangium., , UTTARAKHAND OPEN UNIVERSITY, , Page 150
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.6.10. Showing development of sporangiophore and formation of sporangiospores and, collumella within sporangium, , By Chlamydospores : When the mycelium of Mucor is grown in a nutritive liquid, medium, some of the hyphae break up by transverse walls into chains of cells. These cells, round off and develop thick walls around themselves. These are chlamydospores., Chlamydospores are resting spores. Each such spore under favourable condition gives rise to, new mycelium (Fig. 6.11)., , Fig.6.11. Showing Chlamydospores, , By Oidia: species like Mucor racemosus if cultured in high sugar concentration, their, hyphae breakup into short segments called oidia. These oidia may bud like yeast and called, torula condition (Fig. 6.12)., , UTTARAKHAND OPEN UNIVERSITY, , Page 151
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig. 6.12 Showing Oidia, , Sexual Reproduction: Sexual reproduction requires the presence of two physiologically, different and compatable mycelia designated by + and – signs. These physiologically, different hyphae develop after the germination of physiologically different sporangiospores., When such two compatable hyphae (+ and -) come in contact with each other,, copulating branches (progametangia) are formed. This is followed by the flow of cytoplasm, and many nuclei into the contacting tips of these organs. The progametangia are separated by, the rest of hyphae due to the formation of septa near the tip. Now there are two cells i.e. a, terminal cell called gametangia and the other one is the suspensor cell (Fig. 6.13 & 6.14)., , Fig. 6.13 Formation of progametangia, , At the point of the contact, the walls dissolve and mixing of the two protoplasts, takes place, which is followed by pairing of compatible nuclei (+and -). The two nuclei fuse, and form diploid nuclei. Remaining nuclei probably disintegrate (Cutter, 1942b). The new, cell which is formed by the two copulating gametangia enlarges in size; its wall thickens with, rough warty surface, and a zygospore is formed., , UTTARAKHAND OPEN UNIVERSITY, , Page 152
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig. 6.14 Showing formation of Zygospore, , Zygospores undergoes for a resting period. Now meiosis takes place when, conditions are favourable. The outer wall splits and inner one grows out to form a hypha like, germ tube or pro mycelium. It grows erect to form sporangiophore bearing a sporangium., This type of sporangium is also called germ sporangium or zygosporangium. These, structure produce spores after meiosis. Thus the spores are haploid. These spores after, reaching a suitable substratum or host, form new haploid mycelia., , Fig. 6.15 Life cycle of Mucor, UTTARAKHAND OPEN UNIVERSITY, , Page 153
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 6.5 ASCOMYCOTINA- Sacchromyces and Erysiphe, 6.5.1 General account, In this section, characteristics of Ascomycotina in the reference of Saccharomyces and, Erysiphe will be discussed., , , , , , , Ascomycetes are the fungi, in which spore resulting from karyogamy and meiosis are, enclosed in a sac like cell called ascus. The spores are ascospores which develope by, free cell formation method., These fungi do not have motile cells., Chitin is the chief composition of the cell wall. There is no cellulose., There is short dikaryotic stage interspread between plasmogamy, karyogamy and, meiosis., , Saccharomyces and Erysiphe are two fungi of this class which will be discussed in detail:, , 6.5.1.1-Saccharomyces, , , , , , , , Mycota, Eumycotina, Ascomycetes, Hemiascomycetedae, Endomycetales, Saccharomycetaceae, Sacchromyces, , 6.5.1.2- Habit and Habitat, It is commonly known as Yeast. These fungi are widely distributed over the surface of earth ,, particularly over such substratum which are rich in sugar e.g. nectar of flowers, surface of, fruits. That is why the name Saccharomyces (Saccharum =sugar + myketes = fungi) is given., Species also grow in soil, animal excreta and milk etc. Saccharomyces has useful as well as, harmful importance. The useful property is, their role in fermentation. Therefore these fungi, are economically important in bakery and brewery. This useful property of Saccharomyces if, not handled properly, causes loss to the industrialists. They also destroy cheese, causing bad, flavor. Common species of Yeasts are:, Saccharomyces cerivisiae, Saccharomyces apiculatus, Saccharomyces frnctuum, , 6.5.1.3 Structure, In case of Sacchromyces the vegetative body is unicellular not made up of hyphae., Sometimes, many cells of Yeast unite in chain and form a pseudomycelium. Thus, this genus, is polymorphic. This nature depends on the type of medium in which the fungus is growing., , UTTARAKHAND OPEN UNIVERSITY, , Page 154
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig. 6.16 Structure of Yeast cell, , Fig. 6.17 Pseudomycelium, , The Yeast cell is colourless in nature but when it is grown in the medium in laboratory, the, cells may be pink, white or cream colored. Normally shape of cell is spherical, oval or, cylindrical. There is a definite thin cell wall composed mainly of chitin along with, carbohydrates, mannan and glucan. There are two layers in a cell wall. The outer one is dense, and approximately 0.05 micron thick, and an inner layer which is less dense and nearly 0.2, micron thick, containing microfibrils. Inside the cell wall, there is cytoplasm which is, granular. In mature or old cells the cytoplasm is differentiated into an outer ectoplasm and an, inner endoplasm. Ribosomes, mitochondria and endoplasmic reticulum are also found in the, cell. Glycogen, oil globules and protein particles are the reserve food materials. There are, , UTTARAKHAND OPEN UNIVERSITY, , Page 155
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , different views about the nature of vacuole, nucleus and nucleolus (Fig 6.16). The views are as, follows:, Ist view – The centrally placed hyaline area is nucleus and there is a deeply stained body to, one side of it is the nucleolus. The central area is not a vacuole. There is a centromere on one, side of nucleus., IInd view– Central hyaline area is a vacuole and not a nucleus. Nucleus is present opposite to, it which was identified as nucleolus by the supporters of Ist view., IIIrd view– Nucleus is surrounded by a definite membrane and is distinct from vacuole., , 6.5.1.4 Reproduction, Saccharomyces reproduces by two methods, i.e. Asexual and Sexual., , Asexual reproduction, 1) Budding: This method is adopted when there is abundant food / nutrients. During, budding, nucleus of mother cell divides mitotically. This is followed by appearance of, small growth over the surface of the vegetative cell called bud. One of the nuclei, passes into this bud, and the bud is separated from parent cell by the formation of a, wall between the two cells. Thus there is formation of new individual. This process, continues and at times the bud may also start forming new buds. This results, formation of a pseudomycelium (Fig 6.17, 6.18)., , Fig. 6.18. Budding in Yeast, , 2) Endospore formation- This process is adopted when there is scarcity of food or, there is chance of desiccation. The protoplasm of vegetative cell divides usually into, four portions. Later on, each portion gets surrounded by a thick wall. These are, endospores. When conditions are favorable for growth, they germinate and form a, chain of cells., , Sexual reproduction – The process takes place by conjugation between two haploid cells., Cells may be similar or dissimilar and are called gametangia. So, there are no specialized sex, organs. This process is termed as hologamy. The diploid zygote itself function as ascus and, produces ascospores after meiosis. Ascospores are generally globose or ovoid and differ in, number. Ascospores upon liberation multiply by budding to produce haploid cells. Zygote, UTTARAKHAND OPEN UNIVERSITY, , Page 156
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , may also bud forming large number of diploid cells. Each diploid cell behaves as ascus (Fig, 6.19)., , Fig.6.19. Sexual reproduction in Yeast, , Life cycle of S. cerevisae is haplodiplobiontic type. The haploid and diploid phases are, equally well represented. Students therefore there is clear alternation of generations in this, species of Yeast (Fig.6.20)., , Fig. 6.20. Haplodiplobiontic life cycle of Sacchromyces cervisae, , 6.5.2.1 Erysiphe - HABIT AND HABITAT, UTTARAKHAND OPEN UNIVERSITY, , Page 157
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , The systematic position of Erysiphe is as follows:, , , , , , , , Mycota, Eumycotina, Ascomycetes, Hamenoascomycetidae, Pyrenomycetes, Erysiphe, , Erysiphe is an important fungus and causes powdery mildew disease. Some, mycologists classify it under Plectomycetes because of completely closed nature of ascocarp, (fruiting body),while others give more emphasis to the position of asci inside the ascocarp, and place it under Pyrenomycetes. Thus the difference in classifying this fungus is just, because of the different criteria taken by the mycologists., Many species of this genus attack the host and develop white powdery coating over, the surface of host, hence the name powdery mildew. Following are some of the species of, this genus:, Erysiphe polygonii, Erysiphe graminis, Erysiphe cichoracearum, , 6.5.2.3 STRUCTURE, Thallus of Erysiphe is made up of hyphae and which are hyaline abundantly present over the, surface of the epidermis of host. The hyphae send haustoria into the epidermis of host for, absorbing nutrients. Haustoria arise from the lobed swellings of the hyphae adjacent to leaf, surface and are called appresoria. In Erysiphe polygoni haustoria are almost knob shaped and, in E. graminis these are finger like or branched. But in any case haustoria are restricted only, in the epidermal cells of host (Fig.6.21)., , 6.5.2.4 REPRODUCTION, Erysiphe reproduces by asexual and sexual methods. Asexual method of reproduction is, commom by conidia. It starts after few days of infection when the hyphae produce erect,, long, septate conidiophores. The upper most cell is called generative cell. This cell produces, conidia. The conidia in some species are abstricted before the maturation of next one, while, in other species conidia are not abstricted and remain attached to each other and thus form, chain of conidia. These are hyaline, one celled and may vary in shape. Mostly the shape is, oval or cylindrical with rounded edges. They are disseminated by wind, water, insects or, other agencies., , UTTARAKHAND OPEN UNIVERSITY, , Page 158
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.6.21 Showing mycelium, conidia and haustoria found in genus Erysiphe, , The conidia germinate and do not require free water for germination. The distal end of each, conidium develops a flat appressorium over the surface of the host. A peg-like structure, develops from appressorium and penetrates the epidermis of the host. The tip of the peg like, projection swells resulting in the formation of a vesicle which gives rise the finger like, haustorium. Asexual reproduction takes place during growing season., , Sexual Reproduction, At the end of growing season of host, black colored round structures are seen on the, white powdery surface of the host. These are the symptoms of the onset of sexual, reproduction. The black structures are cleistothecia. Newly formed cleistothecia are first, white, then turn orange, reddish brown and finally black when mature., Most of the species are homothallic except few i.e. E. graminis which is heterothallic., The uninucleate gametangia develop from the hyphae which are closely present. Male, gametangium is more slender than the female gametangium ie. the ascogonium. These are so, close to each other that they press each other. Mycologist disagree as to the cytological, details which follow. But probably the further course of development follows the usual, pattern. The antheredium nucleus passes into the ascogonium through a pore. Process of, karyogamy is postponed until the ascus mother cell is formed. Many sterile hyphae develop, from the base of ascogonium and surround the sex organs completely. The surrounding, sheath is thick and multilayered., , UTTARAKHAND OPEN UNIVERSITY, , Page 159
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.6.22 Showing gametangial contact and formation of ascus, , The two nuclei lying in the ascogonium divide to form 5 to 8 daughter nuclei and due, to formation of septa, the ascogonium becomes 4-5 celled. The cell just below terminal cell, i.e. penultimate cell remains binucleate and rest of the segments remain uninucleate. The, penultimate cell forms hyphae called ascogenous hyphae. Now the binucleate cells of the, ascogenous hyphae enlarge and the fusion of nuclei takes place. The diploid nucleus divides, by meiosis. This is followed by mitotic division, which results in the formation of eight, haploid nuclei. Each nucleus gets surrounded by a small amount of cytoplasm and a wall., There are eight haploid ascospores. In E. cichoracearum, each ascus contains only 2-3, ascospores. Ascospores are hyaline, one- celled, uninucleate and ellipsoidal in shape., Ascospores remain inside ascocarp within asci. The ascocarp is called cleistothecium, (Fig.6.22)., The cleistothecium is a sub-globular or round, completely closed structure. Large, number of hyphae surrounds the surface of cleistothecium. These hyphae are called, appendages, which are either simple or branched (Fig.6.23)., , UTTARAKHAND OPEN UNIVERSITY, , Page 160
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.6.23 Showing Cleistothecium, , The mature cleistothecium remains dormant throughout the winter season and with the onset, of the spring, the asci absorb water and swell resulting in the irregular rupturing of the, peridium. In E. graminis the peridium splits in the equatorial plane by transverse splitting., Asci absorb moisture, swell and then burst releasing the ascospores. These are disseminated, by wind. On reaching a suitable host germinate and produce haploid mycelium., , Fig.6.24 Showing Life cycle of Erysiphe, UTTARAKHAND OPEN UNIVERSITY, , Page 161
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 6.6 SUMMARY, Status of the Mastigomycotina, Zygomycotina and Ascomycotina in fungal world., Mastigomycotina, Zygomycotina and Ascomycotina have got the status of subdivision after the five kingdom classification of Whitaakar(1969). All the three groups, show a definite cell wall., Mastigomycotina have flagellated fungi., Zygomycotina and Ascomycotina are non- flagellated fungi., Mastigomycotina after plasmogamy, karyogamy and meiosis produce oospores, formed from fertilized egg., Zygomycotina produce zygospores after plasmogamy, karyogamy and meiosis. The, fusing gametangia may be equal or unequal., Ascomycotina produce ascospores after plasmogamy, karyogamy and meiosis inside a, sac like structure called ascus., Albugo is an obligate genus causes a disease called white rust of crucifers. It produces, symptom of disease on host which differ during asexual and sexual stages. Symptoms, of asexual stage are recognized by white pustules on leaf of host, while symptoms of, sexual stage are recognized by hypertrophied inflorescence of host. Mycelium of, Albugo is diploid and is made up of hyphae which are coenocytic , intercellular and, produce knob shaped haustoria for absorption of food from host. It reproduces both by, asexual and sexual methods. Asexual reproduction takes place by conidia/sporangia, borne on conidiophores. Asexual spores germinate by two methods. Sexual, reproduction is oogamous resulting into a diploid thick walled oospore. Meiosis takes, place at the time of formation of gametangia., Mucor has species both parasitic and saprobic . Mucor is commonly known as black, mold. Species spoil food, particularly rich in carbohydrates. Some species are, pathogenic. Mucor has mycelium made up of branched haploid hyphae. Its reproduces, by asexual and sexual methods. Asexual reproduction is by sporangiospores,, chlamydospores and oidia. Sexual process results in formation of diploid thick walled, spore called zygospores. Due to fusion of two gametangia phenomenon of, heterothallism has been reported in the species of this genus., Saccharomyces commonly called Yeast, is of great industrial importance. Species are, used in bakery and brewing. It is one celled, colourless in nature. There is controversy, about the nature of vacuole present in the cell. It reproduces by asexual and sexual, methods. Asexual reproduction takes place by budding and endospore. Sexual, reproduction by conjugation in between two haploid cells i.e. hologamy. Sexual, reproduction results in the formatation of ascospores inside the ascus., Erysiphe is also parasitic genus. It causes a disease known as Powdery Mildew on, economically important crops. It consist of superficial mycelium which grows on the, surface of leaf of host and only haustorium enters into the epidermis of host for the, absorption of food., , UTTARAKHAND OPEN UNIVERSITY, , Page 162
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Asexual reproduction is by conidia on short conidiophores. Sexual reproduction results in the, formation of ascospores inside asci. These are borne inside the cleistothecium. These fruiting, bodies have a number of appendages on its surface., , 6.7 GLOSSARY, Achlorophyllous: lacking chlorophyll., Aeciospores : a binucleate spore produced in an aecium., Aecium : a structure consisting of binucleate hyphal cells with or without a peridium that, produces spore chain consisting of aeciospores alternating with disjuncture cells, following, the successive conjugate division of the nuclei., , Antheridium : a male gametangium., Appresorium : a flattened, hyphal, organ from which a minute infection peg usually grows., and enters the epidermal cell of the host., , Ascocarp : a fruit body containing asci., Ascospores : a meiospore borne in an ascus., Ascostroma : a stromatic ascocarp bearing asci directly in locules within the stroma., Ascus : a sac like cell generally containing a definite number of ascospores (typically eight), formed by free cell formation usually after karyogamy and meiosis, characteristic of class, Ascomycetes., , Aseptate : lacking cross walls., Asexual : reproduction not involving karyogamy and meiosis., Budding : the production of a small outgrowth (bud) from a parent cell; a method of, asexual reproduction., , Chlamydospores : a thick walled thallic conidium that generally functions as a resting, spore., , Coenocytic : a non – septate referring to the fact that nuclei are embedded in the cytoplasm, without being separated by cross-walls., , Collumella : a sterile structure within a sporangium or other fructication, often an extension, of the stalk., , Conidiophore : a simple or branched hypha arising from a somatic hypha and bearing at it, stip or side one or more conidiogenous cells., , Conidium : a non-motile asexual spores usually formed at the tip or side of a sporogenous, cell; in some instance a pre – existing hyphal cell may be converted to a conidium., , UTTARAKHAND OPEN UNIVERSITY, , Page 163
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , B. 1. Basipetal succession 2. Coenocytic 3. Haploid 4. Exposed 5. Zygospore 6. Unicellular, 7. Cleistothecium 8. Black mold, Yeast, , 6.9 REFERENCES, , , , , , , , , , , Alexopoulos C.J., Mims, C.W. and Blakwell, M. 1996. Introducting Mycology 4 th ed., John Wiley, N.Y., Anisworth, G.C. 1964. A general purpose classification of fungi Bibl. Syst. Mycol. No. 1:, 1-4., Anisworth, G.C. 1973. Introduction and keys to higher Taxa. In: The Fungi. An, Advanced Treatise. ( G. C. Anisworth, F. K. Sparrow and A. S. Sussman,, eds.).International, Oxon, U.K., Daya, R and Raizada, B.B.S 1998-99 Introduction to Fungi Vishal Publications: India., Dube, H.C. 2013. An Introduction to Fungi 4th ed. Scientific Publishers (India)., Hawkswarth , D.L. et al. (1995) Aniswarth and Bisby‘ Dictionary of Fungi CAB, International, Oxon, U.K., Kirk, P.M. et al. 2008 Aniswarth and Bisty‘s Dictonary of fungi 10th ed.) CAB, International, Oxon, U.K., Kirk, P.M. etal. 2008 Anisworth and Bisby‖s Dictionary of the Fungi (10th ed.) CAB, International, Oxon, U.K., , 6.10 SUGGESTED READING, , , , , , , , , , , , , , , Ajello, l. d. ET AL. 1976. The Zygomycetes saksena vasiformis as a pathogen of humans, with a critical review of the etiology of zygomycotina. Mycologia. 68: 52-61., Alexopoulos C.J., Mims, C.W. and Blakwell, M. 1996. Introducting Mycology 4 th ed., John Wiley, N.Y., Alexopoulous C.J. 1962 Introductary Mycology 2nd ed. John Willey and Nysans., Barnett, H. L. 1955 Illustrated genera of Imperfect fungi. Burgers Publ. Co. Minneapolis., Bilgrami, K.S and Dube, H.C.1976 A text book of modern Plant Pathology, Vikas, Publishing House pvt. Lmtd. New Delhi., Daya, R and Raizada, B.B.S 1998-99 Introduction to Fungi Vishal Publications: India., Dube, H.C. 2013. An Introduction to Fungi 4th ed. Scientific Publishers (India)., Moore, R.T. 1964 Fine structure of Mycota. 12. Karyochorosis somatic nuclear division, in candyceps milivaris Z elforsch. 63: 221-237., Pandey, S.N. and P.S. Trivedi. A Text Book of Botany Vol. I. 10th revised ed. 1994., Vikas Publishing House Pvt. Ltd. New Delhi., Raper, J. R. 1954. Life cycles, sexuality and sexual mechanism in fungi. In: sex in, microorganism (D.H Wenrich, I.F. Lewis and J. R. Raper eds.). Ama. Assoc. Adv. Sci. 3:, 565- 589., Smith, G. M. 1955. Cryptogamic Botany. Vol. I. Mc Graw. Hill Book Co. NY., Waksman, S.A. 1917. Is there any fungus flora of the soil? Soil Sci. 3:565-589., , UTTARAKHAND OPEN UNIVERSITY, , Page 165
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 6.11 TERMINAL QUESTIONS, 1. Mastigomycotina, Zygomycotina and Ascomycotina have been classified under which, system of classification? Give a detailed account., 2. What are chief characteristin of Ascomycotina and Zygomycotina?, 3. How Albugo reproduces by asexual and sexual methods of reproduction?, 4. What are symptoms of infection caused by Albugo?, 5. What is torula conditions of Mucor?, 6. How does zygospore formation takes place in Mucor?, 7. Give an illustrtraited account of sexual reproduction in Mucor with special reference to, heterothallism., 8. Name the disease caused by the species of Erysiphe. Discuss its sexual stages of, reproduction., 9. Write characteristic features of Saccharomyces., 10. Discuss method of reproduction in Saccharomyces., , UTTARAKHAND OPEN UNIVERSITY, , Page 166
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-7 GENERAL ACCOUNT, HABIT, STRUCTURE, AND METHODS OF REPRODUCTION IN, BASIDIOMYCOTINA, DEUTEROMYCOTINA AND, MYCOPLASMA, 7.1- Objectives, 7.2-Introduction, 7.3-Basidiomycotina-Puccinia and Agaricus, 7.3.1-General account, 7.3.2-Habit and Habitat, 7.3.3-Structure, 7.3.4-Reproduction, 7.4-Deuteromycotina-Alternaria, 7.4.1-General account, 7.4.2-Habit and Habitat, 7.4.3-Structure, 7.4.4-Reproduction, 7.5-Mycoplasma-General account, 7.6- Summary, 7.7- Glossary, 7.8- Self assessment question, 7.9-References, 7.10-Suggested Readings, 7.11-Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 167
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 7.1- OBJECTIVES, The objectives of this unit are to get you familiar about the differences between, Basidiomycotina, Deuteromycotina and Mycoplasma. These are as follows:, , , , , , , , Basidiomycotinaincludes fungi which reproduce both by sexual and asexual methods, of reproduction, while Deuteromycotina group includes imperfect fungi which, reproduce only by asexual methods., Mycoplasma are prokaryotic organisums and do not resemble fungi belonging to, Basidiomycotina or Deuteromycotina., After reading this unit you will know about the living place of members of these, groups, the variations in their vegetative / somatic structures as well as the methods of, reproduction., You will know the disease caused by Puccinia, Agaricus and Alternaria., , 7.2 INTRODUCTION, In unit 6.2The status of Mastigomycotina, Zygomycotina and Ascomycotinawas, described in few important systems of classification of fungi . In this unit, the status of, Basidiomycotina and Deuteromycotina will be discussed., These two groups were also treated as a class of sub-division fungi by GwuneVaughan and Barnes 1937. Then according to Alexopoulus system of classification (1962),, these were also treated as class, but of sub-division named Eumycotina. In 1969,, Basidiomycotina and Deuteromycotina also got the status of a separate sub-division when, Whittakar system of five kingdom classification was accepted., , 7.3 BASIDIOMYCOTINA, (A) Puccinia, 7.3.1 General account, In this section you will learn about the classification of Basidiomycotina with particular, reference to Puccinia and Agaricus., , , , , , , , Basidiomycotina are those fungi in which spores resulting from plasmogamy,, karyogamy and meiosis are borne on club shaped structure called basidium. Motile, cells are absent in the members of this group., Dolipore septa occur in most Basidiomycetes., There is long dikaryotic stage interspread between a Plasmogamy, karyogamy and is, represented by extensive dikaryotic mycelium which produces sporophores, (Basidiocarps)., Puccinia and Agaricusare two important fungi belonging to basidiomycotina. The, systematic position of Puccniais as follows:, , UTTARAKHAND OPEN UNIVERSITY, , Page 168
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , , , , , BSCBO-101, , Mycota, Eumycotina, Basidiomycetes, Hetrobasidiomycetidae, Uredinales, Puciniaceae, Puccinia, , 7.3.2 Habit and habit, Puccinia is very important and widely distributed genus of this group. It includes about, 700 species from India Most of the species are obligate parasites. The fungus is, characterized by its spores which are orange/ black in colour and this is the reason that the, disease caused by various species is called Rust disease. The fungus attacks important, crop plants e.g. oat, rye, barley and wheat etc. Some important species are as follows:, Puccinia graminis, - Black or stem rust, P. recondita, - Brown rust, P. striiformis, - Stripe rust or yellow rust, The most important species of the genus is Pucciniagraministriticiand is being taken as an, example to explain the structure and reproduction of the genus. It is obligate parasite an, the fungus is heterocious, polymorphic and macrocyclic. The meanings of all above, adjectives used for this species are as follows:, , Obligate: Life cycle is completed only on hosts., Parasite: Life cycle is completed on host., Heteroecious: Life cycle is completed on two entirely different hosts i.e., , , , Barberry (Barberis vulgaris) which is a secondary alternate host., Wheat (Triticumvulgare) which is a primary host., , Polymorphic:, , Life cycle shows five distinct stages at regular intervals and are, represented by five types of spores. These are as follows:, , Stage I-, , 0-stage – represented by Spermogonia/ Pycnia/ pycnidia containing:, , spermatia/ pycnidiospores = Male reproductive structure, receptive hyphae/ flexnous hyphae = Female reproductive structure, Stage II1-stageAecia/, Aeciospores/, Aecidia, Aecidiospores, , Stage III-, , Stage IV-, , 2-stage, , 3-stage, , Uredia/, , Uredospores/, , Uredosori, , Uredospores, , Telia/, , Teleutospores/, , Teleutosori, , Teliospores, , UTTARAKHAND OPEN UNIVERSITY, , Page 169
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , Stage V-, , 4-stage, , BSCBO-101, , Basidia/, , Basidiospores/, , Pro-mycelium, , sporidia, , The Stage I, II and V occur on Barberry host (which is an alternate host of the pathogen),, while, the stage III and IV occur on the primary host i.e. wheat plant (Fig. 7.1)., , (i), , (ii), , (iii), Fig.7.1-Showing Symptom of Rust on Wheat stem (i & ii) and Berberry leaf (iii), , 7.3.3 Structure, Mycelium well developed and consist of hyphae which are septate, branched moderately., There are two types of hyphae. Primary hyphae are those which form after the germination, of basidiospores. These primary hyphae are unicellular and multinucleate in the beginning, but due to formation of septa they become multicellular and uninucleate. These are haploid, and are of two strains. One is represented by + ve sign and other by – ve sign. These, hyphae form monokaryotic mycelium. Secondary hyphae are multicellular and binucleate, (n+n),form dikaryotic mycelium., The monokaryotic mycelium grows on Barberry (secondary host) and secondary mycelium, on wheat (primary host)., Both types of mycelia are not very deep seated but they grow close to epidermis of, host., , 7.3.4 Reproduction, Reproduction and life cycle of Puccinia graminis is represented by following stages:, UTTARAKHAND OPEN UNIVERSITY, , Page 170
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 0-Stage- I Represented by spermogonia containing male (spermatia) and, female (receptive hyphae) structures., Reproductive organs of P. graminis are spermatia (Pycniospores/ Pycnidiospores), and receptive hyphae/ flexous hyphae, the male and female structure respectively. These, are borne in spermogonia / pycnia/ pycnidia. These are haploid. Spermogonia are, produced on upper surface of Barberry leaf by primary monokaryotic mycelium.The, primary monokaryotic mycelium which develops after the germination of haploid, basidiospore( + or – strains).Thespermogonia are of two types. One containing all the, structures of one strain or factor (+) and the other having all the structures of opposite, strains or factor (-). In nature spermagonia of opposite strains or factor are produced close, together., The basidiospores germinate on the surface of leaf of barberry in the presence of, moisture. The spores produce germtube which penetrate directly into the epidermis of leaf., After penetration of germ tube, it freely branches and forms haploid monokaryotic, mycelium. The mycelium carries either (+) or (-) factor / strains which depends upon the, strain of basidiospores. The mycelium now vigorously grows producing dense mats of, uninucleate hyphae. These are primordial of the spermogonia (pycnia / pycnidia). The, formation of spermogonia may be observed by small yellow or red patches on the upper, surface of the infected leaves., The mycelium which is not involved in the formation of spermogonia penetrates, deep towards the lower epidermis of leaf of Barberry. A mature spermogonia is small,, oval to flask shaped structureThe wall of spermogonium is called peridium and it is made, up of pseudoparenchymatousplectenchyma. There is an opening called ostiole which, opens at the leaf surface. From the base of spermogonium arise a large number of, uninucleate, unicellular hyphae called spermatiaphores. These have rounded base and, blunt tips (Fig.7.2)., The spermatiophores cut off from their tips a large number of male cells called, spermatia or pycnia orpycnidia. Spermatia are unicellular, globose and uninucleate and, are formed in chain. From the neck of spermogonia arise two types of hyphae, one is, called flexous hyphae or receptive hyphae. These are female reproductive structures., Receptive hyphae are also uninucleate one celled with flat base and pointed tips. The other, type of hyphae aresterile hyphae called paraphysis. Receptive hyphae and paraphysis, grow out of the epidermis., , UTTARAKHAND OPEN UNIVERSITY, , Page 171
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.7.2: Showing Spermagonium of wheat, receptive hyphae (RH), spermatium (S), and, wheat epidermis (E), , Plasmogamy- In Pucciniagraminis process of plasmogamy is with the help of flies. The, flies or insects get attracted towards the sweet nectar of leaf and when they suck the nectar, some spermatia stick to their legs and proboscis.When such insects / flies visit another, spermogonia on the leaf, the spermatia are taken away by the receptive hyphae of these, spermogonia. When the spermatia contact the receptive hyphae or of spermogonia of, opposite strain, the dikaryotization takes place resulting in dikaryotic receptive hyphae., The spermatia of one strain enter into the receptive hypha of opposite strains through a, pore which develops at the point of contact between them (Fig.7.3)., , Fig.7.3: Showing process of Plasmogamy, , 1- Stage -II Represented by Aecia and aeciospores (Aecial stage) on barberry, leaf., At the time of spermatization which results in dikaryotization, the primary, monokaryotic mycelium penetrates entire leaf of berberry and hyphae near the lower, epidermis form a number of aecial primordial. Spermatial nuclei which passes from, spermatia into receptive hyphae pass through the septal perforation of mycelium and reach, the cells of aecial primordial, rendering them binucleate. It has been demonstrated that the, aecialprimordia fail to grow further unless and until spermatization takes place., , UTTARAKHAND OPEN UNIVERSITY, , Page 172
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.7.4:Showing Aecia & aceiospores, , Aecia are globose and completely closed structure. The wall or aeciumis called, peridium and made of pseudo parenchymatous fungal tissue. The cells present at the base of, aecia are called aeciospores mother cells. These are the first binucleate cell in the life cycle., Aeciospore mother cells divide and form aeciospores at the terminal position alternating with, sterile cells called disjunctor cells. Aeciospores are polyhedral, unicellular and binucleate., They are formed in chains. Peridium covers the entire aecial cup but as the cup grows and, aeciospores are formed the pressure is created resulting into breaking up off the peridium., Then the aeciospores are released. The broken part of the peridium lies over the surface of, lower epidermis and called lip of the peridium. Aeciospores are disseminated by wind and, germinate under favourable conditions on a susceptible primary host i.e. wheat plant and, produce binucleatemycelium. But the aeciospores fail to grow further if they do not reach a, grass host. So, a binucleate aeciospores produced on barberry leaf can grow further only on, wheat host (Fig.7.4)., , 2- Stage –III Represented by uredia forming uredospores on wheat plant., In the month of March / April (spring season) reddish orange coloured spots / pustules, appear over the leaf of wheat. These are uredia or uredosori. Uredia are made up of secondary, dikaryotic mycelium which develops after the germination of aeciospores on wheat leaf. The, secondary dikaryotic mycelium grows, ramifies just below the epidermis of wheat leaf. From, the base of uredosori arise a large number of sporophores which bear at their apices oval, thick walled, brown coloured, binucleate, one celled, stalked urediospore Each, urediosporesposses four germ pores which are equatorially arranged. Outer wall of, urediospore is thick and ornamented/rough while inner wall is smooth. Uredospores remain, compactly arranged with in the uredosori. As the spores mature, pressure is exerted towards, the growing epidermis of host which ultimately breaks away releasing the spores above the, surface of epidermis. The germ tube of uredospore does not enter directly into the host cells., The tip of the germ tube swells up form an elongated appresorium. The appresorium is cut, off from the spore and sends fine hyphae into the stomata. These hyphae grow and ramify, within the intercellular space of host tissues., UTTARAKHAND OPEN UNIVERSITY, , Page 173
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , As soon as the spores mature (3-4days) they germinate by forming germ tube and the, mycelium again infect the wheat host on which they were produced. Thus the spores spread, the disease from plant to plant and from field to field. That is why the uredospores are also, called repeating spores (Fig.7.5)., , Fig.7.5: Showing Uredosorus in various stage of development, , 3-Stage –IV Telia / teleutosori forming teleutospores, About the time wheat grain is maturing instead of brown/ orange spots or pustules black, coloured streaks develop on the leaf of wheat host. These are telia / teleutosori., , Fig.7.6. Showing bicelled Teleutosorus in various stage of development, The dikaryotic mycelium collects below the surface of epidermis of wheat stem and, forms teleutosori in the same manner as it formed uredosori on leaf of wheat. Sporophores, produce at their tips bicelled, thick walled, dikaryotic, stalked teleutospores. Each cell, contains a pair of nuclei of opposite strains (+,-). Tip of teleutospore is either rounded or, pointed. There are two germpores present in spore, one at the tip of upper cell and one at the, junction of two cells. The two nuclei (+,-) of each cell fuse together making the spores, diploid. The Teleutosporedo not germinate immediately. They survive during winter and, germinate in next spring. Thus over wintering takes place in diploid teleutospores (Fig.7.6)., , UTTARAKHAND OPEN UNIVERSITY, , Page 174
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 4-Stage –V Represented by promycelium forming basidium and basidiospores, Early in the spring each cell of the teleutosporegerminates and produce pro mycelium into, which passes the diploid nuclei where it undergoes for meiosis and for four haploid nuclei, (n)., Nowthe pro mycelium becomes dividedinto four uninucleate cells. From the side of, which a single small tube the sterigmata on which basidiospore is fomed. The nucleus and, cytoplasm moves into uredospore through sterigmata. P.graminis is hetrothallic and out of, the four basidiospores thus formed two one of (+) strain and other two are of (-) strain. The, basidiospores are one celled, uninucleate, stalked, oval in shape and brown yellow in colour., Soon after their formation the basidiospores are forcibly ejected by water droplet method ane, are carried away by the wind. If they fall on a barberry plant (host) then only they germinate, and produce mono karyotic primary mycelium of either + or – strains depending upon the, nature of basidiospore from which its germinates (Fig.7.7)., , Fig.7.7: Showing bicellular teleutospore (A), Stages in the germination of teleutospore (B,C,D), and Germinated teleutospore (E), , UTTARAKHAND OPEN UNIVERSITY, , Page 175
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 8(A), , 8(B), Fig.7.8: (A) & (B) Showing Life Cycle of Puccinia graminis triticii, , (B) General account- Agaricus, UTTARAKHAND OPEN UNIVERSITY, , Page 176
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 7.4.2 Habit and habitat, Species of Agaricus grows on damp, moist places, rotten wood, dead and decaying organic, matters, on manure piles and on well manured grasses i.e. Lawns., , 7.4.3 Structure, Vegetative bodies are made up of mycelium whose hyphae pass through two phases., Phase I – Is represented by monokaryotic mycelium. This is primary mycelium, whose hyphae are short lived much branched septate. These hyphae are loosely tangled and, grow below substratum. Cells contain highly vacuolated granular protoplasm. These are, uninucleate and have oil globules. This mycelium is produced by the germination of, basidiospores. Primary mycelium contains two types of strains represented by + ve and – ve, signs., Phase II – is represented by the mycelium whose cells are binucleate. This develops, after the dikaryotization of cells of hyphae of primary mycelium., , Fig.7.11. Showing hypha bearing fruiting bodies of 1st, 2nd and 3rd year, , These are persistant and survive on the substratum for very long duration. It has a, tendency to grow in all direction. It consist of septate, profusely branched hyphae. Hyphae, have dolipore septum through which connectivity of cells is maintained. It forms, rhizomorphs and fruting body i.e. basidiocarps (Fig.7.9, 7.10, 7.11)., , 7.4.4 Reproduction, Agaricus reproduce by asexual method of reproduction by forming chlamydospores., Sexual reproduction result in the formation of basidiospores after plasmogamy, karyogamy, and meiosis., Plasmogamy by somatogamy between the cells of compatible hyphae. Most of the, species are heterothallic. Heterothallic species may be both bipolar or tetrapolar. A., compestris is bisporous and homothallic., , UTTARAKHAND OPEN UNIVERSITY, , Page 178
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Some times dikaryotization may also occur due to oidization i.e. fusion of protoplast, of cells of hyphae and an oidium of opposite strains (+ve and –ve). The new dikaryotic cell, grows, ramifies and forms dikaryotic mycelium. The mycelium spreads below the, substratum and at certain places forms small knot like structures called hyphal knots., When the surface of substratum is moist the hyphal knots come above the substratum, as small globose or ovoid structures constituting the ‗button stage‘ of the life cycle., Button grows and its upper end enlarges resulting into the distinct regions. The upper, and low parts. The upper part developing into pileus or cap and lower into stipe or stalk. At, the junction of upper and lower parts to cavities appear consisting of downwardly growing, hyphae., These cavities are called pre lamellar cavities. From the roof of these cavities the, downwardly growing hyphae push themselves into the gill cavities to form a series of, radiating plates called gills. The margin of the button is connected with the stalk by a, membrane called veil or velum., Due to the growth of gills and stalk the velum bursts and the two cavities colasces, with each other and a ring like remnant called annulus attached to the upper part of the stipe., , Fig.7.12. ShowingDevelopment of basidiocarp. A,B,C,D,E. Development stages of sporophore., F. Mature basidiocarp, , A mature basidiocarp consists of a fleshy cylindrical pinkish while coloured stipe, holding the umbrella like pileus. At the way of stipe an annulus a ring or collar like structure, (remains of velum) is found. Pileus has a diameter of 2-4 inches. Its upper surface is convex, light brown colored. Lower surface is concave having a large number of vertical plate like, structure called gills or lamellae. Lamellae radiate from the stipe towards the edge of pileus., Pink in colour when young but as they mature they become dark brown in colour. Each gill, is covered on both sides by a spore bearing layer, the hymenium (Fig. 7.12)., UTTARAKHAND OPEN UNIVERSITY, , Page 179
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , V.L.S. of gills shows following structure (Fig.7.13), Trama, Sub – hymenial layer, Hymenial layer, , Trama: It is the innermost or middle part of the gill consist of interwoven mass of slender, and elongated hyphae. Hyphae run parallel to each other. Hyphae of trama after attaining, certain growth bend outwards and terminates in a layer of small rounded cells forming sub –, hymenial layer., , Sub-hymenial layer on both sides have smaller pseudoparenchymatousplectenchymatous, cells., , Hymenial layer: The cells are elongated club shaped dikaryotic cells. These are of two, types. One called basidia and other is cystidia. Karyogamy takes place in mature basidium, making it diploid. The diploid nucleus undergoes meiosis resulting ito four haploid nuclei., At this stage four small outgrowth appears over the surface of the basidium called, sterigmata. The tip of each sterigmata swells. The four nuclei are pushed along with a little, of cytoplasm into these swelling due to the formation of a large vacuole in the basidium., Now the swelling on sterigmata are called basidiospores. Basidiospores are rounded ,, haploid, unicellular at first pink colour later on purple brown in colour. Thus, from each, basidium, four basidiospores are produced, the two belongs to (+) strain and the other two to, (-) strains (Fig.7.14)., , Fig.7.13. Showing Section of hymenium, , Discharge of spores takes place by water droplet method. When the basidiospores are, matured small projection called hilum appear at the junction of body of basidiospores and, strigma. A small water drop about one ourth of the size of basidiospores grows and then the, basidiospore is suddenly shot away from the sterigmacarriying the drop with it., , UTTARAKHAND OPEN UNIVERSITY, , Page 180
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.7.14. Showing Basidium with a pair of sterigmata, one bearing a basidiospore from hilum, of which a drop pf fluid has been exuded just before spore discharge. From the second, sterigma, spore has been shot off, , When the basidiospores fall on suitable substratum, germinate to form the primary, monokaryotic mycelium either or (+) strain or of (-) strains (Fig.7.15)., , Fig.7.15: Showing germination of Basidiospores, , UTTARAKHAND OPEN UNIVERSITY, , Page 181
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (i), , (ii), Fig.7.16. Showing Life cycle of Agaricuscampestris, , 7.5 DEUTROMYCOTINA, UTTARAKHAND OPEN UNIVERSITY, , Page 182
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Alternaria, 7.5.1 General account, In this, student will learn about the characteristic of Deuteromycotina with, particular reference to Alternaria., Deuteromycotina includes those fungi which reproduce only by asexual, methods producing asexual spores called conidia. That is why Deuteromycotina is, called fungi imperfectii. Their conidia are singly or in groups and are formed on, four different types of structures. These are called Synnema, Sporodochium,, Acervulus and Pycnidium., Systematic position of Alternaria is as follows:, Mycota, Eumycotina, Deuteromycotina, Moniliales, Dematiaceae, Alternaria, , 7.5.2 Habit and habitat, It is a cosmopolitan strongsaprobic and weak parasitic form genus. Some, common species are as follows:, A. solani causing Early blight of potato., A. tenuis causing black spot disease on wheat, A. Brassicae & A. brassicola both cause leaf spot of crucifers i.e. cabbage, mustard,, cauliflower etc., Some of the parasitic species cause Hay-fever and few saprobic species are common, contaminants, also occur on culture media and dead plant parts., A.solani on potato leaflets produce spots which give a blighted appearance. Spots are small, isolated scattered pale brown to dark coloured and are angular or oval in shape. There is, narrow chlorotic zone which gradually invade the normal green area of the leaflets (Fig.7.17)., , Fig.7.17: Showing early blight symptom on potato leaf and potato skin, UTTARAKHAND OPEN UNIVERSITY, , Page 183
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 7.5.3 Structure, Mycelium consists of hyphae which are light brown coloured at early stages but, latter on they become dark brown, slender, septate, profusely branched. At early stages of, growth the hyphae are intercellular latter on become intracellular within the host cells., , 7.5.4 Reproduction, The genusAlternaria also reproduce only by asexual spores called the conidia., These are produced on conidiophores. The conidiophores are straight or flexuous, short,, dark coloured. They come out of the host through stomata or through dead, damaged parts, of the host surface. There are multi septate conidia and are borne on the conidiophores not, by construction and subsequent enlargement of a terminal cell but from a bud which is, formed on that cell., , Fig.7.18: Showing stages in the development of mycelium, conidiophores and conidia of, Alternaria alternate, A. solani(G-H), A. brassicae(I)and A. brassicola(J), , Conidia are large, dark coloured, obclavate( rounded base and pointed tip), terminating into a beak like structure. Conidia are divided by septa. Septa are transverse as, well as longitudinal. Matured conidia get detached from conidiophores and are disseminated, by wind. In the presence of moisture they germinate quickly by sending 5-10 germ tubes, (Fig.7.18, 7.19)., , UTTARAKHAND OPEN UNIVERSITY, , Page 184
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.7.19: Showing conidiophores and conidia of Alternaria, , 7.6 MYCOPLASMA- GENERAL ACCOUNT, Systematic position (Frenndt, 1955), Kingdom:, Bacteria, Phylum:, Tenericutes, Class:, Mollicutes, Order:, Mycoplasmatales, Family:, Mycoplasmataceae, Genus:, Mycoplasma, Nocard and Raux French scientists in 1898 observed association of Mycoplasma with a, disease called bovine pneumonia. This is highly contagious disease. It was only in 1956 the, International Committee of Nomenclature of Bacteria placed them in a seprate class, Mollicutes on the basis of absence of a rigid cell wall. So these are bacteria like organisms, lacking cell wall and posses a three layered cellular membrane. Mycoplasma is made up of, two words:, Greek Mykes + Plasma, Fungus + Forms (Albert Bernhard Frank, 1889), , Mycoplasma (Tulian Nowak), These are also called Pleuropneumonia like organisms (PPLO) because these organisms, resembled with the causal organism of Pleuropneumonia in cattles., , Importance, Species are saprophytic or parasitic. Parasitic spp. have been reported to cause a large, number of diseases in humans and animals. Some are as follows:, M. genitalium – Pelvic inflammatory infection., M. pneumonia – primary atypical pneumonia in man., Bovine pleuro pneumonia in animals, Alfa yellow disease, UTTARAKHAND OPEN UNIVERSITY, , Page 185
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , BSCBO-101, , Papaya bunchy top disease, , Morphology and Structure:, Because they lack rigid cell wall, they do not have a definite shape. It changes from rounded, to oblong, and thus, they are called pleomorphic. These organisms are unicellular,, prokaryotic, normally non motile and have fried egg shaped colonies., , Fig.7.20: Showing structure of Mycoplasma, , They can pass through bacterial filters. Cells are delimited by a lipoproteinaceous unit, membrane which is triple layered i.e. Plasma membrane. Both DNA (base) compounds, from 23 to 36 mole percent GC (cf. L-forms)., RNA and ribosomes are present. Cells are resistant to antibiotic like penicillin. Cells, are inhibited by tetracyclines because they react on metabolic pathways. Size varies (300nm, to more) and diameter about 0.2µm. Internal structures is those of prokaryons and generally, resembles with true bacteria. Growth requirements are eg. Carbohydrates and Arginine., Metabolism substrate is fermentation. Motility is gliding or non- motile. Although they, resembles with prokaryotes but they have one feature common with Eukaryotes i.e. have, sterols lipid, cholesterol and cholesterol esters that are characteristic of animal cells and, found in mycoplasmas. These are absent in the cells of Bacteria (Fig.7.20)., , Reproduction:, Reproduction takes place by binary fission, budding or forming small spherical elementary, units within the cells. These minute bodies may form chains or filaments of minute, spheres,which are small in size. After liberation these minute bodies enlarge in size. Inside, these new elementary bodies are formed. These bodies liberate after the rupture of, membrane of large body and become free., , UTTARAKHAND OPEN UNIVERSITY, , Page 186
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 7.7 SUMMARY, 1. Puccinia (Rust) is an obligate parasitic, heteroceious polymorphic and macrocyclic, fungus., 2. Puccinia has mycelium consist of primary monokaryotic hyphae and secondary, dikaryotic hyphae., 3. Reproductive structure borne in sporangium (receptive hyphae and spermatia)., 4. Plasmogamy is by spermatization. Aecia are first binnucleate cells of the life cycle., Uredospores are one celled and teleutospores are bicelled. Karyogamy takes place in, teleutospores and meiosis in promycelium/probasidium. Basidiospores are haploid one, celled. Out of four basidiospores two are of one strain(-) and two are of (+) strain., 5. Agaricus (Mushroom) is saprobic. Species growing in well mannured lawns, on wood and, in field. *Some species are edible. Agaricusconsists of mycelium which is primary,, secondary and tertiary. Primary mycelium is monokaryotic. Tertiary mycelium forms, basidiocarps. Basidiocarps is umbrella liked structure. Sexual reproduction results in the, formation of haploid basidiospores., 6. Alternariais saprobic and pathogenic fungus. It is a common contaminants of, laboratories., 7. Mycoplasma are prokaryotic organism resembles bacteria in many characters except, few. The most striking difference is absence of cell wall., 8. They resemble eukaryotes in having sterols in cytoplasmic membranes, which stabiles, the membrane and protect the cells against the osmotic lysis. Cholesterol and cholesterol, esters characteristic of animal cell are found in mycoplasma., 9. Absence of cell wall provides resistance against enzyme and penicillin. One species, M.gallisepticum is different from other mycoplasma in many properties eg. in having, membrane bound vesicle (bleb)., 10. Reprduction is by binary fission, budding or formation of special elementary units within, the cells., , 7.8 GLOSSARY, Agaric: common name for any member of the order Agaricales(Basidiomycota); a, mushroom., Alternate host: used in reference to one of the hosts of a heteroecious rust fungus; the host, upon which stages 0 and 1 are produced., Annulus: the ring found on the stalk of certain species of mushrooms; a remnant of the, inner veil., Antibiotic: a substance produced by living organism which injuries or kills another living, organism., Basidiocarp: a fruit body that contains basidia., Basidiospores: a spore borne on the outside of a basidium, following karyogamy and, meiosis., , UTTARAKHAND OPEN UNIVERSITY, , Page 187
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Basidium: a structure bearing on its surface a definite number of basidiospores (typically, four) that are usually formed following karyogamy and meiosis., Basipetal: a chain of spores with the youngest at base or proximal end of the chain(cf., acropetal), Bipolar heterothallism: used to describe a type of sexual compatibility that is controlled by, one pair of genes., Clamp connection: a bridge like hyphal connection characteristic of the secondary, mycelium of many basidiomycota; involved in maintaining the dikaryotic condition., Coenocytic:nonseptate; referring to the fact that nuclei are present in the cytoplasm without, being separated by cross-walls, that is, the nuclei lie in a common matrix., Colony: a group of individual of same speices living in close association; in fungi, the term, usuallyrefers to many hyphae growing out of a single pointand forming a round or, globosethallus or a groupof cells that presumably are derived from a single cell., Compound oosphere : an oosphere with many functional gamete nuclei in Oomycota., Conidiogenous cell: a hyphal compartment or cell from which a conidium is formed., Conidiophore: a simple or branched hypha arising from a somatic hypha and bearing at its, tip or side one or more conidiogenous cells; previously used interchangeably with, conidiogenous cell., Conidium: a nonmotile asexual spore usually formed at the tip or side of a sporogenous, cell; in some instances a preexisting hyphal cell may be converted to a conidium., Deuteromycetes:Imperfectfungi that only reproduce asexually., Dictyospore: a pair of closely associated, sexually compatible nuclei; each may or may not, be derived from a different parent hypha or cell., Dioecious: refers to species in which the sexes are segregated in different individuals; the, use of this term is often restricted to plants., Epigean: above the ground (cf. hypogean)., Fairy ring: a ring of mushrooms produced at the limits of the underground mycelium., Frucification: any complex fungal structure that contains or bears spores; a sporocarp., Gametangial contact: a method of sexual reproduction in which two gametangia come in, contact but do not fuse; the male nucleus migrates through a pore or fertilization tube into, the female gametangium., Gametangial copulation: a method of sexual reproduction in which two gametangia or, their protoplasts fuse and give rise to a zygote that develops into a resting spore., Germ tube : the hyphal structure that first emerges from a germinating spore in most fungi;, germ tubes either develop into hyphae or, in the case of some pathogenic species, give rise, to specialized infection structures., Haustorium :an absorbing organ originating on a hypha of a parasite that penetrates the, host cell wall and invaginates the host cell plasma membrane; most often formed by obligate, parasites., Heterothallic:self-sterile (self-incompatible) individuals requiring the union of two, compatible thalli (of different mating types) for sexual reproduction; obligate outcrossing, (cf. homothallic)., Heterothallism: the condition exemplified by heterothallic species., Host: a living organism harboring a symbiont (usually in a parasite connotation)., UTTARAKHAND OPEN UNIVERSITY, , Page 188
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Hyaline: transparent or translucent., Hymenomycetes: general term used to refer to Basidiomycotatht produce their basidia in, adefinite layer or hymenium., Hyperplasia: excessive multiplication of cells, abnormal rate of cell division., Hypertrophy: excessive enlargement of cells., Hypha:the unit of structure of most fungi; a tubular filament., Hypogean: growing below ground(cf. epigean)., Imperfect fungi: see deuteromycetes., Imperfect state: the asexual (usually conidial) state of afungus; also known as anamorph in, a life cycle with a sexual state (telelomorph) (cf. perfect state)., Indirect germination: in Oomycota, germination of sporangia by zoospores; in, Ascomycota and Basidiomycota, germination of spore to form a secondary spore without, germ tube formation., Karyogamy: the fusion of two nuclei (cf. plasmogamy)., Macrocyclic: a rust fungus that typically exhibits all five stages of the rust life cycle., Macrocyclicconidiation: formation of conidia following the development of a mycelium, from a germinated spore., Medium: substratum of a balanced chemical composition employed in the laboratory for, growing microorganisms; media may be used in the liquid state or solidified with agar,, gelatin, or other solidifying agents., Monokaryotic: condition of having a single nucleus in each hyphal compartment (cf., homokaryotic; dikaryotic)., Muriform: term used to describe a spore with both transverse and longitudinal septa, as in a, dictyospore., Mushroom: a fleshy, sometimes tough, umbrella like basidiocarp of certain Basidiomycota., Mycelium: mass of hyphae constituting the body(thallus) of a fungus., Mycology: the study of fungi., Oidium: a thin walled, free, hyphal dead cellderived from the fragmentation of somatic, hypha into its component cells or from an oidiophore; it behaves as a spore or as a, spermatium; normally used in reference to such cells produced by certain Basidiomycota., Oidization: the union of an oidium with a somatic hypha, resulting in the dikaryotization of, the latter., Oogamous: refers to a type of fertilization in which two heterogametangia come in contact,, and the contents of one flow into the other through pore or tube., Oogonium: a female gametangium containing one or more eggs., Ooplast: membrane bound cellular incision in the oospore of some of Oomycota., Oosphere: a large naked, nonmotile, female gamete., Oospore: a thick walled spore that develops from an oosphere through either fertilization or, parthenogenesis., Parasite: an organism that lives at the expense of another, usually invading it and causing, disease., Perithecium: a closed ascocarp with a pore at the top, a true ostiole, and a wall of its own., Plasmogamy: the fusion of two protoplasts (cf. karyogamy)., Primary appendage: an outgrowth that develops from the ascospore cell in Laboulbeniales., UTTARAKHAND OPEN UNIVERSITY, , Page 189
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Primary septum: a septum formed in association with a nuclear division; laid down, between daughter nuclei., Promycelium: a germ tube issuing from the teliospore in which meiosis takes place an that, bears basidiospores; technically, the metabasidium., Pycnidiospore : a conidium borne in a pycnidium., Pycnidium: a hollow conidioma lined with conidiophores., Pycniospores: another designation for the spermatium of the rust fungi., Pycnium : another designation for the spermogonium of the rust fungi., Receptive hypha: the structure with which a rust spermatium fuses., Saprobe: an organism that utilizes dead organic matter for food., Secondary heterothallism: apparent homothallism that actually involves the presence of, two compatable mating types in a single spore, also known as amphithalism., Secondary zoospore: kidney-shaped zoospore produced in Oomycota; the flagella are, inserted laterally on the spore (cf. primary zoospore)., Self-compatible: self-fertile; refers to a thallus that reproduces sexually without outcrossing., Self-incompatible:self sterile; refers to a thallus that cannot reproduce sexually without, outcrossing., Septal pore cap: see dolipore septum., Septate : with more or less regularly occurring cross-walls., Septum: a cross-wall in a hypha that develops centripetally., Somatic: refers to the assimilative phase in fungi; a structure or function as distinguished, from the reproductive; also referred to as vegetative., Somatogamy: fusion of somatic cells during plasmogamy., Species: a taxonomic rank; a group of closely related individuals resembling one another in, certain inherited characteristics;it is designated by a binomial consisting of the generic name, and the specific epithet., Spermatiopores: a specialized hypha that produces spermatia., Spermatium : a nonmotile, uninucleate, sporelike male structure that empties its contents, into a receptive female structure during plasmogamy; spermatia are regarded variously as, gametes or gametangia., Spermogonium : a structure resembling a pycnidium and containing minute, rod shaped, or, oval spore like bodies that in some cases have proved to be functional spermatia., Sporangiophore: a specialized hypha that bears a sporangium., Sporangiospore : a spore borne wihin a sporangium., Sporangium: a saclike structure, the entire protoplasmic contents of which become, converted into an indefinite number of spores., Spore:a minute propagative unit functioning as a seed, but differing from it in that a spore, does not contain a preformed embryo., Stipe : the stalk of a stipitatebasidiocarp or ascocarp., Substrate: any substance or material from which a fungus can obtain nutrients., Trama: the fungal tissue composing the pileus or bearing the hymenium of some, basidiomycota., Urediniospore:a binucleate, repeating spore of Uredinals or rust fungi., , UTTARAKHAND OPEN UNIVERSITY, , Page 190
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 7. Basidiocarp of Agaricus is like:, (i) Fan, (iii) Stick, , BSCBO-101, , (ii) Umbrella, (iv) Ball, , 8. Which layer in a V.L.S. of gill of Agaricusis fertile:, (i) Hymenial, (ii) Sub-hymenial, (iii) Excip…, (iv) None of the above, 9. Out of five types of spores of P. graminis which is dikaryotic and bicelled:, (i) Uredospore, (ii) Teleutospore, (iii) Aeciospore, (iv) Basidiospore, 7.9.2: Fill in the blanks:, 1.……………………..disease caused by different species of Puccinia., 2. At the ………..stage of life cycle of P. graminis in which karyogamy take place., 3. Agaricus is also called…………, 4. Conidia of Alternaria are ……………, 5. PPLO stand for……………, 6. Mycoplasma differs from prokaryotes in…………, 7. List some disease caused by Mycoplasma………………, , Answers Keys: 7.9.1:, 1. (ii), 2. (iv), 3. (iv), 4. (ii), 5. (ii), 6. (iii), 7. (ii), 8. (i), 9. (ii), , Answers Keys: 7.9.2:, 1. Black rust, yellow rust, stripe rust, 2. Telial, 3.Mushroom, 4.Multicellular,, 5.Pleuropneumonia like organisms, 6. Usually requires sterol for growth 7. Alfaalfa,, Witches broom, Papaya bunchy top, Clover Phyllody, Grassy Shoot of Rice etc., , 7.10 REFERENCES, , , , , , , Anisworth, G.C. 1964. A general purpose classification of fungi Bibl. Syst. Mycol. No. 1:, 1-4., Anisworth, G.C. 1973. Introduction and keys to higher Taxa. In: The Fungi. An, Advanced Treatise.( G. C. Anisworth, F. K. Sparrow and A. S. Sussman,, eds.).International, Oxon, U.K., Hawkswarth , D.L. et al. (1995) Aniswarth and Bisby‘ Dictionary of Fungi CAB, International, Oxon, U.K., Kirk, P.M. etal. 2008 Anisworth and Bisby‖s Dictionary of the Fungi (10th ed.) CAB, International, Oxon, U.K., , UTTARAKHAND OPEN UNIVERSITY, , Page 192
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , , , BSCBO-101, , Kran C.J, Gardnar M.W 1973 Etmyology of the term Mycoplasm Int. J. Syst. Bac. 23 (1), 62-64., Larsen, Bryan, Hwang, Joseph (2010) Mycoplasma, Ureplasm and advance pregnancy, out comes. Infection disease in obstetrics and Gynecology 2010: 1-7., Lis, R, Rowhani, Rahaban and Manhart, L.E 2015.Mycoplasma genitalium infection and, female reproduction tract disease. A meta analysis clinical infection diseases 61(3): 418426., Ryan K J and Rany C G 2004 Sherris Medical Microbiology 4th ed. McGraw Hill. 409-12, ISBN 0-8 365 – 8529-9, , 7.11 SUGGESTED READINGS, , , , , , , , , , , , , , , , , , , , , Ajello, l. d. ET AL. 1976. The Zygomycetessaksenavasiformis as a pathogen of humans, with a critical review of the etiology of zygomycotina. Mycologia. 68: 52-61., Alexopoulos C.J., Mims, C.W. and Blakwell, M. 1996. Introducting Mycology 4 th ed., John Wiley, N.Y., Alexopoulous C.J. 1962 Introductary Mycology 2nd ed. John Willey and Nysans., Barnett, H. L. 1955 Illustrated genera of Imperfect fungi. Burgers Publ. Co. Minneapolis., Bessey, E.A. 1942. Some problems in Fungus Phylogeny., Bigrami, K.S and Dube, H.C.1976 A text book of modern Plant Pathology, Vikas, Publishing House pvt.Lmtd. New Delhi., Butler, A.H.R. 1909-1950 Researches in fungi vols. I-VII, Londan., Cotter, P.U. 1960. Fertilization of pycnia with uredospores and aceiospores in, Pucciniagraminis. Phytopath. 50:567- 568., Daya, R and Raizada, B.B.S 1998-99 Introduction to Fungi Vishal Publications: India., Dube, H.C. 2013. An Introduction to Fungi 4th ed. Scientific Publishers (India)., Eaton, M. D. 1965. Pleuroneumonia like organisms and related forms. Annual Rev., Misobeal. 19: 379-406., Ingold, C.T. 1967. The Biology of Fungi 2nd ed. Hutchinson, London., Kendrick, W. B. and Carmichael J.W. 1973. Hyphomycetes. In: THE Fungi : An, advanced Treatise vol IV A ( G.C. Aniswarth, F.K.Sparrow and A.S. Sussman Eds.), pp.325-509 Academic Press, N. Y. and London., Klieneberger, Nobel,, E., 1962:, Pleuroneumonia, like, organisms(PPLO),, Mycoplasmataceae. Academic PressN.Y., Lindergen. CC.1949: The Yeast cell its genetics and cytology. Educationally Publishers,, USA., Mehta, K.C 1931. Annual recurrence of rust on wheat and barley in the plains of India., Indian J. Agric. Sci. 1:297-301., Moore, R.T. 1964 Fine structure of Mycota. 12. Karyochorosis somatic nuclear division, in CandycepsmilivarisZ elforsch. 63: 221-237., Pandey, S.N. and P.S. Trivedi. A Text Book of Botany Vol. I. 10th revised ed. 1994., Vikas Publishing House Pvt. Ltd. New Delhi., , UTTARAKHAND OPEN UNIVERSITY, , Page 193
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , , , , , BSCBO-101, , Raper, J. R. 1954. Life cycles, sexuality and sexual mechanism in fungi. In: sex in, microorganism ( D.H Wenrich, I.F. Lewis and J. R. Raper eds.). Ama. Assoc. Adv. Sci. 3:, 565- 589., Razin, S. 1969. structure and function in Mycoplasm. Annual Rev. Microbiol. 23 :155171., Smith, G. M. 1955. Cryptogamic Botany. Vol. I. McGraw. Hill Book Co. NY., Subranium, C.V. 1962. A classification of the HyphomycetesCurr. Sci. 31 : 409-411., Tandon, R.N. and Srivastava, J.p. 1958. Studies on species characteristics of, Alternariatenius . Proc. Nact. Acad. Sci. 28:155-171., Waksman, S.A. 1917. Is there any fungus flora of the soil? Soil Sci. 3:565-589., , 7.12 TERMINAL QUESTIONS, 1. How many stages are there in the life cycle of Pucciniagraminis. Give their names and, host on which these stage are found., 2. Describe the life cycle of Pucciniagraminis with the help of figures only., 3. Differentiate between uredospores and teleutospores., 4. Draw well labeled diagrams of section passing through uredia, telia, aecia and pycnidia., 5. What are fairy rings?, 6. Draw morphology of basidiocarp of Agaricus., 7. Draw V.L.S. of gill of Agaricus., 8. What is button stage in the life cycle of Agaricus., 9. Name few species of Alternaria., 10. Write asexual reproduction in Alternaria., 11. Give general account of Mycoplasma., , UTTARAKHAND OPEN UNIVERSITY, , Page 194
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-8-OCCURRENCE, GENERAL STRUCTURE,, NUTRITION, REPRODUCTION, ECONOMIC AND, ECOLOGICAL IMPORTANCE OF LICHENS, 8.1-Objectives, 8.2-Introduction, 8.3-Occurrence, 8.4-General structure, 8.5-Nutrition, 8.6-Reproduction, 8.7-Economic and ecological importance, 8.8- Summary, 8.9- Glossary, 8.10- Self assessment question, 8.11-References, 8.12-Suggested Readings, 8.13-Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 195
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 8.1-OBJECTIVES, After reading this unit student will be able:, , , , , , , To know about lichens and their occurrence., To learn the basic growth forms of lichens: crustose (crusty), fruticose(shrubby), and, foliose (leafy)., To know general parts of the lichen., To understand the methods of reproduction in lichens., To study the economic importance of lichens., , 8.2-INTRODUCTION, A lichen seems like a single organism, but actually it is a combination of two plants an alga, and a fungus which live together in a symbiotic relationship. The algal component in the, lichen is known as phycobiont and fungal component is called as mycobiant. The 90% part of, the thallus (body of the lichen) is produced by the mycobiant. In a lichen, the mycobiant, produces a thallus and provides colour, shape and structure to the lichen with little, contribution from algae. This fungal component mostly belongs to the group Ascomycetes,, Deuteromycetes, or Basiodiomycetes of fungi. 95% of lichen species belong to the, Ascomycetes. While 3% is represented by Basidiomycetes and 2% by Deuteromycetes. The, Phycobiont (algal part) belong to the family Chlorophyceae or Myxophyceae. The alga, supplies nutrients by photosynthesis, while the fungus protects the alga from excessive Sun, rays and supplies water by absorbing water vapor from the air. It may be a type of, relationship called a ‗symbiosis‘ where both partners get benefitted., , History of Lichens: The word Lichen appeared 1600, and was drawn from the Greek, ‗leikhen‘, meaning ‗what eats around itself‘. The term ‗Lichen‘ and this group of plants were, introduced by Theophrastus, the father of botany. Those who studied lichen are called, lichenologist. In 1867 Swiss botanist Simon Schwendener first proposed the theory of the, duality of the lichen thallus. According to his theory, alga and fungus share a relationship as, helotism where the Alga was slave providing nutrient to fungal master. In 1887 De-Bary used, the term Symbiosis for association of lichen. Schwendener‘s dual theory of lichens has been, accepted by every one for which experimental proof has been obtained., , 8.3-OCCURRENCE, Lichens are very common and widely distributed from the arctic to Antarctic regions of the, world. They can survive in extremes of hot and cold weather. They are mostly xerophytic in, nature and can endure long periods of drought, tough conditions of deserts and frozen soil of, the artic region. Lichens may become dormant in unfavourable environmental conditions for, some time and then they become metabolically active again on return of more friendly, conditions. These plants can be found most frequently on stems, bark and trunks of trees,, UTTARAKHAND OPEN UNIVERSITY, , Page 196
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , rocks, soil, lands, stones etc. Lichens do not have roots, thus they can grow in areas where no, other vegetation is possible such as concrete, sand, stable rock surfaces etc. A few are, unattached and blow about freely. Lichens are favoured by sufficient humidity, sunlight, still, conditions and clear air. Most of the lichens generally depend on atmospheric sources for, nutrition in feeding itself through photosynthesis in the algal cells., , 8.4-GENERAL STRUCTURE, Classification of lichen:, (A)Lichens are classified on the basis of the nature of fungal part:, (i) Ascolichens: In this, the fungal component belongs to Ascomycetes. Such lichens are, divided into two sub-groups(a) Gymnocarpeae: In which fruiting body (i.e. ascocarp) is apothecium. e.g.- Parmelia, (b) Pyrenocarpeae: In which the ascocarp is Perithicium type. e.g.- Dermatocarpon, (ii) Basidiolichens: in this, fungal component belongs to basidiomycetes. e.g. Dictonema,, Corella., , (B)Wall Roth classified lichen into two types on the basis of Algal component:, (i), , (ii), , Homiomerous:In this, the algal component is distributed throughout the structure, and the fungal part grows outside the thallus as a thin protective layer. e.g.Collema, Heteromerous: The algal component in a heteromerous is confined to a specific, region. The heteromerous thallus can be differentiated into four distinct layers,, three of which are formed by the fungus and one by the alga. e.g. Parmelia,, Xanthoria., , (C) Lichens are classified on the basis of Growth forms:, (i) Crustose: These lichens have a flattened thallus, resembling crusts, generally grown on, rocks or occasionally on the bark of trees holding tightly to their substrates and it is difficult, to remove them without crumbling away. e.g.- Haematomma lecanora, Graphis, Lacidia etc., (ii) Foliose: These lichens have a flat, expanded, leaf like thallus which spread out in a, horizontal layer over the surface. They are attached by root-like threads and can be easily, dismantled without damaging the substrates. e.g. - Physcia, Parmelia, Gyrophora etc., (iii) Fruticose: These lichens have a thallus that is branched and bushy and can hang from, the substrate. It may be erect or pendant. They can be removed from the surface by hand., e.g.-Cladonia rangiferina, Usnea barbata (Fig.8.1)., , UTTARAKHAND OPEN UNIVERSITY, , Page 197
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.8.1- Lichens, , Internal Structure of Lichens:, (a) Upper cortex: It forms the upper most layer which is generally thick and protective, in nature and consists of more or less vertical fungal hyphae. The fungal hyphae are, compactly interwoven without any intercellular spaces to produce a tissue-like layer, which is known as Plectenchyma or Pseudoparenchyma., (b) Algal Zone: This zone lies beneath the upper cortex. This zone generally consists of, blue-green algae. In this layer algal cells intermingled with loosely interwoven fungal, hyphae. The algal zone is the photosynthetic region of the lichen thallus and was, known as gonidia., (c) Medulla: It is the central core of the thallus and is composed of loosely arranged, fungal hyphae with intercellular spaces. It works as a water reservoir. Usually, the, wall of the fungal hyphae is thick and strong. The hyphae run in all directions., (d) Lower cortex: The lower cortex is below medulla. It is formed by fungal component, and made up of compact hyphae. They may be parallel to perpendicular to the surface, of the thallus (Fig.8.2)., , UTTARAKHAND OPEN UNIVERSITY, , Page 198
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.8.2: Internal structure of Lichen, , Anatomy of the lichen thallus:, The vegetative structures which are associated with the lichen thallus are:, (i) Breathing Pores: These are localized openings which develop in the upper cortex., The breathing pores serve for aeration and helps in respiration., (ii) Cyphellae: The cup-like white spots present on the lower cortex in some foliose, lichens are known as cyphellae. These cup-like breaks are formed of loosely arranged, medullarly fungal hyphae. Their function is aeration., (iii)Cephalodia: Cephalodia are small, dark-coloured, hard, gall-like swellings found in, some species of lichens that contain cyanobacterial symbionts, the cyanobacteria may, be held on the upper or lower surface of lichen thalli. The cephalodium consist of, fungal hyphae and a few algal components., (iv) Isidia: A coralloid out growths on the surface of a lichen thallus consisting of both, fungal hyphae and algal cells. The main functions of isidia is supposed to increase the, photosynthetic surface of the lichen thallus. In terms of structure, isidia may vary in, form in different lichen species as- cylindrical, warty, cigar shaped, clavate (clubshaped), scale-shaped, coralloid (coral-shaped), rod-shaped etc (Fig.8.3, 8.4)., , Colour: Lichens show many colours. It can be red, oranges, yellow, green, white, grey etc., The colours vary due to presence or absence of special pigments.In the absence of special, pigments, lichens are generally bright green to olive gray when it is wet and grey or grayishgreen to brown when dry. This is because the cortex becomes more transparent and the, underlying green photobiont layer becomes visible. Colours vary due to genetics, age and on, the angle of exposure to light. Most widespread special pigments such as pale yellow usnic, acid, give lichens a variety of colours as yellow, red, and orange., , UTTARAKHAND OPEN UNIVERSITY, , Page 199
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 8.5-NUTRITION, Lichens get mineral nutrients from whatever they are growing upon. The fungus uses the, hyphae to absorb food from its surroundings. The fungus gets benefits from the symbiotic, relation because algae or cyanobacteria produce food by turning sunlight into energy through, photosynthesis, water and minerals in their environment. Cyanobacteria can make amino, acids directly from the nitrogen gas in the atmosphere. Fog, dews, play an important role in, atmospheric nutrition of lichens. It has been observed that a dry lichen thallus can take in as, much as 3-35 times their weight in water., , 8.6-REPRODUCTION, The lichens reproduce by following methods:, , Vegetative Reproduction: Lichens may reproduce vegetatively by several methods., (i) Fragmentation: A fragment broken off from a lichen thallus may grow into a new, thallus. On maturity or accidental breakage the older portions of the thalli of lichens, divide into pieces and each piece develops into a new plant. This is a means of, vegetative propagation. The new thallus being genetically identical to the thallus from, which the fragement came., (ii) Isidia: Isidia are tiny, simple, branched, spiny, elongated out growths from the, thallus that break off or scattered by animals, wind and rain to new locations. Each, isidium is composed of a few algal cells surrounded by fungal cells. Each isidium, grows into a new lichen thallus under favourable conditions., (iii)Soredia: These are minute, powdery granules or bud-like out growth present on the, upper surface or edges of the thalli of many species of lichens. At times the soredia, form a grayish layer of dusty mass which is known as the soredial dust. Each, soredium consisting of one or a few algal cells surrounded by fungal hyphae. Soredia, can be dispersed easily by wind and contain everything needed to produce new thalli., , Soredia, , Isidia, , Fig.8.3: Vegetative structure, , UTTARAKHAND OPEN UNIVERSITY, , Page 200
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig. 8.4: Isidia (Peltigera sp.) V.S.thallus, , Asexual Reproduction: Certain lichen produces large number of small non-motile sporelike structures, pycnidiospores. They are formed within conical, flask- shaped cavities known, as pycnidia. The pycnidia are found sunken on the upper surface of certain lichens and each, pycnidium opens to the exterior by a small pore called an ostiole. In certain species of, lichens, the pycnidiospores are capable of germination. Each produces a fungal hyphae and, when it comes in contact with suitable algal cell, it develops into a new lichen thallus., , Sexual Reproduction: Only the fungal partner of the association reproduces sexually. The, male reproductive organ is called spermogonium and the female is called as carpogonium or, Ascogonium., i) Spermogonia: The spermogonia develop in flask-shaped cavities on the upper surface of, the thallus. It opens to the exterior by small pore, an ostiole. A number of hyphae develop, from the walls of the cavity. Few of them are sterile and others are fertile. The fertile ones, produce the non-motile male cells called spermatia. These non-motile cells develop, continuously from the tips of the fertile branches. The spermatia are set free in a slimy mass, through ostiole., ii) Carpogonia: The carpogonium develops from hypha deep in the algal layer. It consists, of two portions, the upper straight portion which is known as trichogyne and the lower coiled, portion which is called ascogonium (oogonium). It is multicellular and the cells are, uninucleate or multinucleate in some species. The basal cell of the ascogonium is fertile., , Fertilization: A spore called conidium is released from a pycnidia structure. Pycinidia are, flask-like structures embedded in the thallus of the lichen. Conidia can act as ―spermatia‖ in, sexual reproduction of the lichen. The spermatia are functional male gametes. The, spermatium spore finds its way to a tiny thread (trichogyne) on a surface of lichen and, attaches itself. The conidia and the trichogyne both are haploid. The growing trichogyne, comes in contact with spermatia. The intervening walls between the spermatium and the, trichogyne dissolve at the point of contact. The male nucleus gradually passes downward to, the oogonium, where it fuses with the female nucleus. The actual migration of the male, UTTARAKHAND OPEN UNIVERSITY, , Page 201
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , nuclei down the trichogyne has not yet been observed, but it is assumed. Fused cell produces, ascogenous hyphae within which develop 8 ascospores and asci. The hynenium is made up of, Asci and Paraphysis. The fruiting body may be either apothericia. e.g. -Parmelia and Physcia, or Perithericia e.g.-Peltigera., In lichens, fruiting bodies are of following two types:, (i) Apothecia: Apothecia are variable in shape but commonly wide, open, saucershaped or cup shaped fruit body. Sometimes these may be plate-like and rarely it has, an elaborate form. The structure of the apothecium mainly consists of three partsHymenium (upper convex surface), Hyopothecium, and Excipulum. The asci are, present in the hymenium layer. The hymenium, composed of sac-like asci and sterile,, hair-like fungal hypae known as Paraphyses. Asci and Paraphyses form a thin inner, lining, which is called as hymenial layer. Each ascus contains eight ascospores. From, outside apothecium generally seen to consist of two parts, the margin and the disc., Apothecia have two main types of margin: a) A proper margin consisting of fungal, hyphae only; generally, the proper margin is sometimes conspicuous and of different, colour as compare to the disc, but more often is similar in colour to the disc, different, from the thallus.The outer margin of an apothecium is called the exciple. The, lecideine type of apothecium has only a proper margin where the exciple forms the, underside and outer layer of the apothecium, extending up to the rim, where it forms, the proper margin consisting of fungal hyphae only. A thalline margin, which includes, photobionts, different from the disc (with several exceptions e.g., in Caloplaca)., When the excile has a color similar to colored thallus tissue the apothecium is called, lecanorine. In lecanorine apothecia, the thallus tissue s extend up the outside of the, apothecium to form the exciple and rim. Generally this thalline margin retains the, colour of the thallus (Fig.8.5)., , Fig.8.5: Apothecium, , (ii) Perithecia: Perithecia are usually flask-shaped fruiting bodies containing the asci, immersed in the lichen thallus tissue. Here the spore bearing body is much smaller in, size than the apothecia and appear like black dots on the lichen surface. At maturity, a, small opening at the top which is called an ―ostiole‖, allows the ascospores to escape., Perithecium producing lichens are called Pyrenocarpic e.g., Margacea (Fig.8.5)., , UTTARAKHAND OPEN UNIVERSITY, , Page 202
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.8.6: Perithecium, , Basidiolichen: A very small number of lichens have the fungal part which belongs to the, Basidiomycetes with fruiting bodies, basidiocarps. Basidiocarp is a sexual fruiting body, produced by a member of Basidiomycota, and could take any of a diversity of shapes a clublike, sheet-like, bracket-like etc. The club-shaped basidium carries sexual spores called, basidiospores. The lower surface of the thallus bears sub-hymenium. Each basidium produce, four spores on the tips of minute stalks called Sterigmata., , 8.7-ECONOMIC AND ECOLOGICAL IMPORTANCE, Economic importance: Lichens are very important economically. Following are some, examples of there importance:, 1- Medicinal Use: A few species of lichens have been used in folk medicines for, centuries as a cure for diarrhea, fever, jaundice, skin diseases, epilepsy etc. It is, known that acids from various lichen can be useful in killing bacteria. Labaria, pulmonariais used in asthma and lung diseases, Xanthoria parietina for jaundice,, Peltigera canina for dog bite. Usnic acid secreted from Usnea barbata, along with, streptomycin is effective in tuberculosis. Lichen mass produces mucilaginous, substance obtained from Cetraria islandica is used as laxative. Cladonia pyxidata is, useful in whooping cough. Researches are yet to be conducted on many other, medicinal benefits of lichens.Peltigera canina was used as medicine for hydrophobia, in ancient time. Parmelia saxatilis is used to cure epilepsy. The Usnea and Evernia, furfuraceaare used as astringents., 2- Dyeing agent: Some lichens are useful as a natural source of dyes. The fungal, components of certain species of lichens produce coloured pigments specially the red,, brown, orange etc which can be extracted by boiling and used to dye fabrics and, wood. Many lichens such as Pocelia tinctoria gives purple dyes which is used for, centuries. Orchil is a blue dye obtained from Cetraria icelandica and Lecanora, sp.which is used to dye wollen and silken clothes. Litmus is obtained from Rocella, UTTARAKHAND OPEN UNIVERSITY, , Page 203
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 3-, , 4-, , 5-, , 6-, , BSCBO-101, , montaignei which is a commonly used dye in chemical laboratories as an acid-base, indicator prior to the invention of the pH meter., Food value: Certainspecies of lichens are consumed as food because they contain, lichenin, a carbohydrate. Some lichens like Cetraria islandica,Umbillcaria, lecnora, used are as food by human beings. Cetraria islandicais used as food by Eskimos and, others. A species of Parmelia popularly known as rock flower (called as ―rathapu‖ in, telugu and ―kallu huvu‖ in kannada) is used in curry preparation and is famous for its, delicacy. It is prized as food in Southern India. Evernia prunastri was used, byEgyptians as baking powder. Umbillicaria has been used as food in eastern Siberia., Lecanora esculenta, commonly called Manna lichen is used in desert tribes of Asia, minor., As Fodder: Lichens is important for some species of animals and small insects like, snails, mites, caterpillar etc as source of food. Fruticose Lichen Cladonia rangiferina, commonly known as Reindeer grass is used as food for horses and other animals. The, other common used species for animals as fodder are Labaria pulmonaria,Ramalina, fastigiata,Ramalina fraxinea etc. Many lichens are consumed as food for insects and, their larvae., Chemical Uses: Lichen is useful in the brewing, distilling and tanning. Some Lichen, species contain tannis and used in leather tanning industry. The lung wort lichen is, used in tanning and brewing., Perfumes: Sweet-scented thalli of some lichens are used in making perfumes, scents,, dhup, hawan samagris etc. It can retain the power of retaining the odor it is used. A, lichen which is popularly known as an oak moss is used in perfumes as a fixative in, Southern Europe. It is reported that some lichens like Ramalina and Evernia have, perfumed volatile oils, which is used in manufacture of comestics., , Harmful effects of Lichens:, 1- Lichens may have adverse effects on plants. Small fruit trees, Sandal wood trees,, small shrubs densely covered with lichens could be damaged. Many epiphytic lichens, can have harmful effects on the host plant., 2- A very few lichens are poisonous. These lichens are known to contain vulpinic acid, and usnic acid, e.g. vulpicida and Letharia. These lichens are yellow due to high, concentrations of bright yellow toxin vulpinic acid. The wolf lichen (Letharia, vulpine) got its name because it was used in Europe to poison wolves. So many lichen, which is yellow in colour may have possibility to be poisonous., 3- In dry season sometimes long threads of pendant lichens as Usnea barbata help in, spreading of forest fire., , Ecological importance, Lichen is regarded as the ―Pioneers of vegetation‖. They are capable of colonizing bare rocks., These plants play very important role in the ecological formation of soil. The organic acids, secreted by lichens gradually dissolve and disintegrate the rocks into soil particles over which, they grow. Mosses are the successors of the crustaceous rocks. When the lichens die and, UTTARAKHAND OPEN UNIVERSITY, , Page 204
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , decay they contribute organic matter to the soil, improve the soil fertility so that other plants, can grow on it. Having root-like structure lichens can anchor themselves to the soil. When, there is occasional rainfall, comes the shower of rain is absorbed by the lichen thalli and often, slow down the flow of water. It works as a barrier between the intense down pours and the, soil. Lichens can enrich the soil by trapping water to support a active life over long dry spells., , Lichen as Bio-indicators or pollution indicators: Lichens are able to survive in, extreme climates but they are very sensitive to air pollution. Fruticose lichen is the most, vulnerable and Crustose is the least vulnerable lichen type to air pollution. Because lichens, are pollution- sensitive so they can provide the valuable information about the environment., Lichens absorb everything from the air, including chemicals like carbon, sulfur, heavy metals, into their thallus. Environmental scientists can extract the toxins from lichens and monitor the, intensity of air pollution. Presence of lichens in abundance in a particular area is a indicator, of non-polluted environment of the area whereas the declined growth of lichen at a site is an, early warning sign of air pollution., , A Source of Nitrogen: Nitrogen is a nutrient which is important for living organisms., Some lichens are able to convert nitrogen in the air into nitrates and then secrete it into the, soil. When it rains, nitrate is secreted into the soil and it can be useful for plants., , 8.8- SUMMARY, Lichens are the combination of two organisms, an alga and a fungus, living together in, symbiotic association. Fungi provide the body of organism while the algae or cynobacteria, provide the food. The lichen thalli are usually of three types- Fruticose, foliose and crustose., Internally the thallus consists of four regions, the upper cortex, the lower cortex, the algal, layer and the medulla. Lichens reproduce by the three methods- sexual, asexual and, vegetative reproduction. Most of the lichens depend on atmospheric sources for nutrition., These plants have had a variety of uses over the years. They are of considerable ecological, and economical importance and are useful in soil formation, habitat for other organisms,, bioindicators for pollution, a source of nitrogen, useful in making perfumes, medicines, dyes,, and important food source., , 8.9- GLOSSARY, Apothecium: A disc-shaped structure that contains the asci, especially in lichens, a type of, ascocarp., Ascocarp: mature fruiting body of an ascomycetous fungus., Ascospore: A meiospore borne in an ascus., Ascus: The sac or bag-like structure in which ascospores are formed., Conidium: An asexual fungal spore., Cynobacteria: blue-green algae., Filamentous: Stringy or matted hair like., UTTARAKHAND OPEN UNIVERSITY, , Page 205
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Gelatinous: Jelly like., Hyphae: Fungal filaments collectively called hyphae which form a thallus., Leprose: Powdery., Mycobiant: The fungal partner in a lichen., Perithecium: A flask shaped sexual reproductive structure that produces spores., Phycobiont: algal partner in a lichen., Pycnidia: Flask-shaped structures which produce conidia., Rhizines: root-like fungal structures is termed rhizines or rhizinae which bind the thallus to, its Substrate., Symbiotic: Where both the partners get the mutual benefit by living together., , 8.10- SELF ASSESSMENT QUESTION, 8.10.1: Multiple choices Questions1) The condition in which two different organismsliving together and get the mutual benefit, is known as:, (a) Parasitic, (b) Heterotrophic, (c) Symbiotic, (d) Saprophytic, 2) Generally each ascus contains:, (a) 16 ascospores, (c) 2 ascospores, , (b) 4 ascospores, (d) 8 ascospores, , 3) Which of the lichen is called as the ―reindeer moss‖:, (a) Peltigera canina, (b) Evernia, (c) Cetraria islandica, (d) Cladonia rengiferina, 4) The female reproductive organ in lichens is called:, (a) Carpogonium, (b) Paraphysis, (c) Spermagonium, (d) Trichogyne, 5) Lichens are described as indicators of:, (a) Water pollution, (c) Air pollution, , (b) Xerophytic succession, (d) None, , 6) Vegetative reproduction in lichen takes place by:, (a) Fragmentation, (b) Soredia, (c) Isidia, (d) All of these, 7) In sexual reproduction, the fruiting body formed is called:, (a) Perithecium, (b) apothecium, (c)both a and b, (d) None, , UTTARAKHAND OPEN UNIVERSITY, , Page 206
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , 8) The study of Lichen is called:, (a) Lichology, (c) Lichenology, , BSCBO-101, , (b) Mycology, (d) None of these, , 9) Sexual reproduction in lichens is carried out by:, (a) Fungal part, (b) Algae part, (c) Both a and b, (d) None, 10) Litmus is obtained from:, (a) Usnea, (b) Cladonia, (c) Roccella, (d) Peltigera, ANSWERS KEY: (A): 1- (c), 2-(d), 3-(d), 4-(a), 5-(c), 6-(d), 7-(c), 8-(c), 9-(a), 10-(c), , 8.11-REFERENCES, , , , , , A Text Book of Boatny Vol.-II, 2013, Dr. K.A. Siddiqui, Kitab Mahal, Allahabad., Botany for Degree Students, 1982, B.R.Vashishta, , S.Chand and Company, New Delhi., College Botany, Vol.-I, 2013, Dr.S.Sundararajan, Himalaya Publishing House., HTTP://WWW.PLANTSCIENCE4U.COM, , 8.12-SUGGESTED READINGS, , , , , , A Text Book of Boatny Vol.-II, 2013, Dr. K.A. Siddiqui, Kitab Mahal, Allahabad., Botany for Degree Students, 1982, B.R.Vashishta, , S.Chand and Company, New Delhi., College Botany, Vol.-I, 2013, Dr.S.Sundararajan, Himalaya Publishing House., Linecology of India by D.D. Awasthi., , 8.13-TERMINAL QUESTIONS, Q.1-Write short notes ona) Structure of Lichens, b) Classification of Lichens, Q.2- What is Lichen? Describe in detail the internal structure of lichen., Q.3 Discuss the reproduction of Lichen in detail., Q.4 Describe the economic and ecological importance of Lichen., Q.5 Discuss lichen ‗as a pollution indicator‘., , UTTARAKHAND OPEN UNIVERSITY, , Page 207
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , BLOCK 3 – PLANT PATHOLOGY, , UTTARAKHAND OPEN UNIVERSITY, , Page 208
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-9-INFECTION, DISEASE RESISTANCE AND, GENERAL SYMPTOMS, 9.1 – Objectives, 9.2 – Introduction, 9.3 – Infection, 9.4 – Disease Resistance, 9.5 – General Symptoms, 9.6 – Summary, 9.7 – Glossary, 9.8 – Self Assessment Question, 9.9 – References, 9.10- Suggested Reading, 9.11 – Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 209
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 9.1 OBJECTIVES, After reading this unit student will be able:, , , To study the living, nonliving and environmental causes of disease and disorders, inplants., , , , To study the mechanisms of disease development by pathogens., , , , To study the interaction between the plant and thepathogen in relation to the overall, environment., , , , To develop systems of management of the disease and reducing the losses caused by, disease., , 9.2 INTRODUCTION, Plants are primary producers of food. Man‘s other necessities(like fibers for clothing,, timber for buildings and furnituremanmedicines for health, fuel for source of energy., for different activities also) basically originate from plants. They represent the only machine, known so far that can directly convert solar energy into food. Thus plants are the very pivot, of our existence on earth and without plants the earth will be without life., This unavoidabledependence of not only man but also other forms of life whichhelp, man has its own implications which man has to reckon with. In the ancient times there was, not much struggle for food since the population was low and the available per capita in, plenty. In the light of above consideration of plants and man relationship and increasing, demand on food sources, it is worthwhile to consider how food production can be increased, by at least 75% to meet the food demand of the population to be fed in the next 20 to 25, years. At the present time, nearly 350 crore acres of land of about12% of the earth‘s total, surface area is cultivated and used for essential crop production., Modern technology and increase in the value of food crops have brought almost the, maximum area under cultivation. Thus targets for increased food production per unit area, already available for cultivation., Limitations in management of large acreages, adverse weather andnatural calamities, and most important of all, the attack of pests and disease are the main cause of reduced yields, from otherwise high potential crop varieties., , What is plant disease?, When a plant is suffering, we call it diseased. However, this does not define the term, ‗disease‘. Often the symptoms produced by a disease, the cause of the disease, and the, injuries caused to the plant have been considered synonymous with the term disease., However, they signify only the condition of the plant due to disease or the cause of the, disease., Disease can be defined as a pathological process. Some of the recent definitions are –, , UTTARAKHAND OPEN UNIVERSITY, , Page 210
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , ―Disease is a malfunctioning process that is caused by continuous irritation which, results in some suffering producing symptoms‖., ―Disease is of the normal chemical reactions that are inhibited or the abnormal, chemical reactions induced inside the cells and in the tissues of the plant as a result of the, irritation brought about by the causal agent‖., When a plant is diseased it is at ‗dis - ease‘. It means that the plant is uneasy due to some, condition to which its system is not accustomed. When a man is in uneasy position he usually, loses his efficiency but sometimes he does not, and becomes accustomed to it and so, maintains his efficiency., Similarly, when a plant is at ―unease‖ it may loss its efficiency or may not. For a practical, plant pathologist (or for the farmer) it is the loss of efficiency of the plant that is important., Hence a practical definitionof plant disease can be as given condition of a plant when its, systems are not normal and therefore it is not producing as good as it should according to, normal expectations of the farmer. The cause of infection in plants may be different kinds of, microorganisms (Fig.9.1)., , Fig.9.1: Causes of infection in plants, , The Importance of Plant Diseases, Plant diseases are important because of the loss they cause. The loss can occur in the, field or in the store and at any time between sowing and consumption of the harvest. Standing, crop in the field is attacked by a disease and plants start drying or their capacity to yield, satisfactorily is reduced. Thus farmer gets only a portion of the estimated yield., Microorganisms destroy perishable food materials in the store. There is no doubt that, a big portion of this stored food does not reach to the mouth of hungry millions.In the history, , UTTARAKHAND OPEN UNIVERSITY, , Page 211
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , of mankind, plant diseases have been connected with a number of important events. Some of, the important events are mentioned below., The late blight of potato is a famous example of what a plant disease can do to change, thecourseofhistory.In1845thisdiseasedestroyedthepotatocropofIreland., In, England,, IrelandandcertainpartsofcontinentalEuropepotatowasstapledietofthepopulation. Thisdisease, hadstartedinthesecountriesasearlyas1830andeveryyear, it, wascausingsome, damageresultinginfoodshortage.InEngland,freetradeandimportoffoodgrains wasnotpermitted., Whentheepiphytoticoflateblightdestroyedpotatocropin1845,therewasfamineinthesecountrieses, peciallyinIreland. In this country alone, the population of 80 lacs was reduced to 60 lacs., A large number of people died of hunger and many more become diseased due to, physical weakness. This single disease forced man to realize the importance of plant disease., As a result, scientific investigations were taken up, the cause of the disease was identified and, extensive use of chemicals for plant disease control came into existence., Wheat rust has been another disease that has appeared in epiphytotic form from time to time, in many countries. This disease forced the farmers in many parts of the world to change their, cropping patterns. In the last years of the Second World War (1943) Bengal had to face a, serious famine. One of the reasons to which this famine has been attributed is the loss in yield, of rice due to attack of Helminthosporium leaf spot which had been affecting the crop for the, last several years., These instances of plant disease epidemics are worth mentioning because they left their, effects not only in the country concerned but also in other countries. Ordinarily plant diseases, affect every crop, every year and in all parts of the world. This results in huge loss of, potential production, and money. In addition to direct loss in yield sand monetary returns, the, plant diseases affect the society in many other ways. When food grains are attacked by, certain fungi they may contain toxins which cause insanity, paralysis, stomach disorders etc,, in human beings and animals. The money spent in the control of plant disease is also a loss, which could be saved in absence of disease., Agriculture based industries are also affected by plant diseases. Industries that consume, raw materials produced in agriculture (cotton, oilseeds etc) face difficulty in utilizing their, capacity when there is less production due to plant diseases. In order to make up for the loss, of food production, the governments have to import food which means loss of foreign, exchange at the disposal of government. Excessive use of pesticides, weedicides leads to, environmental pollution which affects health of human beings., , 9.3 -STAGES INDISEASE DEVELOPMENT: DISEASE CYCLE, In an infectious disease there is a series of more or less distinct events which occur in, sequence and lead to development and perpetuation of the disease and the pathogen, (Fig.9.2). This chain of events is called a Disease cycle. The disease cycle involves, the changes in the plant and symptoms as well as those in the pathogens, and spans, , UTTARAKHAND OPEN UNIVERSITY, , Page 212
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , periods within a growing season and from one growing season to the next. The main, events of a disease cycle include., [I] inoculation [II] prepenetration [III] penetration [IV] infection (also includes invasion)[, V] growth and reproduction of the pathogen [VI] dissemination of the pathogen, and[VII] seasonal carry-over of the pathogen., , Fig.9.2: Various events of disease development, , 1. Inoculation– Inoculation is the contact of a pathogen with a plant. This is the, inoculum that lands on or otherwise brought into contact with plant. Inoculum is any, part of the pathogen that can cause infection. In fungi, inoculum may be spores,, sclerotia or mycelial fragments. In bacteria, mycoplasmas, viruses and viroids,, inoculum is always whole individuals. In nematodes, inoculum may be adults, larvae, or eggs, whereas in parasitic higher plants it is plant fragment or seed. Inoculum that, survives the off season periods (winter or summer) and causes the original infection in, the growing seasons is called primary inoculum, and the infections as primary, infections. Inoculum produced from these primary infections. It actually spreads the, disease in the field under favourable conditions, and is called secondary inoculum., This brings about secondary infections. Inoculum in the absence of its host from the, field survives in plant debris, field soil, seed, tubers, transplants or other plant parts,, perennial weeds, alternate hosts. The inoculum is carried to host plants and this, landing or arrival of inoculum is possible by wind, water, insects etc or in some cases, also by active growth as in some root-infecting fungi like Armillaria mellea., 2. Prepenetration- This phase include all the events prior to actual entry of the, pathogen. Such events include (i) germination of spores and seeds, (ii) hatching of, eggs (nematodes), (iii) attachment of pathogen to host, and (iv) recognition between, host and pathogen (early event-not still understood clearly). Lack of specific, recognition factors in plant surface may not allow the attachment of pathogen to it., UTTARAKHAND OPEN UNIVERSITY, , Page 213
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Such factors in plant include lectins (proteins or glycoproteins) and some oligo-and, polysaccharides., 3. Penetration- This is the actual entry of the pathogen into their host plants., Pathogens penetrate plant surfaces in different ways: (i) Direct penetration through, intact plant surfaces. (ii) Through natural openings, and (iii) Through wounds., 4. Infection- Infection is the process by which a pathogen establishes contact with host, cells or tissues and procures nutrients from them. Penetration does not always lead to, infection and many organisms actually penetrate the cells but plants may not become, diseased, These organisms are not able to proceed beyond penetration. However effective, pathogens are able to invade further and cause infection. Various pathogens invade hosts in, different ways and through different extents. Some fungi produce mycelium which grows, only in the area between the cuticle and epidermis, other produce mycelium only on the, surface of host plant sending only haustoria into epidermal cells. Most fungi spread into all, the tissues (Chiefly parenchyma of mesophyle and cortex) of plant organs (leaves, stems,, roots etc.) they infect. They grow directly through the cell (intracellular mycelium) or, between the cells (intercellular mycelium). The fungi that cause vascular wilts invade the, xylem vessels of plants., During infection pathogens grow and multiply within the plant tissues and invade the, plant to varying extents. Individual fungi and parasitic higher plants generally invade and, infect tissues by growing into them from one initial point of inoculation. For a pathogen, to, infect a plant, it must be able to make its way into it and through the plant and obtain, nutrients from it the plant and neutralize the defense mechanisms of the plant., , Fig.9.3: Showing three way interaction, , UTTARAKHAND OPEN UNIVERSITY, , Page 214
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 9.4: PLANT DISEASE RESISTANCE, Plant disease resistance protects plants from pathogens in two ways: by performed, mechanisms and by infection-induced responses of the immune system. For a susceptible, plant, disease resistance is the reduction of pathogen growth on or in the plant, while the term, disease tolerance describes plants that exhibit little disease damage despite substantial, pathogen levels. Disease outcome is determined by the three way interaction of the pathogen,, the plant and the environmental conditions -an interaction known as the disease triangle, (Fig.9.3)., Defense activating compounds can move from cell to cell and systemically through, the plant vascular system. However, plants do not have circulating immune cells, so most cell, types exhibit a broad suite of antimicrobial defenses. Although obvious qualitative, differences in disease resistance can be observed when multiple specimens are compared, (allowing classification as ―resistant‖ or ―susceptible‖ after infection by the same pathogen, strain at similar inoculum levels in similar environments), a gradation of quantitative, differences in disease resistance is more typically observed between plant strains or, genotypes. Plant consistently resist certain pathogens but succumb to other, as resistance is, usually pathogen species- or pathogen strain-specific., Different plants are resistant to certain diseases for various reasons. Some plants are, immune to a particular pathogen even under most favorable conditions for disease, development other exhibit some degree of resistance to a pathogen under most environmental, conditions, still others are actually susceptible to the pathogen but under the conditions they, are normally grown may appear resistant. Somevarieties show tolerance to a disease and can, produce good crop in spite of infection., , Resistance:, Vertical (specific):, Resistance of a plant to a pathogen is provided by one or a few defense mechanisms, controlled by one or a few genes respectively and is either monogenic (one gene) or, oligogenic. Thus a given variety has resistance effective only against some races of a, pathogen but not against other races., , Horizontal (general), In horizontal type, resistance to a plant variety is provided by a combination of lesser, defense mechanisms, each of which alone is rather ineffective against the pathogen.Such, mechanisms are controlled by a group or groups of complementary genes. Thus, with, horizontal resistance, a given variety of plant is more or less uniformly resistant to all races of, a pathogen., , Plant breeding for disease resistance, The value of resistance in disease control was recognized in the early 1900s.Advances, in genetics and dangers of pollution by chemicals provided additional impetus in this area., UTTARAKHAND OPEN UNIVERSITY, , Page 215
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , There have been efforts throughout the world on breeding plants that combine the most useful, genes for higher yields,better quality, uniform ripening and disease resistance. Thesources of, genes for resistance areeither native or foreign commercial or, wild plant varieties etc., Plant breeders emphasize selection and development of disease-resistant plant lines., Plant diseases can also be partially controlled by use of pesticides and by cultivation practices, such as crop rotation, tillage, planting density disease-free seeds and cleaning of equipment,, but plant varieties with inherent (genetically determined) disease resistance are generally, preferred. Breeding for disease resistance began when plants were first domesticated., Breeding efforts continue because pathogen populations are under selection pressure for, increased virulence, appearance ofnew pathogens, evolving cultivation practices and, changing climate can reduce resistance and/or strengthen pathogens.Plant breeding for other, traits can disrupt prior resistance. A plant line with acceptable resistance against one, pathogen may lack resistance against others., , Breeding for resistance typically includes:, , , , , , , , Identification of plants that may be less desirable in other ways, but which carry a, useful disease resistance trait, including wild strains that often express enhanced, resistance., Crossing of a desirable but disease-susceptible variety to another variety that is a, source of resistance., Growth of breeding candidates in a disease-conducive setting, possibly including, pathogen inoculation. Attention must be paid to the specific pathogen isolates, to, address variability within a single pathogen species., Selection of disease-resistant individuals that retain other desirable traits such as, yield, quality and including other disease resistance traits., , Resistance is termed durable if it continues to be effective over multiple years of widespread, use as pathogen populations evolve. ―Vertical resistance‖ is specific to certain races or strains, of a pathogen species, it is often controlled by single R genes and can be less durable., Horizontal or broad-spectrum resistance against an entire pathogen species is often only, incompletely effective, but more durable, and is often controlled by many genes that, segregate in breeding populations., Crops such as potato, apple, banana and sugarcane are often propagated by vegetative, reproduction to preserve highly desirable plant varieties, because their species outcrossing, seriously disrupts the preferred traits. Vegetatively propagated crops may be among the best, targets for resistance improvement by the biotechnology method of plant transformation to, manage genes that affect disease resistance., , Gmor transgenic diseases resistance, The term GM (Genetically Modified) is often used as a synonym of transgenic to refer, to plants modified using recombinant DNA technologies. Plants with transgenic/GM disease, resistance against insect pests have been extremely successful as commercial product,, especially maize and cotton, and are planted annually on over 20 million hectares in over 20, UTTARAKHAND OPEN UNIVERSITY, , Page 216
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , countries worldwide . Transgenic plant disease resistance against microbial pathogens was, first demonstrated in 1986. Expression of viral coat protein gene sequences conferred virus, resistance via small RNAs. This proved to be a widely applicable mechanism for inhibiting, viral replication. Combining coat protein genes from three different viruses, scientists, developed squash hybrids with field-validated, multiviral resistance. Similar levels of, resistance to this variety of viruses had not been achieved by conventional breeding., A similar strategy was deployed to combat papaya ring spot virus, which by 1994 threatened, to destroy Hawaii‘s papaya industry. Field trials demonstrated excellent efficacy and high, fruit quality. By 1998 the first transgenic virus-resistant papaya was approved for sale., Disease resistance has been durable for over 15 years. Transgenic papaya accounts for ~85%, of Hawaiian production. The fruit is approved for sale in the U.S. Canada and Japan., Potato lines expressing viral replicase sequences that confer resistance to potato leafroll virus, were sold under the trade names Newleaf Y and Newleaf plus and were widely accepted in, commercial production in 1999-2001, until McDonald‘s crop. decided not to purchase GM, potatoes and Monsanto decided to closer their Nature Mark potato business. Newleaf Y, Newleaf Plus potatoes carried two GM traits, as they also expressed Bt-mediated resistance to, Colorado potato beetle., No other crop with engineered disease resistance against microbial pathogens had reached the, market by 2013, although more than a dozen were in some state of development and testing., Example of transgenic disease resistance projects, Publication year, , Crop, , Disease resistance, , Mechanism, , Development, status, , 2012, , Tomato, , Bacterial spot, , R gene from pepper, , 8 years of field, trails, , 2012, , Rice, , Bacterial blight and, bacterial streak, , Engineered E gene, , Laboratory, , 2012, , Wheat, , Powdery mildew, , Overexpressed R, gene from wheat, , 2 years of field, trials at time of, publication, 4 years of field, trials at time of, publication, , 2011, , Apple, , Apple scab fungus, , Thionin gene from, barley, , 2011, , Potato, , Potato virus Y, , Pathogen-derived, resistance, , 1 year of field trial, at time of, publication, 12 years of field, trials at time of, publication, Laboratory scale, , 2010, , Apple, , Fire blight, , Antibacterial protein, from moth, , 2010, , Tomato, , Multibacterial, resistance, , PRR from, Arabidopsis, , UTTARAKHAND OPEN UNIVERSITY, , Page 217
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 2010, , Banana, , Xanthomonas wilt, , Novel gene from, pepper, , Now in field trial, , 2009, , Potato, , Late blight, , R genes from wild, relatives, , 2 years of field, trials, , Late blight, , R gene from wild, relative, , 2 years of field, trials at time of, publication, , 2009, , Potato, , 2008, , Potato, , Late blight, , R gene from wild, relative, , 2 years of field trials at, time of publication, , 2008, , Plum, , Plum pox virus, , Pathogen-derived, resistance, , Regulatory approvals,, no commercial sales, , 2005, , Rice, , Bacterial streak, , R gene from maize, , Laboratory, , Stem rust, , Resting lymphocyte, kinase (RLK) gene, from resistant barley, cultivar, , Laboratory, , 2002, , Barley, , Papaya, , Ring spot virus, , Pathogen-derived, resistance, , Approved and, commercially sold, since 1998, sold into, Japan since 2012, , 1995, , Squash, , Three mosaic, viruses, , Pathogen-derived, resistance, , Approved and, commercially sold, since 1994, , 1993, , Potato, , Potato virus X, , Mammalian, interferon induced, enzyme, , 3 years of field trials at, time of publication, , 1997, , Defence mechanisms of plants against pathogen, The defence mechanisms of plants against pathogens fall into two categories:1. Morphological or structural defence mechanism., 2. Biochemical defence mechanism, , 1. Morphological or Structural Defence Mechanism, The first line of defence against pathogen is the surface barrier, which a pathogen, must penetrate before it can cause infection. The entry of the pathogens may either be, through the epidermal cell walls directly or through the natural openings in the epidermis,, such as stomata, lenticels and hydathodes, or through injured areas caused by living or nonUTTARAKHAND OPEN UNIVERSITY, , Page 218
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , living agencies. Certain structural features oftheepidermisor its interior may greatly affect the, ability of the pathogen to penetrate or invade a host plant. Such morphological defence, structures may be present before penetration or infection or may be produced afterwards as a, result of the interaction of the host and the pathogen., , Defence Structures Existing Before Infection –, Waxes and Cuticles -The cuticle, which consists of cutin and waxes, forms the outermost, covering of the epidermal cells and appears as a non-cellular, membranous layer. Waxes play, a defensive role by forming a hydrophobic surface which acts as a water repellent and there, by prevent the retention of water on sloping plant surfaces on which pathogens might be, deposited and subsequently invade the host. The cuticle acts as a physical or chemical barrier, to infection., , Epidermal cell wall– Lignification or the presence of silicic acid in the epidermis of some, plants act as an important structural defence mechanism., , Defence Structures Formed after infection: Defence structures are produced inside the host plant to block or prevent the spread of, the pathogen. These include the formation of cork layers, tyloses and abscission layers,, deposition of gums, resins and tannin like substances, swelling of the cell walls, sheathing of, hyphae and so on., , 2. Bio-Chemical Defence–, Phenolic Substances - Resistance to several fungal plant pathogens has been ascribed to, higher concentrations of fungitoxic phenolic substances and their oxidation products and to, increased polyphenol oxidase (PPO) activity which generally, but not invariably, results from, infection. The activity of poly phenol oxidase (PPO) seems to be important because it can, oxidize phenolies to Quinones which may be more fungitoxic. PPO produced by the pathogen, may oxidize the host polyphenols to more highly fungitoxic substances, which may prevent, further development of the pathogens. It has been reported that aromatic substances such as, polyphenols, phenolic glucosides, flavonoids, anthocyamins and aromatic amino acids etc, tend to accumulate in and around infected plant tissue and also intissues adjacent to wounds, where presumably, they might exert a fungistatic effect. Some of the most important phenolic, compounds involved in the defence of plants are caffeic acid, ferulic acid, chlorogenic acid,, phloretin and various phytoalexins., , Phytoalexins:-Phytoalexins can be described as low molecular weight antimicrobial, compounds that accumulate in plants as a result of infection or stress. The term, ‗Phytoalexins‘ was introduced by Muller and Boerger (1940) to describe the substances that, inhibit fungus development. These substances are formed when living plant tissues are, invaded by a fungal parasite., , UTTARAKHAND OPEN UNIVERSITY, , Page 219
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 9.5 - GENERAL SYMPTOMS OF PLANT DISEASES, As a result of successful infection of host plant by the pathogen, a number of, physiological changes occur in the plant. Respiration, photosynthesis, nitrogen metabolism,, and transpiration are affected.In most cases host respiration increases after infection. There is, reduced rate of photosynthesis in many diseases. Metabolites like carbohydrates, amino acids, and proteins tend to accumulate in green islands. Normally, there is an increase in, transpiration rates., The physiological changes occurring in the diseased plant have their counterparts in, the anatomical and morphological changes (morbid anatomy). Anatomical and morphological, changes are brought about by affecting individual cells and growth of entire plant or of an, organ, vegetative as well as floral. Thus, changes in physiology of plants due to infection, result into several anatomical and morphological changes which are expressed externally in, the form of visible symptoms. Symptoms are characteristic of a disease by which it can be, recognized in the field., In some cases, however two different pathogens can produce identical symptoms and, a single pathogen can develop more than one kinds of symptoms i.e. disease syndrome., Types of symptoms are as varied as the pathogens. For instance different groups of pathogens, cause a variety of symptoms. These are mentioned below:, , Myxomycetes and phycomycetes- Galls, scab, warts, rots, blights, damping off, white, rusts, downy mildews etc., , Ascomycetes and Fungi Imperfectii- Leaf curls, powdery mildews,cankers, leaf, spots,anthracnose,root and stem rots,vascular wilts,scab,fruit and vegetable rots, early blight, etc., , Basidiomycetes- Rusts,smuts,root and stem rot,wood rots etc., Bacteria- Galls,rots,blights,spots,cankers,scab,vascular wilts etc., Mycoplasma- Aster yellows,proliferation,general yellowing,stunting,phloem necrosis etc., Viruses-Mosaics and mottles, ring-spots, dwarfing, rolls, yellows, galls and tumors, pitting, etc., , Nematodes-Root knots [galls], root lesions, excessive root branching, root rots. Galls,, lesions and rots on leaf, stem, galls in grains etc., General Symptoms caused by different groups of pathogens are shown in (Fig.9.4- 9.9)., These enormous variety of symptoms, basically belong to any of the three main, categories; (A)-Necrosis (B)-Hypertrophy and Hyperplasia, and (C)-Hypoplasia., , UTTARAKHAND OPEN UNIVERSITY, , Page 220
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.9. 4: Hypertrophy and Hyperplasia symptoms, , [A]NecrosisNecrosis is the commonest and most destructive type of effect.This kind of symptoms, is produced by rather unspecialized parasites. Among these pathogens, the most destructive, ones, Pythium, Botrytis, Fusarium showing wilts and many other symptoms. These, pathogenscause immediate and severe damage to host tissues and obtain their nutrients from, cells killed in advance by secretion of enzymes and toxins.They are thus called necrotrophs., Some other necrotrophs, somewhat intermediate group between the above mentioned ones, (and the specialized parasites as rusts,mildews etc),do not kill cells in advance but invade and, thenkill the host cells. Such necrotrophs include fungi like Phytophthora, Venturia, Taphrina, and Claviceps., Necrosis is caused by specialized parasites like rusts,mildews,smuts but only in later, stages of development when they sporulate. Thus, during early stages of infection there is, only slight adverse effect.Necrosis is also caused by bacteria and viruses., The symptoms of necrotic nature are as follows:, , 1-Leaf spots: The cells are killed in a limited area to form lesion or spots.The spots are of, various size and shape as zonate,target board, angular,frog eye etc.Tar spots are characteristic, type of leaf spots which appear as raised,black coated fungus bodies giving the appearance of, a flat drop of tar on leaves. Example Rhytisma and Phyllachora.In some cases, the dead, tissue shrinks and separates from the healthy tissue. This condition is known as Shot Hole., , UTTARAKHAND OPEN UNIVERSITY, , Page 221
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.9. 5: Leaf spots symptoms, , 2-Streaks or Strips-: These are elongated, narrow lesions on leaves, which are usually of, brown shade. Example-Bareley stripe by Helminthosporium., , 3-Blights: This gives a burnt appearance.There is sudden death of plant parts as leaves,, blossoms, stamens, or twigs or even entire plant.The dead part usually turns brown or black, and soon disintergrates. Example-early and late blight of potatoes. Some bacteria e.g., xanthomonas also cause blight symptoms in may plants., , Fig.9.6: Blight symptoms, , 4-Damping off: This is the condition where the stem is attacked near the ground level.The, affected portion becomes constricted and weak, and finally disintegrates causing the seedling, to topple down and die.Damping off of vegetable seedlings is common and caused by, Pythium and Phytophthora., , 5-Burn, Scald or Scorch: In succulent plant parts, like fruits, limited areas necrose, die, and turn brown., , UTTARAKHAND OPEN UNIVERSITY, , Page 222
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 6-Rots:The infected tissue dies,decomposes rapidly and turns brown.Fungi and bacteria, which are able to dissolve cell walls cause this symptom.The examples include root-rot,leaf, rot,stem rot,bud rot and fruit rot., , 7-Wilting: Wilting of infected leaves occurs perhaps due to plugging of xylem vessels by, fungus or mucilaginous substances. It is caused by some fungi like Fusarium spp. and, Trichometasphaeria turcica (in maize). Later, the whole plant wilts and dies., 8-Die-back: Death of plant part,such as stem or branches the from tip back-wards., 9-Cankers:A canker is a dead area in the bark or cortex of woody stems.There are often, large areas with definite margin.Dead bark splits and falls away. Example-Citrus canker, (bacterial)., , 10-Chlorosis: Discolouration from normal colour is common in some cases.The green, pigment may be destroyed and the tissue becomes yellow.This condition is known as, chlorosis, caused by viruses, bacteria and some fungi., , 11-Blotch: Some fruits,due to infection,develop superficial growth appearing as a blotch, area.It occurs in sooty blotch and fly speck disease of apple., , 12-Scab: This is a rough,crust-like lesion or a freckled organ.It occurs mostly in fruits and, vegetables.Examples- apple scab by Venturia inaequalis., , 13-White blisters or pustules: On leaves of some plants there numerous shining white, blister-like pustulesdevelop which break open at maturity exposing powdery mass of, spores.Such diseases are commonly called white rusts caused by Albugo spp., 14-Smuts: This refers to a sooty or charcoal-like powdery mass.In plants infected by smuts, (Ustilago, Tilletia), this is very common. Smut spores develop mostly in floral organs,, particularly ovaries; other affected organs include leaf, stem and roots., , Fig.9.7: Smut symptoms, , 15-Rusts: The rusts appear as small pustules of spores forming a powdery mass of brownish,, red, yellow or dark brown colour. These break through epidermis. Example- members of, uredinales. Rusts disease of wheat is quite common., , UTTARAKHAND OPEN UNIVERSITY, , Page 223
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.9.8. Rust symptoms, , 16-Mildews: In this case the pathogens grow mostly superficially on host surface.They, appear as white,grey, brownish or purple patches of various sizes on leaves.In case of Downy, mildew(Peronosporaceae),the superficial growth is a tangled cottony or downy layer, consisting of sporangiophores and sporangia of the pathogen. In Powdery mildew, (Erysiphaceae), there is superficial, white powdery growth of mycelium, numerous, conidiphores and conidia. These give a dusty appearance., , Fig.9.9. Powdery mildew symptoms, , [B] Hypertrophy and Hyperplasia (over-development), In some diseases,there is abnormal increase in size of an organ or of the entire, plant.This increase may be due to increase in size of individual cells of affected tissue,, i.e.,hyperplasia.Various overgrowths developed are of the following types., , 1-Elongated internodes: some infected plants develop elongated internotes and become, abnormally tall. Example-rice infected with Giberella fujikuroi, Euphorbia cyperissias with, Uromycespisi, sugarcane with Sclerospora sacchari., , 2-Galls and tumors: These are globose, elongated or irregular large sized out-growths, formed on attacked part.Smaller galls are warts tubercles. Examples are club-root of, crucifers, some species of Albugo, crown-gall tumors, root knot etc., UTTARAKHAND OPEN UNIVERSITY, , Page 224
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 3-Witche’s broom: They are formed by fungi (Taphrina, some rusts), bacteria (Coryne, bacterium fasciens), and certain viruses as well as insects and mites. They arise basically, from stimulation of structures which normally remain dormant, such as buds. The broom very, often appears as an upright cluster of small shoots,contrasting with horizontal growth habit of, normal shoots., , 4- Curls: In some diseases the leaves are arched,puckered, twisted,curled and distorted., Example-peach leaf curl (Taphrima deformans), papaya leaf curl (Virus)., , 5-Floral abnormalities: some fungi, such as Albugo candida cause the infected, inflorescence toenlarge; it becomes green and fleshly with stamens converted into leafly, structures. The inflorescence becomes distorted., , [C] Hypoplasia (under-development), In these instances,there is reduced development of the whole plant, plantparts,certain flowers, or fruits (sterility),or of chlorophy II (chlorosis). In extreme cases,it leads to atrophy in which, the organ or tissue does not develop at all., , 1.Chlorosis: Reduced development of chlorophyll results into various kinds of chlorosis,, mosaic and mottling in many viral and deficiency diseases. Chlorosis may take the form of, streaking. There may be Vein clearing-a translucent appearance of the veins or vein banding, in which dark green bands bound the veins or a general chlorosis of the whole leaves turning, them yellows., 2. Reductionof Individual Organ: Individual leaves and flowers may be reduced in size, and/or altered in shape. Reduced leaves develop in viral infections and in some fungi such as, Exobasidium. Examples are ―fern leaf‖,where lamina disappears, ―little leaf‖ etc. Inter modes, are reduced in dwarf bunt of wheat caused by Tilletia contraversa, and in several viral, diseases., , 3.Floral Abnormalities: In smut of Caryophyllaceae members, stamens become sterile, (caused by Ustilago violacea). One very common and characteristic floral abnormality is, Phyllody, i.e., transformation of floral parts into green leafy twisted structures. These are, caused by mites, insects, fungi and viruses. Example- green ear disease of bajra., , 9.6 - SUMMARY, Disease is a complex phenomenon and thus difficult to define in a few, words.According to modern concept, disease results from an interaction among the host,, parasite and environment. Diseased plants are distinguished by changes in their, morphological structures or physiological processes,which are brought about by unfavorable, environmental conditions or by parasitic agents., Sometimes variation in the environment also makes a plantsusceptible to infection., The microorganisms are thus not the sole causal factor. After a microorganism has, , UTTARAKHAND OPEN UNIVERSITY, , Page 225
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , successfully infected a susceptible plant, the subsequent interaction between the plant and the, microorganism is also affected by environmental influences., Most casual organisms are parasites. A parasite is not synonymous with the pathogen., The mycorrhizal fungus is certainly parasitic on the roots of trees but is not pathogenic.In a, literal sense, a pathogen is any agent that causes damage. Most, but not all pathogens, are also, parasites in that they derive the materials needed for existence from a living plant. The, sequence of processes in disease development starts from the initial contact between a, pathogen and its host until to the completion of thesyndrome., A large number of plant diseases and sometimes the scale of destruction they cause,, suggests that diseases can even change the course of history and the economy of a country., They of course are a limiting factor in crop production. The advances made in food, production in developing countries due to green revolution could be offset if proper attention, is not given to plant diseases and pests., , 9.7 - GLOSSARY, Appresorium: An enlarged, usually disc shaped structure formed at the tip of hypha of some, parasitic fungi from which entry is made into the host., Autotrophic: An organism capable of utilizing energy from light for metabolic synthesis., Aetiology(Etiology) – The science of the cause of diseases., Autoecious: Completing the lifecycle on one host., Biotroph: Living on living cells., Biological control: Control of a disease by the activity of other organisms., Blight: A necrotic symptom on leaves which is characterized by sudden and serious leaf, damage., Centrifugal: From the centre outwards., Centripetal: Towards the centre., Ceraceous: Wax – like., Coenocytic: A multinucleate mass of protoplasm, noncellular, in the sense of being non, septate., Canker: A necrotic symptom of woody parts. The wound is surrounded by a raised tumor, like margin., Chlorosis: Symptom of chlorophyll deficiency., Disease: A malfunctioning process due to continuous irritation from the presence or absence, of some agent., Dioecious: The organism in which the male and female sex structures are on different thalli., , UTTARAKHAND OPEN UNIVERSITY, , Page 226
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Diplanetism: The condition in which there are two motile stages with a resting stage in, between., Diplobiontic: Having haploid and diploid generations as free living individuals., Epidemic: Widespread and destructive development of a disease in a large human, population., Epidemiology: The study of epidemics., Etiology: The study of the causal agents of a disease and its relation to the susceptible plant., Fungicide: A chemical that reversibly inhibits the growth of a fungus as long as it is in, contact with the fungus., Gall: A tumor, formed by hyperplastic growth of unorganized cells., Heteroecious: Undergoing different parasitic stages on two unrelated hosts., Haustorium: A special hyphal branch within the living cell of the host, for absorption of, food., Heterothallism: Condition of sexual reproduction in which conjugation is possible only, through the interaction of different thalli., Heterokaryosis: The state of a fungus having genetically different nuclei in its cells., Heterotrophic: Organism deserving food from other living or dead organisms; unable to, synthesize organic material from inorganic sources., Host: A living organism providing sustenance to a parasite., Hyperplasia: Outgrowth due to abnormal increase in the division of cells., Hypertrophy: Outgrowth due to abnormal increase in size of the cells., Inoculum: Portion of pathogen capable of dissemination and initiation of disease., Immune: Resistant from infection., Innate: Immersed., Karyogamy: The fusion of two sex nuclei after cell fusion, i.e., after plasmogamy., Metula: A conidiophore branch having phialides., Monoecious: Having genetically identical haploidnuclei., Mould: A micro fungus having a well-marked mycelium or spore mass., Mycelium: A mass of hyphae; the thallus of a fungus., Mycorrhiza: A symbiotic, non- pathogenic or feebly pathogenic association of a fungus with, the roots of a plant., Mycosis: A fungal disease of humans and animals, rarely of plants., Necrosis: Death of cells., Parasite: An organism that derives its food from a different species of plant., UTTARAKHAND OPEN UNIVERSITY, , Page 227
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Pathogen: Causal agent of a disease., Pathogenic: Capable of causing disease., Protectant: A substance, usually a fungicide that prevents infection., Pustule: A pimple like eruption of host tissue formed by fruiting body, such as uredium or, telium, in case of rust disease., Resistance: The inherent capacity of a plant to prevent, restrict or withstand disease., Rogue: To remove unwanted plants., Sign: Visible structures of pathogens appearing on or in diseased tissue., Symptom: A visible expression of disease in the host plant., Syndrome: The pattern of symptoms and signs of a disease., Systemic: Which spreads throughout the plant body., Tolerance: The ability of a host to survive and give satisfactory yield when other varieties of, the same species suffer great loss., Variety: Subdivision of a species that differs from the type species in certain characteristics., Vector: An agent that causes dissemination of a pathogen., Virulence: Relative ability to cause disease, a measure of pathogenicity., , 9.8- SELF ASSESSMENT QUESTION, 9.8.1: Fill in the blanks –, 1. The word fungus is derived from the latin word………………….., 2. The fungi which grow on dead or decaying organic matter are called…………….., 3. Monoccious fungus is that which bears male and female sex organs on the, …………thallus., 4. The Study of plant disease is known as …………………….., 5. The chemicals used for killing fungal pathogen are called…………………., 6. Loose smut of wheat is caused by…………………….., 9.8.1: Answers Key: 1. Fungous, 2. Saprophytes, 3. Same, 4.Plant pathology, 5.Fungicides,, 6. Ustilago tritici, , 9.8.2: Differentiate between –, 1., 2., 3., 4., 5., , Hypertrophy and hyperplasia, Parasitic and non-parasitic diseases., Black rust and white rust., Epidemic and endemic diseases., Obligate parasite and obligate saprophytes., , UTTARAKHAND OPEN UNIVERSITY, , Page 228
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 9.8.3: Write short notes ona., b., c., d., e., f., g., , Disease, Fungicides, Infection, Prepenetration, Haustoria, Quaranine, Phytoalexins, , 9.9 REFERENCES, , , , , , , , , , , , , , , , , , Anonymous (1995), ―Epidemiology,crop loss assessment, Phytopathometry‖,Cam. J. Pl., Pthol. , 17:98 – 189., Brown, W. (1965), ―Toxins and cell wall dissolving enzymes in relation to plant disease.‖, Ann Rev. Phytopath. , 3:1-18., Collmer, A and N: T. Keen (1986), ―The role of pectic enzymes in plant pathogenesis‖, Ann. Rev. Phytopathol. , 24:383-409., Dodds , P.N. , Rathjen , J.P. (2010) ― Plant immunity : Towards an integrated plant, pathogen interactions‖ nature Reviews genetics 11(8) : 539., Eide , J.C.(1955) , ― Fungus infections of plant‖ , Am. Rev. Microbiol. , 9:297 – 318., Jones, J.D., Dangl , J.L.(2006) ―The plant immune system‖ Nature 444(7117) : 323 -329., Kuc, J. (1963), ― Role of phenolic compounds in disease resistance‖ , in: Perspectives, ofBiochemical plant pathology, S.Rich (Ed.) , Coon . Agr. Ex. Sta (New Haven). Bull.,, 663: 20 – 25., Mehrotra , R.S. , Aggarwal, A (2006) ―Plant Pathology‖ Second edition , Tata MC Graw, Hill Publishing company Limited., Mehta P.R.(1963), ― Plant Pathology in India – Past, present and prospects ― Indian, Phytopath , 16 : 1 – 7, Nagarajan , S. (2000), ― Plant Pathology and Indian Agriculture – Past, present and, future‖ Indian phytopath. , 53(2) : 121- 128., Owens, L.D.(1969), ― Toxins in Plant disease : Structure and mode of action.‖ Science ,, 165 : 18 – 25., Ray Chaudhuri , S.P. (1991) ― Development of Mycological and plant pathological work, in India‖ , Indian J. Mycol. Plant Pathol. , 21: 14- 26., Strobel , G. A. (1974) , ― Phytotoxins produced by plant parasites‖ , Ann. Rev. Pl., Physiol. , 25 : 541 – 566., Schumann , G. (1991) ― Plant diseases : Their biology and social impact‖ APS press St., Paul , MN ISBN 0890541167., Singh R. S. , 1983 ― Plant diseases‖: Fifth edition Oxford & IBH Publishing co., , UTTARAKHAND OPEN UNIVERSITY, , Page 229
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , BSCBO-101, , Stakmann , E.C. (1958), ― The role of plant pathology in the scientific and social, development of the world in plant pathology‖ , in : Plant pathology – problems and, progress, C.S. Holton et.al, (Eds.) Univ. of Wisconsin Press, Madison, PP- 3- 13., Vidhyasekaran, P.(1998), ―Molecular biology of pathogenesis and induced systemic, resistance‖ , Indian Phytopath. , 5 (2): 111 – 120., , 9.10-SUGGESTED READING, 1. Agrios, G.N.(1997), ―Plant pathology‖ Fourth Edition, Academic Press , San Diego,, California., 2. Mims, C.A.(1995), ―The pathogenesis ofinfectious disease‖. 5th Edition Academic Press., London., 3. Singh, R.S.(1998), ―PlantDiseases‖ Oxford and IBH PublishingCo.Pvt.Lt., New Delhi., 4.Mehrotra,R.S. andAshokAggarwal (2006), ―Plant Pathology‖, SecondEditionTataMcGrawHillPublishing Co.Pvt.Lt., New Delhi., , 9.11 TERMINAL QUESTIONS, Q.1-What is disease? Discuss the components of disease and the kinds of diseases in, plants., Q.2- Discuss the general process of infection in plant pathogens., Q.3- Give an accountof symptoms of plantdisease with suitable examples., Q.4- Give an account of the techniques used in plant breeding for disease resistance., Q.5-What is parasitism? Give a broad outline of physiology of parasitism., Q.6- Discuss theroleofenzymesandtoxinsindevelopmentofplantdisease., Q.7- Discuss thestructuralandbiochemicallinesofdefense inplantsagainst pathogens., Q.8-The cuticle acts as a physical or chemical barrier to infection. Comment upon the, statement., Q.9-Distinguish between penetration and infection., Q.10-Write notes on:, (i)-Biological inhibition of germination of spores of fungal pathogens., (ii)- Tissue culture techniques in disease resistance., (iii)- Phytoalexins., (iv)- Disease resistance., , UTTARAKHAND OPEN UNIVERSITY, , Page 230
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-10-SYMPTOMS, MORPHOLOGY OF THE, CAUSAL ORGANISM, DISEASES CYCLE AND, CONTROL MEASURES-I, 10.1- Objectives, 10.2-Introduction, 10.3-Mosaic diseases of tobacco, 10.3.1-Symptoms, 10.3.2-Morphology of the causal organism, 10.3.3-Disease cycle, 10.3.4-Control measures, 10.4-Citrus canker, 10.4.1- Symptoms, 10.4.2- Morphology of the causal organism, 10.4.3-Disease cycle, 10.4.4-Control measures, 10.5-Wart diseases of potato, 10.5.1- Symptoms, 10.5.2-Morphology of the causal organism, 10.5.3-Disease cycle, 10.5.4-Control measures, 10.6-Early blight of potato, 10.6.1- Symptoms, 10.6.2-Morphology of the causal organism, 10.6.3-Disease cycle, 10.6.4-Control measures, 10.7-Summary, 10.8- Glossary, 10.9- Self assessment question, 10.10-References, 10.11-Suggested Readings, 10.12-Terminal Questions, UTTARAKHAND OPEN UNIVERSITY, , Page 231
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 10.1- OBJECTIVES, After reading this unit student will be able:, , , , , To study the morphology of the causal organism of the diseases., To get an idea of etiology or disease cycle of the causal organism of the disease and, To know the control measures or the management of disease., , 10.2-INTRODUCTION, Globally, enormous losses of the crops are caused by the plant diseases. The loss can occur, from the time of seed sowing in the field to harvesting and storage. Important historical, evidences of plant disease epidemics are Irish Famine due to late blight of potato (Ireland,, 1845), Bengal famine due to brown spot of rice (India, 1942) and Coffee rust (Sri Lanka,, 1967). Such epidemics had left their effect on the economy of the affected countries. The, normal physiological functions of plants are disturbed when they are affected by pathogenic, living organisms or by some environmental factors. Initially plants react to the disease, causing agents, particularly in the site of infection. Later, the reaction becomes more, widespread and histological changes take place. Such changes are expressed as different, types of symptoms of the disease which can be visualized macroscopically. As a result of the, disease, plant growth in reduced, deformed or even the plant dies. When a plant is suffering,, we call it diseased. Thus a disease is a condition that occurs in consequence of abnormal, changes in the form, physiology, integrity or behaviour of the plant., Plant diseases are caused by pathogens. Hence a pathogen is always associated with a, disease. In other way, disease is a symptom caused by the invasion of a pathogen that is able, to survive, perpetuate and spread. Further, the word ―pathogen‖ can be broadly defined as, any agent or factor that incites 'pathos or disease in an organism or host. In strict sense, the, causes of plant diseases are grouped under following categories:, 1. Animate or biotic causes: when disease is caused by a pathogens i.e. a living, organism.Pathogens of living nature are categorized into the following groups, (i) Fungi (ii), Algae (iii) Bacteria (iv) Phanerogams (v) Phytoplasma (vi) Protozoa (vii) Rickettsia-like, organisms (viii) Nematodes, 2. Mesobiotic causes: These disease incitants are neither living nor non-living, e.g. (i), Viruses (ii) Viroides, 3. Inanimate or abiotic causes: In true sense these factors cause damages (any reduction, in the quality or quantity of yield or loss of revenue) to the plants rather than causing disease., The causes are: (i) Deficiencies or excess of nutrients (e.g. ‗Khaira‘ disease of rice due to Zn, deficiency) (ii) Light (iii) Moisture (iv) Temperature (v) Air pollutants (e.g. black tip of, mango) (vi) Lack of oxygen (e.g. hollow and black heart of potato) (vii) Toxicity of, pesticides (viii) Improper cultural practices (ix) Abnormality in soil conditions (acidity,, alkalinity)., , UTTARAKHAND OPEN UNIVERSITY, , Page 232
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Classification of plant disease, To facilitate the study of plant diseases they are needed to be grouped in some orderly, fashion. Plant diseases can be grouped in various ways based on the symptoms or signs (rust,, smut, blight etc.), nature of infection (systemic or localized), habitat of the pathogens, mode, of perpetuation and spread (soil-, seed- and air-borne etc.), affected parts of the host (aerial,, root disease etc.), types of the plants (cereals, pulses, oilseed, ornamental, vegetable, forest, diseases etc.). But the most useful classification has been made is based on the type of, pathogens that cause plant diseases. Since this type of classification indicates not only the, cause of the disease, but also the knowledge and information that suggest the probable, development and spread of disease alongwith their possible control measures. The, classification is as follows:, 1. Infectious plant diseases: a. Disease caused by parasitic organisms: These organisms, are included under animate or biotic causes incite diseases in plants. b. Diseases caused by, viruses and viroid (mesobiotic causes)., 2. Non-infectious or non-parasitic or physiological diseases: The factors included in, inanimate or abiotic causes incite such diseases in plants under a set of suitable, environmental conditions., , Symptoms of plant diseases, A visible or detectable abnormality expressed on the plant as a result of disease or disorder is, called symptom. The totality of symptoms is collectively called as syndrome while the, pathogen or its parts or products seen on the affected parts of a host plant is called sign., Different types of disease symptoms are cited below:, Necrosis: It indicates the death of cells, tissues and organs resulting from infection by, pathogen. Necrotic symptoms include spots, blights, burn, canker, streaks, stripes, dampingoff, rot etc., , Wilt: Withering and drooping of a plant starting from some leaves to growing tip occurs, suddenly or gradually. Wilting takes place due to blockage in the translocation system caused, by the pathogen., , Die-back: Drying of plant organs such as stem or branches which starts from the tip and, progresses gradually towards the main stem or trunk is called die-back or wither tip., , Mildew: White, grey or brown coloured superficial growth of the pathogen on the host, surface., Rusts: Numerous small pustules growing out through host epidermis which gives rusty (rust, formation) appearance of the affected parts., Smuts: Charcoal-like and black or purplish-black dust like masses developed on the affected, plant parts, mostly on floral organs and inflorescence., Blotch: A large area of discolouration of a leaf, fruit etc. giving a blotchy appearance., , White blisters: Numerous white coloured blister-like ruptures are surfaced on the host, epidermis that forms powdery masses of spores of fungi., UTTARAKHAND OPEN UNIVERSITY, , Page 233
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Colour change: Conversion of green pigment of leaves into other colours mostly to yellow, colour, in patches or covering the entire leaves. It happens because of the following, symptoms., , Etiolation: Yellowing due to lack of light, (ii) Chlorosis: Yellowing due to infection, viruses, bacteria, fungi, low temperature, lack of iron etc. (iii) Albino: Lack of any pigment, which causes white or bleached symptoms (iv) Chromosis: Red, purple or orange, pigmentation due to physiological reasons., , Exudation: Such symptom is commonly found in bacterial diseases when masses of, bacterial cells ooze out to the surface of affected plant parts and form some drops or smear., The exudation forms a crust on the host surface after drying., , Overgrowth: Excessive growth of the plant parts due to infection by pathogens., Overgrowth takes place by two processes (i)Hyperplasia: abnormal increase in size due to, excessively more cell division (ii)Hypertrophy: abnormal increase in size or shape due to, excessive enlargement of the size of cell of a particular tissue., , Atrophy: It is known as or dwarfing which is caused by the inhibition of growth due to, reduction in cell division or cell size., , Sclerotia: These are dark and hard structures of various shaped composed of dormant, mycelia of some fungi. Sometimes, sclerotia are developed on the affected parts of the plant., Presence of sclerotia on the host surface is specifically called a sign of disease rather than, symptom., , Plant disease management, The word ‗control‘ is a complete term and a permanent ‗control‘ of a disease is rarely, achieved whereas, ‗management‘ of a disease is a continuous process and is more practical in, influencing adverse effect caused by a disease. Disease management requires a detail, understanding of all aspects of crop production, economics, environmental, cultural, genetics, and epidemiological information upon which the management decisions are made., , A.Principles of plant disease management:, There are six basic concepts or principles or objectives lying under plant disease, management., 1. Avoidance of the pathogen: Occurrence of a disease can be avoided by, planting/sowing a crop at times when, or in areas where, inoculum remain ineffective/, inactive due to environmental conditions, or is rare or absent., 2. Exclusion of the pathogen: This can be achieved by preventing the inoculum from, entering or establishing in a field or area when it does not exist. Legislative measures like, quarantine regulations are needed to be strictly applied to prevent spread of a disease., , 3. Eradication of the pathogen: It includes reducing, inactivating, eliminating or, destroying inoculum at the source, either from a region or from an individual plant (rouging), in which it is already established., UTTARAKHAND OPEN UNIVERSITY, , Page 234
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 4. Protection of the host: Host plants can be protected by creating a toxin barrier on the, host surface by the application of chemicals., , 5. Disease resistance: Preventing infection or reducing the effect of infection of the, pathogen through the use of resistance host which is developed by genetic manipulation or by, chemotherapy., , 6. Therapy: Reducing severity of a disease in an infected individual. The first five, principles are prophylactic (preventive) procedure and the last one is curative., , B. Methods of plant disease management, 1. Avoidance of the pathogen:, i. Choice of geographical area, ii. Selection of a field, iii. Adjustment of time of sowing, iv. Use of disease escaping varieties, v. Use of pathogen-free seed and planting material, vi. Modification of cultural practices, , 2. Exclusion of inoculum of the pathogen, i. Treatment of seed and plating materials, ii. Inspection and certification, iii. Quarantine regulations, iv. Eradication of insect vector, , 3. Eradication of the pathogen, i. Biological control of plant pathogens, ii. Eradication of alternate and collateral hosts, iii. Cultural methods:, a. Crop rotation, b. Sanitation of field by destroying/burning crop debris, c. Removal and destruction of diseased plants or plant parts, d. Rouging, iv. Heat and chemical treatment of diseased plants, v. Soil treatment: by use of chemicals, heat energy, flooding and fallowing, , 4. Protection of the host, i. Chemical control: application of chemicals (fungicides, antibiotics) by seed, treatment, dusting and spraying, ii. Chemical control of insect vectors, iii. Modifications of environment, iv. Modification of host nutrition, , UTTARAKHAND OPEN UNIVERSITY, , Page 235
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 5. Disease resistance/Use of resistant varieties: Development of resistance in host is, done by, i. Selection and hybridization for disease resistance, ii. Chemotherapy, iii. Host nutrition, iv. Genetic engineering, tissue culture, , 6. Therapy: Therapy of diseased plants can be done by, i. Chemotherapy, ii. Heat therapy, iii. Tree-surgery, , 10.3-MOSAIC DISEASE ON TOBACCO, This plant disease is caused by Tobacco Mosaic Virus (TMV). it is known to occur in all, tobacco growing countriesof the world. It was first described in detail by Adolph Mayerin, 1886. Tobacco Mosaic Virus speciallyinfectstobacco and members of family Solanaceae. The, virus may affect more than 150 genera of herbaceous dicotyledonous plants including many, vegetables, flowers and weeds., , Fig. 10.1 Tobacco leaf showing the mosaic symptoms, , 10.3.1-Symptoms, It produce mosaic* like symptoms on plants. The symptoms on the healthy plant appear after, ten days of infection. The first symptom is light green coloration between the veins of the, young leaves. This is quickly followed by the development of mosaic or mottled pattern of, light abd dark green areas in the leaves (Fig.10.1). In infected plants, the leaves become, small, curled and puckered. Symptoms on plants includechlorosis, curling, mottling,, dwarfing, distortion and blistering of leaves. Mosaic does not result in plant death, but if, infection occurs early in the season, plants are stunted., , 10.3.2-Morphology of the causal organism, It is the first virus to be discovered by Iwanowski in 1892. It is a rod shaped virus., The virion measures 18×300 nanometers and weighs 39 million Daltons. The capsid is made, , UTTARAKHAND OPEN UNIVERSITY, , Page 236
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , from 2130 protein subunits (each subunit consists of 158 aminoacids) and one molecule of, genomic single stranded RNA. The ssRNA consists of 6,400 nucleotides., , 10.3.3-Disease cycle, It is the most persistent plant virus. It has been known to survive 50 years in dried, plant parts. The most common sources of virus inoculum for TMV are the debris of infected, plants that remain in the soil and certain infected tobacco products which contaminate, workers hand. It is also transmitted mechanically by vegetative propagation of plants,, grafting, seeds, pollens and by being carried on the mouth parts of chewing insects., Once the virus enters the host, it begins to multiply by inducing cells to form new, virus. It takes over the metabolic cell processes resulting in abnormal cell function. Its RNA, directs the synthesis of viral protein. After the RNA and the protein is produced, they, undergo self assembly. After the assembly, they are released outside the cell after its lysis., , 10.3.4-Control measures, There are no known chemicaltreatments used under field conditions that eliminate viral, infection from plant tissues once it occurs. However, some important control measures to, check the infection are:, Discarding infected plants., Growing virus free plants., Propagate plants via seeds rather than vegetatively., Crop rotation., Growing of resistant strains., Removing of all weeds during and after the growing season., Disinfecting tools by placing them in boiling water for 5 minutes and washing with a, strong soap or detergent solution., Discouraging use of tobacco by workers., Encouraging the practice of washing hands by workers with soap and water before, and after handling plants., *Mosaic: A viral disease in plants that causes yellow patches to develop on the leaves, giving these a variegated, appearance. Variegation is the occurrence of different coloured patches, spots or streaks in plant leaves, petals or, other parts, due to absence of pigments or different combination of pigments in the affected area of the leaf., Variegation may be brought about by infection for e.g., TMV infection., , 10.4 CITRUS CANKER, Fawcett and Jenkins (1933) reported that citrus canker disease is originated in India and, Java because they had detected canker lesions on the oldest citrus herbaria kept at Royal, Botanical Gardens in Kew, England (Citrus medica collected in India between 1827-1831,, Citrus aurantifolia collected in Java between 1842-1844). Now the disease known to occurs, almost in all citrus growing countries of the world. This disease affects cultivars and hybrids, UTTARAKHAND OPEN UNIVERSITY, , Page 237
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , of citrus and citrus relatives including orange, grapewine,mandarin, lemon, lime, tangerine,, sour orange and roughlemon. Because of its rapid spread, high potential damage and impact, on export and domestic sales, the disease is a significant threat to all citrus growing countries., , Fig.10.2. Fruits leaves and stem showing Citrus canker, , 10.4.1- Symptoms, Plants infected with citrus canker disease have characteristic lesions on leaves, stems, and fruits with raised brown, water soaked margins which develop around the necrotic tissues, (Fig.10.2). A characteristic symptom of the disease on the leaves is the yellow halo that, surrounds lesion. These lesions start as pin point spots and attain a maximum size of 2-10mm, diameter. Lesions become visible about 7-10 days after infection on the lower surface. The, lesion persists on twigs and branches for several years and support long term survival of the, bacterium. Severely infected fruits can drop prematurely, leading to reduced yield. The, internal quality of mature fruit with lesions is unaffected and is still edible and usable for, juice., , 10.4.2- Morphology of the causal organism, (Xanthomonas axonopodispv. Citri andXanthomonas axonopoidspv.aurantiofolli.), Xanthomonasis small aerobic, rod shaped motile bacterium. It is 5.20×0.5-0.75 micron in size, and has single polar flagellum. It formschains and capsules but no spores., , 10.4.3-Disease cycle, Infected twigs having old lesions are the main source of infection. These lesions ooze, bacteria which are blownaway by the wind or dispersed by rain.Healthy plants are infected by, these bacteria which entered through stomata or wounds (caused by citrus leaf, minorphyllocnistiscitrellain feeding activity).The bacteria after penetration in to host multiply, in the intercellular spaces, dissolve the middle lamella and get established in to the, cortex.Lesions on healthy plants become visible about 7 to 10 days after infection on the, underside of the leaves and soon thereafter on the upper surface. Man is also an important, agent of dissemination through infected nursery stock. High mean temperature (2030)coincide with high rain fall favours the development of disease., , UTTARAKHAND OPEN UNIVERSITY, , Page 238
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 10.4.4-Control measures, , , , , , , , , , Eradication of infected trees and burning them., Applying preventive sprays of copper based Kocide 3000., Pruningof infected twigs and leaves during the dry seasonand then spraying the trees, with 1% Bordeaux mixture., Spraying the antibiotics e.g. streptomycin sulphate and phonomycin., Strictly applying quarantine methods., Replacing susceptible citrus cultivars with resistant cultivars., Growing winds breaks to hinder inoculum dispersal., Devloping transgenic plants for e.g.Xanthomonasresistance gene from the rice has, been transferred in to sweet orange., , 10.5 WART DISEASES OF POTATO, Potato wart is an important and serious disease of cultivated potato (Solanum tuberosum), with numerous accounts of disease detections occurring worldwide. Potato wart is known by, various names, including black scab, black wart, cauliflower disease, potato tumor, potato, cancer, potato canker, wart, warty disease, and certainly many other descriptive names in, several languages. The disease is caused by the fungus Synchytrium endobioticum. This, organism is considered to be the most important world-wide plant pathogen of cultivated, potato. S. endobiotocum is a primitive fungus characterized by the lack of hyphae, the, formation of zoospores and thedevelopment of long-lived resting sporangia. This fungus, invades certain meristematic tissues of the potato plant. This can preclude plant emergence, when sprout tips are infected. After plant emergence, when stolon tips or tuber eyes become, infected, resultant disease processes can render the potato tuber unrecognizable and unfit for, human consumption. The potato wart fungus is not a human pathogen and poses no threat to, human health. This pathogen is readily distributed via movement of infested soil and by, infected seed tubers. Because of the great potential for disease loss, any degree of infestation, or indication of potato wart universally (world-wide) results in strict quarantine and other, regulatory measures designed to confine the known infestation and to preclude pathogen redistribution. Although direct losses from potato wart may be insignificant when first detected,, indirect economic losses resulting from zero-tolerance regulations for potato wart can be, devastating to the people. Indirect economic losses become especially evident in situations, where seed tuber production areas become subject to quarantine measures, as well as when, the movement of commercial potatoes is restricted. For example, a well-documented, detection of potato wart on Prince Edward Island (Canada) late in the year 2000 growing, season and the ramifications of subsequent regulatory actions resulted in an estimated $30, million loss to the Island‘s economy in that first year alone., , UTTARAKHAND OPEN UNIVERSITY, , Page 239
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.10.3: Potato tubers showing wart disease, , 10.5.1- Symptoms, The diagnostic symptoms of potato wart are galls produced on several plant parts., These galls are primarily parenchymatous and may form on stem tissue, including the stem, base, stolon buds, and tuber eyes (Fig.10.3). Galls most often form on below-ground portions, of the plant, and the presence of the disease is typically not noticed until tubers are lifted, during harvest. However, galls also occasionally form on the upper stem, leaf, or flower., Galls vary in shape but are mostly spherical outgrowths, ranging from 1 to 8 cm (0.4 to 3.2, inches) or more in diameter, but may become fist-sized in some instances. Aboveground galls, are green to brown, turning black at maturity, and are prone to decay. Belowground galls are, white to brown and turn black as they decay. Tubers may be disfigured or become almost, unrecognizable when they are infected early in development and replaced by galls. Galls, present on tubers at harvest may become desiccated and barely noticeable or, alternatively,, the galls may decay. Because the disease can continue developing during storage, desiccated, galls barely noticed at harvest may become increasingly evident during prolonged storage., Although potato wart does not kill the host, the meristematic tissue of sprouts may be so, severely attacked that plants ultimately fail to emerge from seed tubers early in the growing, season. Also, infected plants may develop general symptoms of reduced vigor, especially in, association with the formation of small greenish-yellow warty growths at the stem base. The, true potato roots are not known to be infected., , 10.5.2-Morphology of the causal organism, The fungus (Synchytrium endobioticum Schilberszky) does not produce hyphae and is, an obligate, holocarpic, endobiotic parasite. It is a long-cycled chytrid characterized by a, short-lived swarm (summer) sporangial stage resulting from host infection by uniflagellate, zoospores and a resting (winter) sporangial stage. Both sporangial types germinate to release, 200-300 zoospores, which are pear-shaped infective units (1.5 to 2.2 µm in diameter) and, motile by means of a posterior flagellum. Resting sporangia are golden brown and spheroidal, (35 to 80 µm in diameter). The resting sporangium wall has prominent exterior ridges and, contains chitin fibrils., , UTTARAKHAND OPEN UNIVERSITY, , Page 240
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 10.5.3-Disease cycle, In the spring, resting sporangia in decaying warts and soil germinate to release, haploid (uninucleate) zoospores. These zoospores migrate in soil water for a limited distance, (50 mm or less) with the help of single flagellum to arrive at epidermal cells of meristematic, tissues of growing points, (buds, stolon tips, or young leaf primordial). Zoospores are shortlived. They loose flagellum, become encysted and infect susceptible host tissue within 1-2 hr, after their formation. Potato host cells become greatly enlarged. Haploid soriare formed, inside the host cells while neighboring host cells begin to proliferate, resulting in the, characteristic warty galls and the increased presence of the meristematic tissue. This provides, new infection courts for the fungus. Each sorus contains one to nine summer sporangia,, which in turn germinate to produce new haploid zoospores. These zoospores again infect, susceptible tissue (i.e., a secondary disease cycle). These rapidly repeating secondary disease, cycles ultimately result in an extensive invasion of host cells and rapid onset of gall, formation. Young galls are nutrient sinks and expand rapidly at the expense of other plant, tissue. For example, gall volume has been observed to increase more than 1,800-fold in 16, days., Under conditions of stress, such as water shortage, zoospores may also conjugate (fuse) in, pairs to form uninucleate, diploid, biflagellate zygotes which infect the host tissue to form, resting sporangia. Following infection by zygotes, the host cell in which resting sporangia, form does not swell but divides to form galls. The host cell wall remains closely attached and, forms an outer layer to the resistant, thick-walled resting (winter) sporangium. As these galls, decay and disintegrate, they release the thick-walled resting sporangia into the soil, environment. Resting sporangia are endogenously dormant and can remain viable for 40 to 50, years at depths of up to 50 cm (20 inches) in the soil profile., The resting sporangia are primarily spread in infected seed tubers, which may have incipient, warts that pass undetected, or in infested soil adhering to tubers, equipment, and by other, carriers of contaminated soil. Resting sporangia survive even in passage through the digestive, system of animals which fed on infected potatoes, and contaminated manure also can disperse, inoculum. Earthworms have also been found to serve as means of inoculum dispersal., Resting sporangia can also be dispersed by wind-blown soil or by flowing surface water. The, zoospores are too short-lived to significantly contribute to inter-field dispersal of the potato, wart pathogen. Most potato wart diseases have been recorded in small garden plots where, there has been repeated culture of susceptible potato hosts., Under ideal conditions, potato wart can develop when the inoculum density is less than one, resting spore per gram of soil. Potato wart is favored by cool, wet soils during tuber, development. A soil temperature of at least 8°C (46°F) and water is required for the, germination of both winter and summer sporangia and for the dispersal of zoospores. Cool, summers with average temperatures of 18°C (64°F) or less, and annual precipitation of 70 cm, (28 inches) are important for the development of the disease. Soil pH is of less importance;, the disease has been found to occur in plants growing in soils ranging from pH 3.9 to pH 8.5., Temperatures of 12 to 24°C (54 to 75°F) favor infection., , UTTARAKHAND OPEN UNIVERSITY, , Page 241
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 10.5.4-Control measures, , , , Wart affected tubers should not be planted., Wart resistant varieties like KufriKanchan, KufriJyoti should be grown., , 10.6-EARLY BLIGHT OF POTATO, Alternaria solani is a fungal pathogen, which produces a disease in potato plants called early, blight (Fig.10.4). The pathogen produces distinctive "bullseye" patterned leaf spots and can, also cause stem lesions and fruit rot on tomato and tuber blight on potato. Despite the name, "early," foliar symptoms usually occur on older leaves. Distinguishing symptoms of A., solani include leaf spot and defoliation, which are most pronounced in the lower canopy., , Fig. 10.4: Leaf showing blight disease, , 10.6.1- Symptoms, In potato, primary damage by A. solani is attributed to premature defoliation of potato, plants, which results in tuber yield reduction. Initial infection occurs on older leaves, with, concentric dark brown spots developing mainly in the leaf center. The disease progresses, during the period of potato vegetation, and infected leaves turn yellow and either dry out or, fall off the stem. On stems, spots are gaunt with no clear contours (as compared to leaf spots)., Tuber lesions are dry, dark and pressed into the tuber surface, with the underlying flesh, turning dry, leathery and brown. During storage, tuber lesions may enlarge and tubers may, become shriveled. Disease severity due to A. solani is highest when potato plants are injured,, under stress if they lack proper nutrition., , 10.6.2-Morphology of the causal organism, A. solani belongs to Fungi-imperfectii. Colony morphology of A. solani varies widely,, but is generally effuse, greyish brown to black, with a cotton-felt, or velvet-like texture., Growth is rapid on many growth media, but special conditions are required for sporulation., Orange to dark red pigments are produced by the fungus which colour the medium. Cells of, A. solani are multinucleate, but different organs vary in the number of nuclei. Nuclear, division in hyphal cells is followed by multiple septation, which results in the division of, elongated tip cells into several multinucleate cells. Conidiophores are dark or olivaceous, brown, thick-walled, straight to flexuous, septate, and arise singly or in small groups, up to, UTTARAKHAND OPEN UNIVERSITY, , Page 242
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 110 µm in length and 6–10 µm in diameter. Conidia are usually pale to olivaceous-brown,, produced singly or seldom in short chains, straight or slightly flexuous, obclavate to elongate,, double walled with 0–8 longitudinal or oblique and 6–19 transverse septa, 75–350 µm in, length and 20–30 µm in diameter in the broadest part. Beaks are about one-half to one-third, the length of the conidium, filiform, straight,septate, hyaline to pale brown and 5–9 µm in, diameter. Because of the variability in spore dimensions, they overlap with dimensions of, other large sporedAlternaria species. In routine work, identification is assisted by leaf, symptoms, host range and cultural characteristics., , 10.6.3-Disease cycle, Alternaria solani belongs to Deuteromycetes and shows a polycyclic life cycle. The, fungus reproduces aesexually by means of conidia. The life cycle starts with the fungus, overwintering in crop residues or wild members of the Solanaceae family, such as Black, nightshade. In the spring, conidia are produced. Multicellular conidia are splashed by water, or by wind onto an uninfected plant. They infect the plant by entering through small, wounds, stomata, or direct penetration. Infections usually start on older leaves close to the, ground. The fungus takes time to grow and eventually forms a lesion. From this lesion, more, conidia are created and released. These conidia infect other plants or other parts of the same, plant in the same growing season. Every part of the plant can be infected and form lesions., This is especially important when fruit or tubers are infected as they can be used to spread the, disease., In general, development of the pathogen can be aggravated by an increase in inoculum from, alternative hosts such as weeds or other solanaceous species. Disease severity and prevalence, is highest when plants are mature., , 10.6.4-Control measures, Cultural control, , , , Clear infected debris from field to reduce inoculum for the next year., Water the plants in the morning that so plants are wet for the shortest amount of time., , , , Use a drip irrigation system to minimize leaf wetness which provides optimal conditions, for fungal growth., , , , Use mulch so that spores in soil cannot splash onto leaves from the soil., , , , Rotate to a non-Solanaceous crop for at least three years., , , , If possible, control wild population of Solanaceae. This will decrease the amount of, inoculum to infect new plants., , , , Closely monitor field, especially in warm damp weather when it grows fastest, to reduce, loss of crop and spray fungicide in time., , , , Use plant resistant cultivars., , UTTARAKHAND OPEN UNIVERSITY, , Page 243
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , BSCBO-101, , Increase air circulation in rows. Damp conditions allow for optimal growth of A., Solani and the disease spreads more rapidly. This can be achieved by planting farther, apart or by trimming leaves., , Chemical control, There are numerous fungicides on the market for controlling early blight. Some of the, fungicides on the market are azoxystrobin, pyraclostrobin, Bacillus subtilis, chlorothalonil,, copper products, hydrogen dioxide (Hydroperoxyl), mancozeb, potassium bicarbonate, and, ziram. Specific spraying regiments are found on the label. Labels for these products should be, read carefully before applying., , 10.7 SUMMARY, Disease is a condition that occurs in consequence of abnormal changes in the form,, physiology, integrity or behaviour of the plant. Plant diseases are caused by pathogens. Hence, a pathogen is always associated with a disease. The disease is caused by bacteria, fungi,, viruses and nematodes e.g., Citrus canker, Blight and wart disease of potato, mosaic disease, of tobacco etc. They show various types of symptoms or sign on the plant leaves, twigs,, flower and fruits. These diseases can be controlled biologically or chemically., , 10.8 GLOSSARY, Biotroph: A plant pathogenic fungus that requires living host cells i.e. an obligate parasite., Pathogenicity: The relative capability of a pathogen to cause disease., Deficiency: Abnormality or disease caused by the lack or subnormal level of availability of, one or more essential nutrient elements., Disease cycle: The chain of events involved in disease development., Disease: Any deviation in the general health, or physiology or function of plant or plant parts,, is recognized as a disease., Infection: The initiation and establishment of a parasite within a host plant., Inoculum: The portion of pathogen which is transferred to the host plant and cause disease., Incubation period: The period between penetration of a pathogen to the host and the first, appearance of symptoms on the plant., Parasite: An organism living upon or in another living organism (the host) and obtaining the, food from the invading host., Pathogen: An entity, usually a micro-organism that can cause the disease., Pathogenesis: It is a process caused by an infectious agent (pathogen) when it comes in, contact with a susceptible host., Primary infection: The first infection of a plant by the over wintering or over summering of, the pathogen., Symptoms: The external and internal reaction or alterations of a plant as a result of disease., Virulence: The degree of infectivity of a given pathogen., , UTTARAKHAND OPEN UNIVERSITY, , Page 244
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 10.9 SELF ASSESSMENT QUESTION, 10.9.1: Fill in the blanks1. TMV was first discovered by……………………………, 2. Inhibition of growth due to reduction in cell division or cell size is called………………., 3. Wart disease of Potato is caused by………………………., 4………………is a condition that occurs in consequence of abnormal changes in the form,, physiology, integrity or behaviour of the plant., 5. Plant pathology is the study and control of………. and…………that cause diseases., 6. The chain of events involved in disease development…………………………., , 10.9.2: Choose the correct answer from the given below:, 1. The Irish potato famine occurred in North Europe during 1845 was caused by:, (a) Alternaria solani, (b) Phytophthora infestans, (c) Synchytrium endobioticum, (d) Erwinia carotovora, 2. Which of the following combination of factors are responsible for a disease, its study and, control?, (a) Abiotic and environmental factors., (b) Biotic and abiotic factors., (c) Pathogens and environmental factors., (d) Answers b and c are true., 3. Early blight of Potato is caused by:, (a) Alternariasolani, (c) Synchytriumendobioticum, , (b)Phytophthorainfestans, (d) Solanum virus-14, , 4. Symptoms (but not signs) of a disease include:, (a) Galls produced by parasitic wasps., (b) The powdery substance on lilac leaves infected with powdery mildew., (c) Wilt., (d) Both a and c are correct., ANSWER Keys:, 10.9.1: Fill in the blanks: 1. Iwanowski, 2. Atrophy, 3. Synchytriumendobioticum, 4., Disease, 5. disease and pathogen, 6. disease cycle, , 10.9.2: Choose the correct answer from the given below:, 1. (b), 2. (b), 3. (a), 4, (d), , 10.10 REFERENCES, , UTTARAKHAND OPEN UNIVERSITY, , Page 245
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , BSCBO-101, , Introductory Plant Pathology Dr. D.V. Singh Ex-Head and Emeritus Scientist Division of, Plant Pathology Indian Agricultural Research Institute New Delhi-110012, Ellis, 1971.Dematiaceoushyphomycetes. Kew Surrey, pp692., http//www.wikispeciesfungi.org, , 10.11 SUGGESTED READINGS, , , Alexopoulus, C.J., Mims, C.W. and Blackwell, M. 1996. Introductory Mycology. John, Willey &Sons Inc., , , , Singh V, Pandey PC and Jain DK. 2005.A Text Book of Botany, Rastogi Publ. Meerut., , , , Vashista BR. 2007.A Text Book of Fungi S.Chand& Co. New Delhi., , 10.12 TERMINAL QUESTIONS, Q.1-What do you mean by a disease? Write symptoms, causal organism and control measures, of any fungal disease studied by you., Q.2-Write causal organism, symptoms, disease cycle and control measures of Early blight of, potato., Q.3-Write short notes on:, 1-Wilt symptoms., 2-Hypertrophy., 3-Hyperplasia., 4-Necrosis., , UTTARAKHAND OPEN UNIVERSITY, , Page 246
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-11- SYMPTOMS, MORPHOLOGY OF THE, CAUSAL ORGANISM, DISEASES CYCLE AND, CONTROL MEASURES-II, 11.1- Objectives, 11.2-Introduction, 11.3-Late blight of potato, 11.3.1- Symptoms, 11.3.2-Morphology of the causal organism, 11.3.3-Disease cycle, 11.3.4-Control measures, 11.4-Red root of sugarcane, 11.4.1- Symptoms, 11.4.2-Morphology of the causal organism, 11.4.3-Disease cycle, 11.4.4-Control measures, 11.5-Loose smut of wheat, 11.5.1- Symptoms, 11.5.2-Morphology of the causal organism, 11.5.3-Disease cycle, 11.5.4-Control measures, 11.6- Summary, 11.7- Glossary, 11.8- Self assessment question, 11.9-References, 11.10-Suggested Readings, 11.11-Terminal Questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 247
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 11.1 OBJECTIVES, After reading this unit student will be able:, , , , , , To know the morphology of the causal organism of the diseases of Potato, Sugarcane, and Wheat., To understand the signs or symptoms associated with the disease., To learn etiology or disease cycle of the causal organism of the disease., To study the control measures or the management of disease., , 11.2 INTRODUCTION, Fungi are a group of such plants which lack root system and chlorophyll. Hence, they lack the, capacity of mineral absorption and photosynthesis. They obtain their nutrition from other, living or dead plants and animals. Most fungi are saprophytic, i.e., they obtain their nutrition, from dead organic matter. There are certain fungi which obtain their nutrition from living, cells. These are known as parasitic fungi. These fungi also affect the physiological processes, of the host. The toxins produced by certain fungi cause morphological deformity in the host., Such effects of the parasite appear in the host plant in the form of disease symptoms.The late, blight epidemics of the 1840s triggered the Irish potato famine, but the history of the potato, as a food crop is much older. The potato (Solanum tuberosum) originated in the highlands of, the Andes in the Lake Titicaca area between Bolivia and Peru, where native people had, selected hundreds of different cultivars for centuries. Most scientists agree that Phytophtora, infestans originated in Mexico where both mating types of the fungus are commonplace., Where and how the plant and the pathogen first came together is not certain, but late blight, epidemics seem to be described in the northeastern U.S. in about 1843 and Europe in 1845., Potato crops failed for a number of years during the cool and rainy "hungry '40s." Although, poor people who were dependent on potatoes for food suffered in many areas, the disaster, was greatest in Ireland. One and one-half million people starved and a similar number, emigrated during the famine, resulting in a large Irish diaspora in many parts of North, America. As with many famines, politics enhanced the suffering. Many Irish peasants grew, cereal crops to pay their rent. Although the grain was harvested, it could not be eaten, and, was exported to the English landlords throughout the famine. In the 1990s, many exhibits and, gatherings in North America and Ireland commemorated the 150th anniversary of the famine., One reason that the early history of late blight is unclear is that the germ theory of disease, had not yet been accepted. Many preliminary studies of various plant diseases had been, conducted, but Anton de Bary's (the "father of plant pathology") conclusive studies finally, convinced the scientific community that the white sporulation of P. infestans on infected, plants was the causal agent of the disease and not the result of spontaneous generation from, the decaying vegetation. Thus, late blight signifies the official beginning of the science of, plant pathology. These early studies also contributed to Louis Pasteur's germ theory which, was proposed 15 years later. Red rot is one of the major constraints in the profitable, cultivation of sugarcane in many states of India. Except Maharashtra, the disease has been, UTTARAKHAND OPEN UNIVERSITY, , Page 248
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , recorded in all the states. This disease drastically retards the yield and considerably, deteriorates the juice quantity and quality thus hitting both the cane growers and millers., Many good varieties have gone out of cultivation due to red rot. Loose smut of wheat is a, common disease throughout the wheat-growing regions of the world. The mycelium remains, dormant in the embryo, and developing kernels are replaced by black teliospores. No seeds, develop in infected heads. The disease is spread by windblown teliospores. Cool, humid, weather favors the development of this disease. Some of the important fungal diseases of, plants are discussed in this chapter., , 11.3 LATE BLIGHT OF POTATO, The late blight is one of the destructive diseases of potato. It is the most serious of all the, potato diseases when conditions are favourable for its spread. The famous Irish famine of, 1845-46 was due largely to the failure of potato crop due to late blight infection. In India, the, disease was first introduced into the Nilgiri hills between 1870 and 1880 and very soon, it, spread to Darjeeling in the Himalayan ranges. The first severe outbreaks of the disease were, reported between 1912 and 1928 from Assam, Bengal and Bihar. In northern India, the, disease was first reported from the plains of western U.P. Since then, the disease appears as a, regular feature in the plains causing severe losses to the potato crop., , Fig.11.1. Leaves, stems and tuber showing late blight symptoms, , 11.3.1- Symptoms, The symptoms of the disease can be seen on any part of the plant, viz., leaves,, petioles, stems and tubers (Fig.11.1). On the leaves, the symptoms appear in the form of dark, brown, oval or irregular water soaked areas. In the early stages, the symptoms develop at the, tips or the margins of the old leaves. The infection spreads vigorously when temperature is, low and atmosphere is humid, and soon appears in the form of blight. In case of severe, infection,practically all the parts of the host become brown and then degenerate. After the, tops have been blighted, the infection reaches to the underground tubers. In the infected, tubers, the skin becomes slightly sunken and dark in colour. If conditions are humid, the cells, of the tuber become soft and dark brown. This symptom is known as wet rot. In dry, , UTTARAKHAND OPEN UNIVERSITY, , Page 249
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , atmosphere, however, the potato pulp does not rot but its anterior part becomes black. This, condition is called dry rot., , 11.3.2-Morphology of the causal organism, The disease is caused by Phytophthora infestans. The mycelium is endophytic, consisting of hyaline, profusely branched coenocytic hyphae. The hyphae develop, intercellularly and form haustoria. Ovoid or lemon-shaped sporangia are produced on, sporangiophores. The sporangia are at first terminal but become lateral due to sympodial, branching of the sporangiophore. The sporangium may germinate directly, forming a germ, tube at the apex or its protoplasmic contents divide to form a number of biflagellate, zoospores which emerge through the papilla. The method of germination is much governed, by temperature; low temperature favours zoospores formation, whereas higher temperature is, responsible for the germ tube development. Sexual reproduction is oogamous type. The, antheridium is somewhat elongated and amphigynous, whereas the oogonium is pear-shaped, to almost spherical, smooth and reddish brown in colour. The fusion of egg and male nucleus, results in the formation of a diploid oospore. The oospore germinates by producing a germ, tube and the tip of which tube ultimately develops in to a sporangium., , 11.3.3-Disease cycle, The infected tubers are the main source of infection. Thedormant mycelium in the, tubers becomes active and grows upward in the stem and sporulates on small shoots., Epiphytotics of the disease are likely to occur when unusually cool weather combined with, abundant moisture prevails at the time the sporangia are being produced. The optimum, temperature for the sporulation is 21˚C. The sporangia germinate giving rise to zoospores at, 12˚C and by germ tube, 21˚C. 100 percent relative humidity causes abundant production of, sporangia. Sporangia are easily detached and disseminated by rain or air. On reaching a, suitable host, the sporangia germinate either by germ tubes or by zoospores depending upon, the environmental conditions. The spores from the blighted leaves are washed down into the, soil where they penetrate to different depths reaching the healthy tubers. Contact of healthy, tubers with diseased leaves at the harvesting time is another source of tuber infection, (Fig.11.2)., Several theories have been put forth to explain the yearly occurrence of late blight; but (i), persistence of mycelium in the affected tubers, and (ii) survival of fungus in the fruiting stage, or as dormant mycelium in the tubers left in the field from the preceding crop, constituting, the primary inoculum are the most accepted ones. In Indian climatic conditions, the, possibility of survival of the pathogen through soil in any form is very remote. Thus, it seems, the infected seed tubers are responsible for the spread of the disease., , UTTARAKHAND OPEN UNIVERSITY, , Page 250
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.11.2: Phytophthorainfestans causing late blight disease of Potato (Disease cycle), , 11.3.4-Control measures, The late blight can be effectively controlled by the following methods:, Healthy seed tubers., Field sanitation., Delayed harvesting and sorting potatoes from a blighted field., Tuber treatment before storage., Storage in a cool, dry and well aerated store house., Use of disease-resistant varieties, like Kufri red, Kufrineela, Kufrikundan, etc., Foliar spray of fungicides like Bordeaux mixture, Dithane Z-78, Fytolan, Blitox, etc., Good late blight management practices include disease prevention, sanitation, cultural, practices, field monitoring, an effective fungicide spray program and postharvest protection., , Sanitation, Cultural Practices and Field Monitoring, 1. Plant disease-free seed. Inspect seed potatoes within 24 hours of delivery. Cut a sample of, tubers and look for the reddish brown dry rot characteristic of late blight tuber rot., 2. Test the seed lots for late blight before planting. When purchasing seed, it is recommended, to have them tested for the absence of blighted seed by an authorized provincial service in, your region., UTTARAKHAND OPEN UNIVERSITY, , Page 251
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 3. Grade seed potatoes after being cut to remove any late blight infected tubers. Infected, tubers can be a potential source of early infections in the field., 4. Frequently disinfect seed cutting equipment., 5. Immediately after cutting, treat seed with a recommended mancozeb-based seed piece, fungicide., 6.Bury cull piles before crop emergence. Infected tubers in cull and rock dump piles are a, major source of infection for the new crop. Buried tubers may germinate and grow. Rogue or, treat volunteer plants with a herbicide. Slivers and pieces of potato remaining from cutting, operations should also be buried., 7. Volunteer potato plants can be a source of infection. Any volunteer potato plants in a field, should be removed by rouging or using herbicides. For non-seed fields where late blight is, found, consider applying a sprout inhibitor to control volunteers in the following year., 8. Controlling late blight susceptible Solanacaeous weeds such as hairy nightshade, in potato, as well as in non-potato crops is an important measure of controlling late blight incidence in, potato., 9. Immediately report any suspected incidence of late blight to your extension specialist or to, the nearest agricultural center. If late blight is identified, roguers and other workers should, wear pants and boots which can be disinfected (e.g. Bleach solution diluted 1:9 with water; or, other disinfectants) between different fields. Equipment should also be washed and, disinfected before entering adjoining fields., 10. Construction of a deep hill may help restrict spores from washing down through the soil, and infecting the developing tubers., 11. Weather conditions favorable for late blight development can be determined using late, blight forecasting models that use relative humidity, rainfall and temperature data. The, weather data is converted into units called "severity values" for the purpose of predicting late, blight outbreaks. Consult your extension specialist for information on late blight forecasts for, your area., 12. Monitor your crop. Scout fields with special attention to low spots and along tree edges, where moisture persists after rains or dews. Have a good look at stems and leaves for late, blight symptoms. Stem infections will be diminished during dry periods but will be reactivated in humid weather., 13. When late blight is first identified, top kill or rogue an area twice the size of the infected, area. All rogued infected plants should be put in plastic bags and then taken out of the field., 14. Rolling or rotobeating a crop before top killing would expose the soil and lower canopy, to drying. Rolling also seals cracks in the soil and may reduce tuber infections., 15. Top kill at least 2 weeks prior to harvest to allow time for infected tubers to rot and to, promote tuber maturity and thicker skins at harvest. Vines should be completely dead at, harvest. 16. Late blight causing spores survive longer in wet soils. Harvest when the soil, surface is dry or wind row the potatoes and allow the surface of tubers to dry before harvest., UTTARAKHAND OPEN UNIVERSITY, , Page 252
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 17. Dig potential problem areas such as sprayer rows and low areas last and store these, potatoes where they can be easily moved out in case of a problem., 18. Wet or bruised tubers are more likely to get infected with late blight. Skinned or cut and, bruised areas are direct entry points for late blight and other diseases. However, wound is not, always a requirement to occur an infection on wet tubers., 19. Grade out any obviously diseased potatoes before they are put into storage., 20. If late blight is seen on the foliage, there will also likely be tuber infections. Immediately, following harvest, these tubers should be ventilated with a high volume of air at low humidity, until the surface of the potatoes is dry. This may lead to higher shrinkage than normal, but, losses due to storage rots will be reduced., 21. Potato lots with 5% or more late blight infections (by weight) should be stored in the front, of the storage or in separate bins, so they can be easily removed in a high risk situation., 22. Postharvest treatment with fungicides containing phosphorous acid will protect healthy, tubers from pink rot or late blight infections occurring at harvest. Ensure even coverage with, the fungicide. Follow label rate and recommendations., , Fungicide Spray Programme:, A preventive spray program is always recommended. Effective control by fungicides requires, good coverage of the foliage, proper rates and timing of applications. Generally, fungicides, are most effective in the early stages of infections before symptoms appear. However, no, fungicide can cure an established infection. Fungicides against late blight are essentially, protectants and not particularly persistent. They must be used to protect plants as prophylactic, sprays in routine programmes, in an overall strategy designed to prevent the disease infecting, the crop., Contact fungicides retain on the surface of the plant where these are applied and only protect, the plant where the spray is deposited or subsequently re-distributed by moisture. Contact, fungicides are not taken into the plant and therefore are vulnerable to erosion by wind, rain, and degradation by sunlight. They do not protect new plant growth formed after the spray has, been applied. These fungicides have no effect against already established late blight, infections., Translaminar fungicides are absorbed by the leaves and show limited redistribution from, upper sprayed surface to lower unsprayed surface. They are generally more rainfast than, contact fungicides, but do not move within the plant to protect the new growth., Systemic fungicides are absorbed into plant tissue and may offer some after-infection, activity. Very few fungicides are truly systemic (i.e., move freely throughout the plant);, however, some are upwardly systemic (i.e., move only upward in the plant through xylem, tissue), and some are locally systemic (i.e., move into treated leaves and redistribute to some, degree within the treated area of the plant., , UTTARAKHAND OPEN UNIVERSITY, , Page 253
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 11.4 RED ROT OF SUGARCANE, Red rot of sugarcane is a serious disease prevalent wherever sugarcane is grown in the, world. The disease was first described in Java in 1893 under the name red smut. In 1906,, Butler reported the disease symptoms in several cane varieties in India and renamed it as red, rot. Serious Epiphytotics of this disease have occurred in Northern India (U.P., and Bihar, during 1939-40 and 1946-47). However, localized epidemics occur almost every year., , 11.4.1- Symptoms, The disease appears on all aerial parts of the plant. The early symptoms of the disease, are yellowing and drooping of leaves. The stems show little indication of the disease in early, stages but as severity of the disease increases the cane splits lengthwise and subsequently red, blotchesappear throughout the length of the cane. These blotches emit a peculiar smell of, alcohol fermentation. The reddening appears mainly in the vascular region. Ultimately, the, cane becomes dull in appearance, get rotten and shrinks at the internodes. Besides, the, conspicuous symptoms also appear on the leaves. On the mid-ribs of leaves, infection, originates as a dark reddish area which elongates rapidly, forming blood-red lesions with dark, margins. In later conditions, the centre of the lesions becomes straw coloured (Fig. 3)., , Fig. 11.3: Yellowing and drooping of leaves and reddening of stems shows the Red rot disease in, Sugarcane, , 11.4.2-Morphology of the causal organism, The red rot of sugarcane is caused by Colletotricum falcatum. The perfect stage of, this fungus has been described in Ascomycetes as Glomerella tucumanensis. The mycelium, is inter-or intracellular, profusely branched, septate and contains characteristic oil droplets. In, later stages the hyphae closely interwine with one another and form small stromata under the, host epidermis. The fungus reproduces asexually by the formation of conidia developed in, acervuli. The conidiophores are usually aseptate, unbranched and are arranged compactly like, palisade tissue. Usually a single conidium develops at the tip of each conidiophore but, occasionally the conidia are produced in acrogenous chains. The conidia are hyaline, crescent, or sickle-shaped. An oil drop is present in the centre of each conidium. The conidia germinate, by producing 1 to 4 germ tubes and form the new mycelium., , UTTARAKHAND OPEN UNIVERSITY, , Page 254
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Perithecia are globose and are produced on the various part of the host, and measure, 150-300µm in diameter. Asci are numerous, hyaline, clavate and measure 50-60 × 7-10.5µm., Each ascus contains eight ascospores arranged biserially. Intermixed with asci are present, numerous delicate paraphysis. New physiological races differing in their pathogenicity to, sugarcane cultivars have been frequently reported from different parts of the world., , 11.4.3-Disease cycle, Seed sets from diseased canes are the chief means of survival and annual occurrence, of the disease. Once, the pathogen establishes, secondary spread occurs by conidia. Ratoon, crops also serve as a source of perennation and inoculum multiplication. High humidity,, water-logging conditions, lack of proper cultural operations and continuous cultivation of, same variety year after year are the main factors responsible for the development of the, disease., , 11.4.4-Control measures, The following measures may be adopted for the control of red rot of sugarcane:, Healthy seed selection., Cultural practices-ratooning results in the multiplication of the disease, hence it must, be discouraged., Field sanitation and crop rotation., Use of resistant varieties like Co 846, 951, 975, 1007, 1148, 62101, 62399, S109,, BO22, 22, COLK 7702, 7710, etc., Treatment of seed setts with organo-mercurials like aretan or agallol (0.25%, suspension) helps in eradication of superficial inoculum. Besides, treatment of setts in, 0.5% bavistin solution reduces the incidence of red rot from infected setts., , 11.5 LOOSE SMUT OF WHEAT, Loose smut, a very serious disease of wheat, is world-wide in occurrence and is a, serious problem in the humid and semi-humid wheat growing regions. In India, the disease, occurs in all wheat growing areas, but its incidence is higher in the cooler and moist northern, parts than in the south. According to an estimate, the disease causes about 40% loss in wheat, yield every year., , 11.5.1 Symptoms, It is very difficult to detect infected plants in the field until heading. At this time, infected, heads emerge earlier than normal heads. The entire inflorescence is commonly affected and, appears as a mass of olive-black spores, initially covered by a thin gray membrane (Fig.4)., Once the membrane ruptures, the head appears powdery. Spores are dislodged, leaving only, the rachis intact. In some cases remnants of glumes and awns may be present on the exposed, rachis. Smutted headsare shorter than healthy heads due to a reduction in the length of the, rachis and peduncle. All or a portion of the heads on an infected plant may exhibit these, UTTARAKHAND OPEN UNIVERSITY, , Page 255
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , symptoms. While infected heads are shorter, the rest of the plant is slightly taller than healthy, plants. Prior to heading affected plants have dark green erect leaves. Chlorotic streaks may, also be visible on the leaves., , Fig.11.4. Loose smut of wheat: infected inflorescence, , 11.5.2-Morphology of the causal organism, The fungus responsible for the disease is Ustilago nudavar tritici. The mycelium of this, fungus consists of multicelluar hyphae which are hyaline but turn brown at maturity. The, primary mycelium is septate and uninucleate, whereas the secondary mycelium is branched,, septate and bi-nucleate. In vegetative phase the secondary mycelium is profusely branched, and spreads in intercellular spaces of the host tissues. The pathogen reproduces by the, formation of chlamydospores and basidiospores. The hyphal cells are transformed into, olivaceous brown, spherical and echinulate chlamydospores which germinate readily and, produce basidia and basidiospores. The haploid basidiospores produce uninucleate primary, mycelium on germination., , 11.5.3-Disease cycle, Ears of infected plants emerge early. The spores released from the infected heads land on the, later emerging florets and infect the developing seed. Infection during flowering is favored by, frequent rain showers, high humidity and temperature. The disease is internally seed borne,, where pathogen infects the embryo in the seed (Fig.11.5)., , UTTARAKHAND OPEN UNIVERSITY, , Page 256
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Fig.11.5: Ustilago nuda causing Loose smut of wheat disease showing disease cycle, , 11.5.4-Control measures, 1. Sow certified seed of wheat varieties that are resistant to loose smut and recommended for, your area by your nearest Extension adviser. None of the wheat varieties are resistant to all, the physiologic races of the loose smut fungus, however some are moderately to highly, resistant., 2. If you grow a variety susceptible to loose smut, be sure to plant certified seed purchased, from a reliable dealer. Certified seed carries a minimum amount of infection. Only wheat, fields that meet rigid specifications with respect to disease will pass certification, requirements. Competent inspectors closely examine fields of all growers who apply for seed, certification to make sure that no loose smut, or other serious seedborne wheat diseases are, present., 3. The best insurance against loose smut is seed treatment with a fungicide containing, carboxin or triadimenol systemic fungicides applied to the seed. These fungicides have the, unique ability of being taken up by the germinating seed. They check or kill the loose smut, fungus within the seed while controlling surface-borne bunt or covered smut and a number of, fungi that cause weedling blights (damping-off). Carboxin is sold under various trade names, UTTARAKHAND OPEN UNIVERSITY, , Page 257
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , often in combination with another fungicide. These mixtures give excellent smut control and, also provide protection against a wide range of fungi that attack the germinating seed and, young seedling., 4. The hot-water soak technique for ridding wheat seed of the loose smut fungus, while, highly effective, is difficult to use and often reduces the germination percentage and vigor of, the wheat seed. This procedure should be attempted only by experienced personnel with the, necessary equipment., , 11.6 SUMMARY, Fungi are a group of such plants which lack root system and chlorophyll. Hence, they lack the, capacity of mineral absorption and photosynthesis. They obtain their nutrition from other, living or dead plants and animals. Most fungi are saprophytic, i.e., they obtain their nutrition, from dead organic matter. There are certain fungi which obtain their nutrition from living, cells. These are known as parasitic fungi. These fiungi also affect the physiological processes, of the host. The toxins produced by certain fungi cause morphological deformity in the host., Such effects of the parasite appear in the host plant in the form of disease symptoms. The, disease caused by these fungi include late blight of potato, Red rot of sugarcane, Loose smut, of wheat etc., which can be controlled by number of methods, i.e. chemically or biologically., , 11.7 GLOSSARY, Acervulus: A mat of hyphae giving rise to short conidiophores closely packed together, forming a bed-like mass., Ascus: The cell in which nuclear fusion occurs in ascomycetes and in which ascospores, subsequently develop., Chlamydospore: A thick-walled, resistant spore formed by the direct differentiation of the, cells of the mycelium., Chlorosis: Yellowing due to lack of chlorophyll., Epiphytotic: A widespread occurrence of a plant disease., Fungus: The achlorophyllous thalloid microorganisms with filamentous and branched, somatic structure, cell wall demonstable nuclei and capable of reproducing typically by, sexual and asexual methods., Host: A living organism harboring a parasite., Parasite: An organism that derives its nourishment from a living organism (host)., Rot: Fungal infection resulting in softening, discolouration and disintegration (in some types), of succulent plant tissues., Smut: The diseases in which infected plants show masses of dark, powdery spores caused by, members of Ustilaginales., , 11.8 SELF ASSESSMENT QUESTION, 11.8.1-Fill in the blanks:, UTTARAKHAND OPEN UNIVERSITY, , Page 258
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 1. The disease of sugarcane is caused by……………………………….., 2. Causal organism of early blight of potato is ……………….., 3. CO846 and BO22 is the resistant varieties of……………….crop., 4. A widespread occurrence of a plant disease is called……………………, 5. Carboxin is a ……………..fungicide., 6. Glomerellatucumanensis is the perfect stage of the fungus………………, , 11.8.2- Choose the correct answer from the given below:, 1. An organism that derives its nourishment from a living organism is called, (a) Pathogen, (b) Saprophyte, (c) Parasite, (d) Host, 2. Late blight of potato is caused by, (a) Alternariasolani, (b) Albugo candida, (c) Phytophthorainfestans, (d) Colletotrichumfalcatum, , 11.8.3- True or False (T/F):, 1. Red Rot of sugarcane is caused by Colleotrichum falcatum., 2. Loose smut of wheat is caused by Xanthomonas oryzae., , Answers keys:, 11.8.1: 1. Colleotrichumfalcatum, 2. Alternariasolani, 3. Sugarcane, 4. Epiphytotic, 5., Systemic, 6. Colleotrichumfalcatum,, , 11.8.2: 1. (c), 2. (c),, 11.8.3: 1.True, 2. False, , 11.9-REFERENCES, , , , , Butler E. J.1906.Fungus disease of sugarcane in Bengal. Memoirs of the Department of, Agriculture Indian Botanical Survey 1, 2–24., Sharma, P.N. 2011. Principles of Plant Pathology, Department of Plant Pathology CSK, HPKV, Palampur., http://www.hortcouncil.ca, , 11.10-SUGGESTED READINGS, UTTARAKHAND OPEN UNIVERSITY, , Page 259
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , , , , , , , , , , , , , , , , BSCBO-101, , Bilgrami, K.S. 1985. Text Book of Modern Plant Pathology.Bishen Singh Mahendra Pal, Singh Dehradun., Butler, E.J. 1973. Fungi and Disease in Plants, Intern, Book Distributers.Dehradun., David S. Ingram , 1999. Plant Disease. Harper Collins Publishers, London United, Kingdom., Mehrotra, R.S. and Aneja, R.S. 1998. An Introduction to Mycology.New Age, IntermediatePress., Mishra, A.K. and Bohra, A. 2005. Plant Pathology: Disease and Management, Publ. Agrobios, Jodhpur, pp714., Sambamurty, A.V.S.S. 1992. A Text book of Plant Pathology.I.K. International Pvt. Ltd., 504p., Singh V, Pandey PC and Jain DK. 2005.A Text Book of Botany, Rastogi Publ. Meerut., Singh, R.S. Principle of Plants Pathology. Oxford and IBH Publ. Co. New Delhi, Singh, R.S.983. Plants Diseases.Oxford and IBH Publ. Co. New Delhi., Strobel, G.A. and D.E., Mathre 1970. Outlines of Plant Pathology. Van NostrandReinhold, Co. New York., Tarr, S.A.J. 1972. The Principle of Plants Pathology. Winchester Press, New York., Western, J.H. 1971. Diseases of Crop Plants.McMillan Press London., , 11.11-TERMINAL QUESTIONS, Q.1-Write causal organism, disease cycle and control measures of any two fungal diseases., Q.2-Write short notes on Red Rot of Sugarcane and Loose smut of wheat., Q.3- Differentiate Ascospores and Basidiospores., Q.4-Write short note:, a) Define Ascospores, b) What is a pathogen and parasite?, c) Define the term Epiphytotic., , UTTARAKHAND OPEN UNIVERSITY, , Page 260
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , UNIT-12- PLANT PROTECTION AND CONTROL, MEASURES PLANT DISEASES, 12.1- Objectives, 12.2- Introduction, 12.3- Plant protection, 12.4-Control measures of plant diseases, 12.4.1-Prophylactic measures, 12.4.2-Curative measures, 12.4.3-Biological measures, 12.5- Summary, 12.6- Glossary, 12.7- Self assessment questions, 12.8- References, 12.9- Suggested readings, 12.10- Terminal questions, , UTTARAKHAND OPEN UNIVERSITY, , Page 261
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 12.1- OBJECTIVES, After reading this unit student will be able:, , , , , , To understand the meaning of plant protection and its aims., To study the various procedures of plant protection and their impact on the, environment., To understand the disease cycle – disease control mechanism., To study the various control measures of plant diseases., , 12.2- INTRODUCTION, There are many infectitious organisms (pathogens) present in the environment that cause, different types of diseases in plants. Plant disease epidemics can cause famines, destroying a, thriving industry or can poison animals and humans. In order to control and eradicate the, pathogen, Plant protection plays a very important role in the management of plant diseases., Successful disease control requires thorough knowledge of the causal agent and the disease, cycle, host-pathogen interactions in relation to environmental factors, and cost. Disease, control starts with the best variety, seed, or planting stock available and continues throughout, the life of the plant., Agro-technical method was used for the first time for plant protection early in the 20th, century by the Russian entomologist N. V. Kurdiumov. The German scientists P. Zorauer and, G. Gassner; the American scientists G. Keitt and R. Sprague; and the Swiss scientist E., Gäumann worked further for the development of this technique, Correct crop rotations were considered a very important measure because the continuous, cultivation of any annual plant results in the concentration of pests and causative agents of, diseases. Their numbers can also frequently be reduced by appropriate methods of cultivating, the soil., , Protection, Preventing infection by creating a chemical toxic barrier between the plant surface and, pathogens., , , , , , Chemical treatment, Chemical control of insect vector, Modification of environment or environment condition, Modification of host nutrition, , 12.3-PLANT PROTECTION, Plant Protection focuses on keeping plants healthy---from diagnosing diseases to, implementing environmentally friendly pest-management practices. With an ever-expanding, UTTARAKHAND OPEN UNIVERSITY, , Page 262
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , population and increasing pressure on food and fiber supplies, Plant Protection plays a vital, role in improving our quality of life., Plant protection is a branch of agricultural science that devises ways and means of controlling, diseases, pests, and weeds of crops and trees, as well as a set of measures used in agriculture, and forestry to prevent and eliminate the damage done to plants by harmful organisms., The goal of plant protection is not only to destroy harmful organisms or limit their activity, but also to forecast the time they appear and the possible extent to which they might spread,, as well as to prevent especially harmful organisms from moving from one country and region, to other., Plant protection is based on the data obtained by several agronomic, zoological, and botanical, disciplines; genetics; biochemistry; plant and animal biochemistry and physiology. Plant, protection is closely related to such sciences as meteorology and climatology; chemistry and, physics, which provide the scientific basis of chemical and biophysical control methods; and, hygiene and toxicology, which study the direct and indirect effects of pesticides on plants and, animals., Ever since humans have relied on planted crops as the main source of food, plant diseases,, insects, rodents, weeds and other pest organisms have been a constant threat to food supply,, therefore plant protection plays a very important role in controlling loss and damage to the, important food crops and plants., , Process of plant protection, A fundamentally important starting point for plant protection is the ability to anticipate the, emergence and spread of noxious organisms and to prevent their introduction and spread, before they become agricultural pests in specific crops and regions., The various steps in plant protection are quite similar to those of human medicine., 1. To diagnose the problem which involves proper identification of the organisms responsible, for the damage symptoms observed., 2. To assess the extent of the damage and the yield or revenue loss likely to result from this, damage, which helps grower to make decisions on whether to invest resources in combating, the pest., 3. To consider the various options available for controlling pests, including host plant, resistance, cropping system and cultivation practices that reduce pest populations., , Plant protection measures, Plant protection measures are carried out to limit performance and yield losses in crop, production during the growing season and afterwards (storage protection) as well as for, quarantine purposes. They serve primarily to safeguard yields, although in combination with, other cultivation measures they can also help to raise yields., A wide variety of individual measures - with varying ecological, economic and socioeconomic impacts - are available for keeping harmful organisms (diseases, pests, weeds), below the economic threshold. To reduce the probability of damage, preventive measures are, taken in the areas listed below:, - site design (hedges, border strips, tree guards etc.), UTTARAKHAND OPEN UNIVERSITY, , Page 263
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , - site and variety selection, - sowing, planting, - healthy seed and planting stock, - crop rotation, intercropping, - tillage, land improvement, - crop tending, - harvesting, - storage, Measures in these areas are backed up by the following direct forms of plant protection:, - physical methods, - chemical methods, - biotechnical methods, - biological methods, - integrated methods, , Physical methods, Physical methods directly destroy harmful organisms, aim to retard their development or, prevent them from spreading. They can be divided into mechanical and thermal measures., The mechanical measures include:, - Tillage to control weeds and pests (hoeing, removal of affected parts of plants and, intermediate hosts),, - Flooding of fields to combat soil-borne harmful organisms (e.g. Fusariumoxysporum,, which causes banana wilt),, - Laying of sticky belts to trap flightless insect pests and other measures for catching, pests or keeping them away from crops, such as fences, trenches (locust control), traps, and picking-off of pests., Thermal methods utilise the harmful organisms' sensitivity to high or low temperatures and, includes:, - Hot-water treatment of seed and planting stock (e.g. to combat viruses and bacteria in, sugar cane cuttings), - Solarisation (covering the surface of the ground with plastic sheeting produces, phytosanitary effects by virtue of the greenhouse effect resulting from insolation, e.g., for controlling parasitic seed plants, soil-borne harmful organisms etc.),, - Burning-over to control weeds and burning of crop residues. Low temperatures inhibit, the spread of certain storage pests., Chemical methods, Eradicative, protective and curative methods are used in chemical plant protection to destroy, harmful organisms or keep them away from plants, to protect plants against attack and, penetration by harmful organisms and to cure plants (or parts of plants) that have already, become infested or diseased., Chemical methods can be used in three ways:, 1. Soil treatments, UTTARAKHAND OPEN UNIVERSITY, , Page 264
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , 2. Seed treatments, 3. Foliar sprays, Soil treatments are designed to kill soil-inhabiting nematodes, fungi and bacteria. This can be, achieved by using steam or chemical fumigants. Soil borne nematodes can be killed by, applying granular or liquid nematicides. Most soil is treated well before planting; however,, certain fungicides can be mixed with the soil at planting time., , Fig.12. 1. Application of protective sprays, , Fig.12.2. Benefits of seed protectant, , Seed treatments consist of dusts o slurries applied to seed to protect it primarily against decay, and damping-off caused by soil borne pathogenic fungi. Seeds, bulbs, corms and tubers are, frequently treated with chemicals to eradicate pathogenic bacteria, fungi and nematodes., Protective sprays and dusts applied to the foliage and fruit crops and ornamentals include a, wide range of organic chemicals designed to prevent infection. Protectants are not absorbed, by or translocated through the plant, thus they protect only those parts of the plant treated, before invasion by the pathogen (Fig.12.1, 12.2)., , Fig.12.3. A farmer applying pesticides to the crops, , Biotechnical methods, Biotechnical methods utilise the natural reactions of the harmful organisms to physical and, UTTARAKHAND OPEN UNIVERSITY, , Page 265
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , chemical stimuli in order to bring about changes in their behaviour for the purpose of plant, protection (e.g. light and colour traps, chemical attractants, antibodies, pheromones,, hormones, growth regulators). The emphasis is on measures which aim not to directly kill the, harmful organisms, but rather to permit population monitoring for the purpose of forecasting,, defensive action and deterrence. The harmful organisms can be killed by combining, biotechnical methods with chemical measures. Disease resistant varieties could be developed, through biotechnological methods., , Biological methods, Biological plant protection involves using organisms and their activity to protect plants and, enhance their resistance to biotic (harmful organisms) and abiotic limiting factors. For the, purpose of pest and disease control, beneficial organisms are specifically preserved and, fostered, released in large numbers or introduced into habitats where they have not been, found hitherto. Biological control of weeds has to date primarily involved introducing, beneficial organisms into new habitats., Another biological method is that of inducing resistance to disease. This can be done, for, example, by infecting plants with pathogens having low virulence., Biological insecticides, derived from naturally occurring microorganisms (e.g.: bacillus, thuringiensis, entomopathogenic fungi and entomopathogenic nematodes), also fit in this, category., Biological control also involves introduction of exotic species, or it can be a matter of, harnessing whatever form of biological control exists naturally in the ecosystem in question., The induction of plant resistance using non-pathogenic or incompatible micro-organisms is, also a form of biological control. Some diseases that can be successfully controlled using, biological agents are pathogens of pruning wounds and other cut surfaces, crown gall,, diseases of leaves and flowers, such as powdery mildew, diseases of fruits and vegetables,, such as Botrytis, and fungal pathogens in the soil (disease suppressive soils)., , Integrated methods, Integrated plant protection is a concept which involves coordinated use of all ecologically, and economically justifiable methods in order to keep harmful organisms below the economic, threshold. The emphasis is on utilising natural limiting factors. The main aim is to preserve, the balance of nature as far as possible; this is to be achieved by reducing use of chemical, plant protection methods and simultaneously employing a variety of measures from the other, categories. It is here that the links with the plant production sector are particularly close., Use of pesticides is to be reduced to the essential minimum by abandoning the practice of, routine or calendar-based spraying, gearing pesticide dosage to actual conditions, refraining, from the use of broad-spectrum persistent agents (liable to harm beneficial organisms) and, selecting the time of application such that beneficial organisms suffer no adverse effects., Integrated plant protection methods generally prove more successful in permanent crops than, in short-lived crops. The limits and risks attaching to these methods become clear if the work, is performed by untrained personnel. Use of integrated plant protection methods generally, calls for detailed knowledge of biological, ecological and economic factors., UTTARAKHAND OPEN UNIVERSITY, , Page 266
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Environmental impact of plant protection, The environmental impacts of plant protection are caused by the influence of substances, and/or forms of energy on organisms and their functioning as well as on soil, water and air., The extent to which a plant protection measure is harmful, and in particular the degree to, which it is liable to cause lasting harm, is determined by its varied influences on the, functioning of the ecosystem., Harmful effects of environmental impacts are observed if plant protection measures fail to, take adequate account of ecological considerations. Repeated, one-sided application of a, particular active ingredient (like pesticides) will cause the harmful organism to develop, resistance to it., Although non-specific control methods control the spread of a harmful organism, they also, unintentionally affect numerous useful organisms. They, thus adversely influence the, diversity of species and biological regulation mechanisms, creating a risk that harmful, organisms may multiply more rapidly and it consequently needs additional plant protection, measures., It also has bad effects on the abiotic environment (e.g. soil erosion caused by tillage carried, out for the purpose of plant protection)., Plant protection is linked to other plant production measures and is thus subordinate to the, goals of plant production (cf. environmental brief Plant Production). Measures in the field of, plant production also have a bearing on the goals and environmental impacts of the following, sectors:, - Livestock farming (fodder, quality control), - Fisheries (prevention of water pollution), - Agro-industry (quality standards), - Health and nutrition, including drinking-water supplies (toxicology, residues), - Analysis, diagnosis, testing (quality control, development, analytical techniques), - Chemical industry (pesticide production), Decisions on plant protection measures may therefore be influenced by measures in these, areas. When assessments are being made, attention must be paid to the possibility that, impacts generated by the various sectors could have a cumulative effect and thereby increase, the amount of damage done., , 12.4-CONTROL MEASURES OF PLANT DISEASES, In controlling diseases, plants are generally treated as populations rather than individuals,, although some plants, especially trees, ornamentals and sometimes virus-infected plants are, treated individually., In control of diseases of plants, the measures are mostly preventive i.e. Prophylactic, and, there are only a few situations where diseased plants are cured individually by treatment i.e., therapeutic, or curative. Thus, except cases as diseased tree, fruit or some ornamentals, where, curative methods are used, in general, care of healthy plants is taken in advance to prevent, their infection., UTTARAKHAND OPEN UNIVERSITY, , Page 267
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Factors in the control of plant diseases:, 1. Soil management., 2. Selection of disease-resistant plants (cultivars)., 3. Proper watering of plants., 4. Protection of plants from extreme weather conditions., 5. Rotation of crops., The soil selected for cultivation should be good. The best soil for most plants is loamy, with, good drainage and aeration. This minimizes diseases that attack the roots and allows the roots, to feed nutrients from the soil to the rest of the plant. Organic methods, such as the addition, of compost, can improve soil quality, and fertilizers can be added to the soil to enrich the, nutrient base., Disposal of infected plants is important in the control of diseases, as is the careful, maintenance of tools and equipment used in farming and gardening., Crop rotation is an important part of reducing plant diseases. Pathogens that favor a specific, crop are deprived of their preferred host when crops are rotated. This reduces the virulence of, the pathogen and is a natural way to reduce plant disease., , Methods of control, The main methods of plant disease control have been categorized in different ways. Basically, there are three main control measures:, Prophylactic measures, Curative measures, Biological measures, , 12.4.1- Prophylactic measures, Prophylaxis aims protection of host plant from infection in following three major ways:, 1. Avoidance of the pathogen: Occurrence of a disease can be avoided by planting/sowing, a crop at times when, or in areas where, inoculum remain ineffective/inactive due to, environmental conditions, or is rare or absent. Avoidance can be carried out by:, (i) Choice of geographical area, (ii) Selection of a field, (iii) Adjustment of time of sowing, (iv) Use of disease escaping varieties, (v) Use of pathogen-free seed and planting material, , (i) Choice of geographical area: Selection of geographical area for any crop is made on, the basis of suitability of climate for the crop. The same climate may be suitable for the, activities of the pathogen also. Many fungi and bacterial disease are more severe in wet areas, than in dry areas., Crops susceptible to such diseases can be grown in dry areas with the help of irrigation. Bean, anthracnose disease is common in wet areas where seeds produced are generally infected. For, seed production of bean dry areas are always preferred. Smut and ergot of pearl millet are, UTTARAKHAND OPEN UNIVERSITY, , Page 268
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , serious in areas where rains occur for long duration; therefore cultivation of this crop in such, areas is not profitable., (ii) Selection of a field: For successful cultivation of a crop, a proper field is necessary. If a, disease caused by a soil-borne pathogen has been located in a field, it is not used to the same, crop for some time. In such diseases, as bacterial wilt of potato, wilt of pigeonpea, smut of, pearl, millet, root knot of nematodes the infested field can be avoided.In selecting a field, drainage, management is also important. Poor drainage can lead to disease., (iii) Adjustment of time of sowing: In many diseases the incidence or disease severity is, most serious when susceptible stage of the plant growth coincides with favourble conditions, for the pathogen. This coincidence can be avoided by alteration in date of planting. It helps in, avoiding critical period. Thus, late sown winter crops escape incidence of root rot and wilt, favoured by high temperature and moisture that usually occur after the summer rainy season., (iv) Use of disease escaping varieties: In different crops, certain varieties escape damage, by disease because of their growth characters, not due to their genetic resistance to the, disease. In India, varieties of peas that mature early generally escape much damage from, powdery mildew which becomes serious in January or later., (v) Use of pathogen-free seed and planting material: Diseases which are carried by, seed or vegetative planting material and spread the infection in the field require proper, selection of seed to avoid multiplication of the pathogen in the field. This can avoid, contamination of healthy crop. Therefore planting of disease free seeds in pathogen free soil, is often the most effective measure of control of certain diseases., , 2. Exclusion of the pathogen: This can be achieved by preventing the inoculum from, entering or establishing in a field or area when it does not exist. Legislative measures like, quarantine regulations are needed to be strictly applied to prevent spread of a disease., Exclusion can be carried out by:, (i) Treatment of seed and planting materials, (ii) Inspection and certification, (iii) Quarantine regulations, (iv) Eradication of insect vector, , (i) Treatment of seed and planting materials: Seed tubers, grafts, bulbs and other, propagation materials can be given heat, gas or chemical treatments to exclude the pathogen, present in or on them. Seed treatment methods are mandatory for seed agencies supplying, certified seeds. Generally seed treatments are prescribed for imports also and the exporting, agency has to provide a certificate regarding this for quarantine purposes., (ii) Inspection and certification: The crops grown exclusively for seed are periodically, inspected for presence of diseases that are disseminated by seed. Necessary precautions are, taken to remove the diseased plants. The produce is certified as seed. The badly affected plots, and seed lots are usually rejected. The method is supposed to prevent regional and interregional spread of seed-borne pathogens., , UTTARAKHAND OPEN UNIVERSITY, , Page 269
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (iii) Quarantine regulation: Plant quarantine aims at preventing entry of pathogens from, infested areas into no-infested areas at international or national level. If in a particular area,, some disease is present in serious form and is likely to be disseminated by propagating, materials, the government passes necessary regulations. For implementation of these, regulations at the international level, proper check is maintained at the points of entry, (airports and seaports). Suspected material is kept under quarantine for a specific period and, if found contaminated it is either destroyed or effectively treated., (iv) Eradication of insect vector: For effective exclusion of pathogens that can gain entry, into a new area through insect vectors or carriers particularly insects having long flight range,, a check on these vectors is necessary. Since the flight of insects cannot be checked, the crop, should be given insecticidal cover before arrival of the vectors on the plant surface., , 3. Eradication of the pathogen: It includes reducing, inactivating, eliminating or, destroying inoculum at the source, either form a region or from an individual plant (rouging), in which it is already established. Eradication can be achieved by:, i. Biological control of plant pathogens, ii. Crop rotation, iii. Removal and destruction of diseased plants or plant parts, iv. Eradication of alternate and collateral hosts, v. Heat and chemical treatment of diseased plants, vi. Soil treatment: by use of chemicals, heat energy, flooding and fallowing, (i) Biological control of pathogens: This type of control aims at eradication and reduction, of inoculums and protection of plant surfaces through the activity of other microorganisms. It, includes activities that enhance microbial numbers and quality on plant surfaces in soil or on, the leaf., (ii) Crop rotations: When the same crop is raised year after year on the same land the soilborne pathogens of that crop easily perennate in the soil becomes so heavily infected that it, becomes unfit for cultivation of that crop. On the other hand, when immune, resistant or nonhost crops are grown for a definite duration after a susceptile crop in the field it is expected, that the pathogen will be weakened, starved and killed. It is also possible that different crops, modify the chemical and biotic environment of the soil against the pathogens. Crop rotation, is the oldest methods of fighting soil against the pathogens., (iii) Removal and destruction of diseased plants or plant organs: the presence of, diseased plants in the field is a source of continuous release of inoculums. Therefore, as far as, possible, such plants or their affected organs should be removed and destroyed to reduce the, amount of inoculum., (iv)Eradication of alternate and collateral hosts: The removal of alternate or collateral, hosts is also recommended. Plant organs bearing dispersible pathogens propagules and their, vectors should be removed carefully so that they are not dispensed while the plant or its, organs is being physically removed., , UTTARAKHAND OPEN UNIVERSITY, , Page 270
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (a) Roguing: This practice involves removal of diseased plants or their affected organs from, the field. This method can be applied to diseases caused by fungi, bacteria, viruses as well as, nematodes., (b) Sanitation: Field sanitation is essential for control of soil-borne and facultative parasites, or saprophytes. Many obligate parasites also perennate through dormant structures in plant, organs lying in or on the soil. Destruction of crop debris by burning in the field decreases this, type of survival of pathogen in the field. Sanitation is very important when diseased crop, residue is left on the field as a general practice by the farmers., (v) Heat and chemical treatment of the diseased plants:The pathogen present in the, plant or in its special organs can be inactivated or killed by heat or chemical treatments. This, approach has been found useful mostly in virus diseases of fruit trees. Heat therapy, inactivates viruses in fruit tree seedlings and grafts and destroys the exposed fungal and, bacterial propagules. Bare root dip in nematicides or fungicides is a method of sanitizing the, seedlings before transplanting., (vi) Soil Treatments: The aim of soil treatment is to inactivate or eradicate the pathogens, present in the soil. It involves the use of chemicals, heat and such cultural practices as, flooding. In chemical treatment of soil, fungicides and fumigant or granular nematicides are, generally used. Most of the fungicides are selective in action and destroy specific fungi., Therefore, by their use the development of other non-target pathogens may increase due to, reduced microbial competition., Soil solarization is a novel method of soil treatment to destroy most fungal, bacterial and, nematode propagules as well as weed seeds., Flooding of the field is a method of eradicating fungal and nematodal pathogens from the, field. If about 30 cm deep water is allowed to stand in the field for several weeks, the, anaerobic or low oxygen conditions and toxins produced by the anaerobic bacteria destroy, fungal scleratia and plant parasitic nematodes., , Fig.12.4. Different chemicals used in chemical control of diseases, , 4. Protection of the host: Host plants can be protected by creating a toxin barrier on the, host surface by the application of chemicals. Various methods can be used in order to achieve, protection:, i. Chemical control: application of chemicals (fungicides, antibiotics) by seed treatment,, dusting and spraying, ii. Chemical control of insect vectors, iii. Modifications of environment, UTTARAKHAND OPEN UNIVERSITY, , Page 271
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , iv. Modification of host nutrition, , (i) Chemical control: The aim of most chemical sprays, dusts and seed treatment is to form, a protective toxiclayer on the host surface so that when the pathogen comes in contact with, the surface it is killed or prevented from growth. The chemicals used for this type of, protection are called protective chemicals. The same chemical can be protectant as well as, eradicant. The use of systemic fungicides or naematicide is protectant as well as eradicant. It, destroys the pathogen present within the plants (Fig.12. 4)., , I. Direct protection by chemical controls, Chemical compounds which are toxic to the pathogens can be used for controlling disease in, the fields and in greenhouses., Such chemicals either inhibit germination, growth and multiplication of the pathogen or are, lethal to the pathogen. Sulphur, copper, zinc and mercury compounds have been used for last, more than 150 years., Chemicals used in plant protection are termed as pesticides, and depending on the kind of, pathogens they affect, the chemicals are called fungicides, bactericides, viricides,, nematicides, insecticides, herbicides and so on., Most of the chemicals are used to control diseases of the foliage and other aboveground parts, of plants., Some are used to disinfect and protect seeds, tubers and bulbs from infection. Some are used, to disinfest the soil, others to protect stored fruits, vegetables from infection., Different groups of chemicals are in use as fungicides, different terminologies are used for, fungicides, they are as follows:, (a) Protectants: These kill the pathogen before it attacks the plants. They are thus designed, to be present at the infection court in advance of the pathogen in order to prevent infection., While acting in this way, they may also have a direct effect on organisms which have already, invaded the host. In this case they act as eradicants. As a rule protectants are of relatively, little value as eradicants., (b) Therapeutic (Direct or eradicants): These fungicides are applied after attack and kill, fungi after they have invaded the plant. They may be fungistatic preventing the growth or, spore suppressants preventing sporulation. They are further categorized as : contact, fungicides and residual fungicides., , UTTARAKHAND OPEN UNIVERSITY, , Page 272
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , The former is applied before or after it has found the host plant, while the later is applied, before the fungus reaches to it so that chemicals forms a protective layer over the plant, surface., II Chemical methods to eradicate or reduce the inoculums, A few chemicals are curative in nature and used to eradicate a pathogen that has already, infected the plant. In addition to these, there are a few chemical treatments that act as, eradicating or greatly reducing the inoculums before it comes in contact with the plant. These, are as follows:, (a) Soil treatment : soil to be planted with vegetables, fruits, ornamentals or high value, crops like tobacco is frequently treated with chemicals for control mainly of nematodes, but, occasionally also of soilborne fungi, such as Fusarium, Verticillium, weeds and bacteria., Fungicides used for soil treatment include: metalaxyl, diazoben, PCNB, captan, chloroneb., Nematodes are controlled by soil fumigation with one of the nematicides applied before, planting. Commonly used nematicides are: chlorpicrin, methyl bromide, dazomet and metam, sodium., (b) Disinfestation of warehouses: in order to remove any pathogens left over from, previous years, the storage rooms are first cleaned thoroughly, debris are removed and burnt., The walls and floors are washed with bleach (a CuSO4 sloution 1 lb in 5 gall. Of water). In, the room, the relative humidity maintained at 100% and temperature between 25 and 30oC,, and fumigated with chloropicrin (tear gas)., (c) Insecticides: for controlling insect vectors of fungal and bacterial pathogens, insecticides, are to be used. Virus transmission by insects can also be reduced by spraying the plants, several times with mineral oil. This method has been found effective in control of cucumber, mosaic virus on cucumber., , (ii) Chemical control of insect vectors: many diseases are due to insect vectors. Some, viruses are transmitted only by insect vectors. If a plant which has been sprayed by an, insecticide, many of them escaped instant death and may infect healthy plant. The success of, chemical control of insect vectors depends to a great extent on the stage of plant growth and, nature of the pathogen. It also depends on the speed with which the chemical can kill the, insect. Those chemicals which kill the insects within few seconds are most effective in, control of insect-transmitted diseases., , (iii)Modification of environment: Improvement of aeration under crop canopy reduces, humidity on leaves and other aerial parts and thereby checks growth of fungi which flourish, in humid atmosphere. Reducing the number of irrigations also helps in modification of, environment against certain diseases. Mixed cultivation of crops, one of which provides, ground cover, often provides low temperature and high soil moisture. These conditions are, not favourable for some root pathogens. Root diseases favoured by high temperature are often, controlled by irrigation. Aeration through proper ventilation of the store house provides, proper environment for storage of plant products. Cold storage can provide protection to, fruits and vegetables by post-harvest decay., UTTARAKHAND OPEN UNIVERSITY, , Page 273
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , (iv) Modification of host nutrition: The disease of a plant is often influenced by host, nutrition. It generally acts through strengthening of the tissues. Many leaf diseases are, fovoured by high level of nitrogen in the soil. Lowering nitrogen in soil in such disease is a, method of checking such disease. In rice application of 100 kg N/ha instead of 120 kg is, recommended to prevent from leaf spots, blast and sheath blight. Deficiency of potash in, plants renders the tissue susceptible to water soaking and many more diseases. High calcium, increases resistance to wilt and soft rot diseases. Intensity of several diseases is decreased by, such micronutrients as zinc, boron and manganese etc., Antibiotics: are metabolites of microorganisms which in very dilute concentration, and have, the capacity to inhibit growth of or destroy other microorganisms. Antibiotics have systemic, action in plants moving in both directions, from leaves to roots and from roots to the foliage., They are not only eradicants but also protectants providing temporary resistance in the host., The antibiotics used in plant disease control mainly belong to groups known as streptomycin,, tetracyclines, polyenescyclo hexilmide and griseofulvin., Streptomycin was the first antibiotic used in plant disease control, it was used against fire, blight of pear (Erwinia amylovora) in 1953., Antibiotics in the tetracycline group are tetracycline (Acromycin), oxytetra cycline, (Teramycin) and chloretetracycline (Aureoycin). These antibiotics are bacteriastatic and, bactericidal., Aureogungin, a heptoene antifungal antibiotic, is recommended for the control of rice leaf, spot, rice blast, barley stripe disease and covered smut of barley through seed treatment., Nematicide: Nematicide belongs to two groups: volatile soil fumigants and non-fumigants, (contact and systemic fungicide). The fumigants consist of compounds belonging to, halogenated hydrocarbons and isothiocyanate groups while the non-fumigants are mostly, organo-phosphorus and carbamates. The former directly kill the nematode larvae while the, latter do not cause direct kill. Eggs are generally not affected by nematicieds being protected, in cysts or in crop debris., The soil fumigants such as methyl bromide, ethylene dibromide, D-D mixture, methyl, isothiocyanateetc pose high vapor pressure, get dissolved in soil moisture in concentrations, high enough to kill nematode larvae and disperse through the soil pores., The halogenated hydrocarbon group includes methyl bromide, ethylene dibromide, Toluene,, Nemagon and chlorpicrin., The isothiocyanate group includes fumigants that release methyl cyanate such as Vapam,, Dazomet, Mylone or Basamid., The non-fumigant nematicides have gradually replaced the fumigants. They are available in, granular form and can be applied to rows of crops at the time of planting or to soil around the, standing trees., The contact non-fumigants include fenulphathion (Dasanit or Terracur P), thionazin, (Nemafas, zinophos), diazinon (Basudin) and ethoprop., Non- conventional chemicals in disease control: minerals and vegetable oils have been, used as plant control measures. Large scale use of mineral oil for control of Shigatoka disease, of banana was prevalent in the past., , UTTARAKHAND OPEN UNIVERSITY, , Page 274
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Oil of sunflower, olive, maize and rapseed have antifungal properties and have shown, efficacy against powdery mildew of apple., Significant control of grapevine powdery mildew with rape oil derivative is reported from, Australia. Groundnut oil coating prevents papaya fruit decay. Similarly, aqueous extracts of, many plants are also reported to provide control of fungi, bacteria and viruses., Some herbicides are known to directly affect a disease. The herbicide propanil has antifungal, activity against Drechsleraoryzoe., , 5. Disease resistance: It is a method of preventing infection or reducing the effect of, infection of the pathogen through the use of resistance host which is developed by genetic, manipulation or by chemotherapy., , Use of resistant varieties: Development of resistance in host is done by, i. Selection and hybridization for disease resistance, ii. Chemotherapy, iii. Host nutrition, iv. Genetic engineering, tissue culture, , (i) Selection and hybridization for disease resistance: Selection of resistant individual, with poor commercial qualities and hybridizing them with susceptible plants of high, commercial qualities is the aim of developing resistance through hybridization. This, technique can help to produce disease resistant varieties and use of such varieties not only, eliminates loss due to disease but also saves money to be spent on chemicals and other, methods of control., , (ii) Chemotherapy: Temporary physiological resistance in plants can be developed through, chemotherapy. Systemic fungicides and antibiotics when applied to the foliage or through the, roots persist in the plant for some time and while their toxic level is maintained the pathogen, cannot invade the tissue. Systemic nematicieds applied to soil and taken up by the plant keep, away not only the nematodes but also aphids and leafhoppers for several weeks. This protects, the plant against viruses too., , (iii) Host nutrition: Nutrition cannot change a susceptible variety to a resistant variety. But, making available major and micronutrients through foliar sprays, seed treatment or soil, application is reported to strengthen the tissues that can ward off invasion by the pathogen., Although the effectiveness of this approach is doubtful, a vigorous growth of the plant is, always desirable. Vigorous plants with capacity to form new roots and shoots to replace the, damaged once tolerate the attack of many diseases. Application of Nitrogen more than, required for normal development of the plant causes new succulent growth of vegetative parts, and also delays maturity., , (iv) Genetic manipulation through biotechnology:Plant tissue culture and genetic, engineering are being used for genetic manipulation a multiplication of plants. This has, UTTARAKHAND OPEN UNIVERSITY, , Page 275
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , enabledhybridization between species which normally do not hybridize or those plants which, normally do not produce viable seeds. Creation of transgenic plants in which resistance genes, from sources other than the particular plant species or in which avirulence genes of the, pathogen are introduced to impart resistance is now possible., , Immunization or improvement of host resistance, Though there is no antibody producing system in plants, treatment with some pathogens, sometimes leads to temporary or permanent resistance. Besides this the genetic resistance of, the host can also be improved. Following are some examples of immunization and, improvement of host resistance methods:, i. Cross protection. This is protection of plants by mild strain of a virus from infection by a, virulent strain of the same virus. This is general phenomenon among viral pathogen., ii. Induced resistance. In some cases, a plant infected by one pathogen becomes resistant, to subsequent infection by another pathogen. Bean and sugarbeet inoculated with virus show, greater resistance to some obligate fungal pathogens (rusts, powdery mildew). TMV in, tobacco induces resistance to Phytophthoraparasiticavar.nicotianaeand to bacteria, Pseudomonas tabaci., iii. Improving the growth conditions of plants. This is done by using some cultural, practices that improve the plant vigour and help increase its resistance. Proper fertilization,, field drainage, irrigation, proper spacing between plants and weed control are useful in this, direction., iv. Use of resistant varieties. This is the safest and most effective method of disease, control. Once successful, it eliminates expenses of chemicals or time spent in other methods., Farmers could get maximum gain through the use of resistant varieties of field crops,, particularly cereals. Several techniques are used for enhancing the useful life span of a, resistant variety., , 12.4.2- Curative measures, These are the measures applied after the plant is infected (i.e. the plant is treated for the, disease). This can be illustrated by heat or chemical treatment of vegetative parts such as, bulbs, corms and woody cuttings to eliminate pathogens that are established within the plant, material. Although cure of the diseased plant or its organ in most crops is not possible or, extremely difficult in many crops and fruit trees chemical and physical therapy has been, applied to cure the plant by eradicating the pathogen., Curative or therapeutic measures include:, i. Heat or thermotherapy, ii. Chemotherapy, iii. Tree surgery, , (i) Heat or Thermotherapy: Plants which can tolerate the thermal inactivation or death, point of the pathogen can be treated by heat to destroy the pathogen. These treatments are, especially used for seed, tubers, bulbs and grafts. Grafts of fruit trees are exposed to high, temperatures for inactivation of many viruses. For inactivation of nematodes from roots of, UTTARAKHAND OPEN UNIVERSITY, , Page 276
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , grafts heat therapy has been suggested. Ratoon stunting bacterium and many viruses of, sugarcane are eradicated by hot water, air or moist hot air treatment of the seed conses., (ii) Chemotherapy: Chemical treatments applied to eradicate the pathogen from the tissues, of the diseased plant and thus curing it is called are included in chemotherapy. Such, chemicals are called chemotherapeutants. They are mainly systemic fungicides and, antibiotics. The principle underlying chemotherapy is site where the pathogen is present. It, either kills the pathogen or incapacitate it by preventing sporulation, growth or both. So long, as they remain at a toxic level they provide temporary resistance also. The, chemotherapeutants can also act by detoxifying the toxins produced by the pathogen. In this, way, the tissues not invaded by the pathogen are saved and the plant is cured., (iii) Tree surgery: In this technique the large size fruit trees are cleaned of infection by, cutting or scrapping of the diseased part and covering the wound with a fungicidal paste. This, removes the infection and saves the tree.it is concerned with the health of the trees and, treatment of diseases with various techniques including crown reduction, crown trimming,, pruning or tree felling., Trees in urban or populated areas require a higher level of care to maintain their safety and, aesthetics. Pruning should be done with an understanding of how the tree responds to each, cut, this can only be performed by a qualified arborist. Improper pruning can cause damage., This damage lasts for the life of the tree, and it shortens the life of the tree., , 12.4.3- Biological measures, Biological control of disease employs natural enemies of pests or pathogens to eradicate or, control their population. This can involve the introduction of exotic species, or it can be a, matter of harnessing whatever form of biological control exists naturally in the ecosystem in, question. The induction of plant resistance using non-pathogenic or incompatible microorganisms is also a form of biological control. Some diseases that can be successfully, controlled using biological agents are pathogens of pruning wounds and other cut surfaces,, crown gall, diseases of leaves and flowers, such as powdery mildew, diseases of fruits and, vegetables, e.g. Botrytis, and fungal pathogens in the soil (disease suppressive soils)., The most common mechanisms for microbial antagonism of plant pathogens are parasitism,, predation, competition, induced resistance and the production of antimicrobial substances., Often, several mechanisms act together., Biological control involves following methods:, 1. Eradication or reduction of the pathogen inoculums by antagonists, 2. Direct protection of plants by antagonists, 3. Improvement of plant resistance (Immunisation), , 1. Eradication or reduction of the pathogen inoculums by antagonists: Under some, situations biological methods can be used to eradicate or reduce the pathogen inoculums., These are as follows:, i. Suppressive soils. Several soil-borne pathogens, such as Fusarium oxysporum,, Phytophthora cinnammomi, Pythium sp. thrive and cause severe diseases in some soils called, UTTARAKHAND OPEN UNIVERSITY, , Page 277
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , conducive soils, whereas they develop much less and cause much milder diseases in other, soils, known as suppressive soils. This is due to the presence of several microorganisms,, antagonistic to the pathogens in these soils. These antagonists do not allow the pathogen to, reach high population by producing antibiotics, lytic enzymes and competition for food., Suppressive soil added to conducive soil can reduce the extent of disease by introducing, microbes antagonistic to the pathogen., ii. Biocontrol through hyperparasites. Hyperparasites prove ideal organisms for several, soilborne as well as aerial plant pathogens. Soilborne pathogens can be eliminated / reduced, by using appropriate hyperparasites, both fungi and bacteria. These fungi and bacteria infect, the resting spores of several pathogenic fungi. Among the most common mycoparasitic fungi, are Trichoderma spp. Which parasites mycelia of Rhizoctonia and Sclerotium, inhibits the, growth of many other fungi like Pythium, Phytpthora, Fusarium and reduce the disease, caused by most of these pathogens., Besides fungi, bacteria of the genera Bacillus, Enterobacter and Pseudomonas are known as, parasitic and inhibit the pathogenic fungi., iii. Trap plants. The pest is attracted from the main crop to a preferred plant the trap plant,, which is planted deliberately. Rows of rye, corn or other taller plants planted around a field of, bean, pepper or squash stop many incoming aphids carrying viruses that attack the bean,, pepper and squash. Since most aphid-borne viruses are non-persistent in the aphid, many of, the aphids loose bean, pepper or squash by the time they move into these crops. In this way, trap crops reduce the amount of inoculums reaching a crop. Trap plants are also used against, nematodes. Some plants, not susceptible to sedentary plant-parasitic nematodes produce, exudates that stimulate their eggs to hatch. The juveniles though enter these plants but unable, to develop into adults, and thus eventually die. Such plants are also called trap crops., iv. Antagonistic plants. Plants like asparagus and marigold are antagonistic to nematodes, because they release substance in the soil that are toxic to several plant parasitic nematodes., Like trap plants, however, antagonistic plants are also not being used so far on commercial, scale. Planting of marigold or tobacco around tomato has been found promising., , 2. Direct protection of plants by antagonists: As with chemicals, strategies have also, been evolved during recent past for direct protection of plants through the use of biological,, mainly microbial antagonists (fungal as well as bacterial). Biological control practices for, direct protection involve the deployment of antagonistic microorganisms at the infection, court before or after infection. Fungal as well as bacterial antagonists have been used., i. Fungal antagonists. Several fungi have been used in the biocontrol of both, soilborne as, well as airborne disease of plants, and also of postharvest diseases. For control of postharvest diseases of several fruits, spores of saprophytic yeasts and filamentous fungi are, sprayed at different stages of fruit development. Yeasts reduced postharvest rotting of peach, and apple., ii. Bacterial antagonists. Like fungi, several bacteria also have been successfully used for, the biocontrol of soilborne and postharvest diseases of plants. Crown gall of stone fruits,, pome and grapes caused by bacterium Agrobacterialtumefaciens is being controlled, commercially by treating the seeds, seedlings and cuttings with Galltrol, a suspension of, UTTARAKHAND OPEN UNIVERSITY, , Page 278
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , strain K84 of the related but nonpathogenic bacterium Agrobacterium rudiobacter. This, antagonist produces an antibiotic, bacteriocin, called agrocin 84 which inhibits agrobacteria, that arrives at the surfaces occupied by strain K84., iii. Viral parasites of plant pathogens. Viruses are known to attack all plant pathogensfungi bacteria, mollicutes and nematodes. Bacteriophages when mixed with bacterial, pathogens, successful control could be achieved in case of several bacterial diseases of plants., However, this tactic is yet to be developed at commercial scale., , 3. Improvement of plant resistance (Immunisation): Since plants do not have, antibodies like humans and animals, they cannot be immunized by vaccination. Through, genetic engineering however, scientists have successfully introduced and expressed in plants, genes from mice coding for the production of antibodies against viruses with which the mice, had been injected artificially., Inoculation of plants with some pathogens often results to temporary or nearly permanent, induced resistance (immunization) to a pathogen to which plants are normally susceptible., Induced or systemic acquired resistance (SAR) can be induced by treatment with chemicals,, such as salicylic acid, and dichloroisonicotinic acid and certain benzothiazoles., The resistance of plants can also be improved by genetic engineering technique. In this, method genes obtained from other plants, pathogens or other organisms (that code for the, production of enzymes, peptides or toxins for interfering with infection by the pathogen) are, incorporated in the desired plant. Plants developed in this way are called transgenic plants, resistant to a particular or more diseases., , 12.5- SUMMARY, Different types of harmful pathogens, weeds, pests and microorganisms are responsible for, plant diseases. Loss of crops from plant diseases may result in hunger and starvation,, especially in less developed countries where access to disease-control methods is limited and, annual losses are extremely high. To help decrease the loss done by various pests, weed and, pathogens, different methods of protections are being used. The principle of protection, involves placing a barrier between the pathogen and the susceptible part of the host to shield, the host from the harmful organisms., Plant protection measures are carried out to limit performance and yield losses in crop, production during the growing season and afterwards (storage protection) as well as for, quarantine purposes., Different types of plant protection methods like: physical, chemical, biological, biotechnical, and integrated methods help in protecting the plants from pathogens., Physical plant protection methods use both mechanical (tillage, flooding of fields, using, traps, fences etc.) and thermal means (hot water treatment, solarization) to control plant, pathogens., Chemical methods of plant protections involve mainly the treatment of soil, seeds, and foliar, sprays with fungicides, nematicides and other chemical products., UTTARAKHAND OPEN UNIVERSITY, , Page 279
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Biological methods of protection involve using organisms and their activity to protect plants, and enhance their resistance to biotic (harmful organisms) and abiotic limiting factors., Biological control of weeds primarily involved introducing beneficial organisms into new, habitats and introducing new pathogens which develop resistance in the host., Biotechnical methods include the use of light and colour traps, chemical attractants,, antibodies, pheromones, hormones, growth regulators for controlling harmful pathogens., Integrated methods aim at using natural limiting factors which can be achieved by reducing, use of chemical plant protection methods and simultaneously employing a variety of, measures from the other categories., Plant diseases can be controlled using different measures like: prophylactic, curative and, biological measures., Prophylactic measures involve avoidance, exclusion eradication, protection and therapy to, achieve protection of host plant from infection., Curative measures are used for treating diseased plants. Infections are cured using, thermotherapy, chemotherapy or tree surgery methods., Biological measures involve the use of different methods like: using antagonists for, eradication or reduction of the pathogen, direct protection of plants by antagonists and, immunization. Transgenic plants resistant to a particular disease can also help in controlling, many harmful diseases of crops., , 12.6- GLOSSARY, Abaxial directed away from the stem of a plant; pertaining to the lower surface of a leaf (see, adaxial)., Acute toxicityability of a single dose of a compound to poison (see chronic toxicity)., Aerification the act of infusing or forcing air into, for example, soil., Aerobic living only in the presence of oxygen., Antagonism a general term for interference between organisms that may include antibiosis or, competition for nutrients or space; action of two or more pesticides that reduces the, effectiveness of one or all (see synergism)., Antagonist an organism or substance that limits or counteracts the action of another, Antibiotic a chemical compound produced by one microorganism that inhibits growth or, kills other living organisms., Aphidsmall, sucking insect of the family Aphididae (order Homoptera) that produces, honeydew and injures plants when in large populations., Avirulence (avr) genegene in a pathogen that usually causes a hypersensitive reaction, is, associated with active plant defense reactions in a resistant plant, and causes disease in a, susceptible plant., Avirulent (syn. nonpathogenic) unable to cause disease (see virulent)., Avoidanceprinciple of plant disease control in which plants are grown at times or locations, where the pathogen is inactive or not present., Bactericide a chemical or physical agent that kills bacteria., UTTARAKHAND OPEN UNIVERSITY, , Page 280
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Bacteriocina protein antibiotic, one or more types of which can be produced and excreted by, certain strains of bacteria., Biocidea compound toxic to all forms of life., Biocontrol(syn. biological control) exploitation by humans of the natural competition,, parasitism and/or antagonism of organisms for management of pests and pathogens., Biological control(syn. biocontrol) exploitation by humans of the natural competition,, parasitism and/or antagonism of organisms for management of pests and pathogens., BiotechnologyTechnology based on biology by exploitation of biological processes to, develop technologies and products for the improvement of the life of mankind and our planet., Biotic relating to life, as disease caused by living organisms., Borer insect or insect larva that forms tunnels or cavities in the bark or within the wood of, trees., Certification seeds, propagative plant material, or nursery stock produced and sold under, inspection to maintain genetic identity and purity, freedom from harmful pathogens, insect, pests, and weed seeds. It is approved and certified by an official certifying agency., Chemical attractants insects or other arthrooods are attracted to animal and plant host, through chemicals either on contact or in air., Chemotherapy treatment of plant disease with chemicals (e.g. antibiotics or fungicides), absorbed and translocated internally., Crop rotationthe successive planting of different crop species; often used to improve soil, fertility or to reduce disease and pest problems., Cultural practicesthe manner in which plants are grown, such as: application of nutrients,, irrigation practices, type of cultivation; may be used for disease management., Disinfect to eliminate a pathogen from infected plant tissues., Disinfest to kill pathogens that have not yet initiated disease, or other contaminating, microoganisms, that occur in or on inanimate objects as such soil or tools, or that occur on, the surface of plant parts such as seed., Epidemicsspread of infectious disease to a large number of people in a given population, within a short period of time., Eradicationcontrol of plant disease by eliminating the pathogen after it is established or by, eliminating the plants that carry the pathogen., Fallow cultivated land kept free from a crop or weeds during the normal growing season, Fisheries a place where fish are reared for commericial purposes., Fungistat (adj. fungistatic) a chemical or physical agent that inhibits fungal growth,, sporulation, or spore geminiation, but does not cause death., Foliarpertaining to leaves., Fungistasisinhibition of fungal growth, sporulation, or spore germination but not death; used, to describe the nonspecific phenomenon in natural soils where spore germination is inhibited, and often overcome by rhizosphere nutrients., Growth regulator(syn. hormone) a chemical substance produced in one part of an organism, and transported in minute quantities to induce a growth response in another part, e.g. in, plants, auxins, cytokinins, and gibberellins., Herbicide a chemical used for killing plants or inhibiting plant growth, e.g. a weed or grass, killer., UTTARAKHAND OPEN UNIVERSITY, , Page 281
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Hormone(syn. growth regulator) a chemical substance produced in one part of a an organism, and transported in minute quantities to induce a growth response in another part, e.g. in, plants, auxins, cytokinins, and gibberellins., Host plantliving plant attacked by or harboring a parasite or pathogen and from which the, invader obtains part or all of its nourishment., Initial inoculum (syn. primary inoculum) inoculum, usually from an overwintering source,, that initiates disease in the field, as opposed to inoculum that spreads disease during the, season., Inoculum(pl. inocula) pathogen or its parts, capable of causing infection when transferred to, a favorable location., Mildewthin coating of mycelial growth and spores on the surfaces of infected plant parts., Nematicideagent, usually a chemical, that kills nematodes., Nematode nonsegmented roundworm (animal), parasitic on plants or animals, or free living, in soil or water., Prophylaxis treatment given or action taken to prevent disease., Protectant fungicide(syn. contact fungicide) a fungicide that remains on the surface where it, is applied; no after-infection activity (see systemic fungicide)., Protectant agent, usually a chemical, applied to a plant surface in advance of a pathogen to, prevent infection., Protection a principle of plant disease control in which a barrier is placed between the, susceptible plant and pathogen (e.g. the use of protective chemical dusts or sprays), Quarantine legislative control of the transport of plants or plant parts to prevent the spread, of pests or pathogens., Sanitation destruction or removal of infected and infested plants or plant parts;, decontamination of tools, equipment, containers, work space, hands, etc., Secondary inoculumsinoculum produced by infections that took place during the same, growing season., Seed treatmentapplication of a biological agent, chemical substance, or physical treatment to, seed, to protect the seed or plant from pathogens or to stimulate germination or plant growth., Susceptible (n. susceptibility) prone to develop disease when infected by a pathogen (see, resistance)., Systemic fungicidea fungicide that is absorbed into plant tissue and may offer some curative, or after-infection activity; includes fungicides that are locally systemic, xylem-mobile, (upward moving), and amphimobile (move in phloem upward as well as downward in the, plant) (see contact or protectant fungicide)., Systemic pertaining to a disease in which the pathogen (or a single infection) spreads, generally throughout the plant; pertaining to chemicals that spread internally through the, plant., Thermotherapy use of heat to reduce or eliminate pathogens in plant tissue; often used on, plants prior to meristem culture to produce pathogen-free plants., Tillagethe process of turning or stirring the soil., Toxicity capacity of a substance to interfere with the vital processes of an organism, Toxin poisonous substance of biological origin., UTTARAKHAND OPEN UNIVERSITY, , Page 282
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Transgenic (syn. genetically modified organism; GMO) possessing a gene from another, species; used to describe the organisms that have been the subject of genetic engineering., Trap cropcrop planted around a field to protect the inner crop from diseases transmitted by, aerial vectors; host crop of a parasitic plant, such as witchweed (Striga spp.), that is planted, to stimulate seed germination, and later sacrified by plowing under before the parasitic plant, produces new seeds., Trenchingphysical separation of soil in a vertical plane to sever grafted roots between trees., Virulence degree or measure of pathogenicity; relative capacity to cause disease., Virulenthighly pathogenic; having the capacity to cause severe disease (see avirulent)., Virusa submicroscopic,intracellular, obligate parasite consisting of a core of infectious, nucleic acid (either RNA or DNA) usually surrounded by a protein coat., , 12.7- SELF ASSESSMENT QUESTIONS, 12.7.1 Objective questions:, 1. Prophylactic measures means(i) protection of host plant from infection, (iii) protection of plant from draught, , (ii) protection of host plant from pollution, (iv) none of the above, , 2. The principle of avoidance involves(i) Choice of time of planting, (iii) Both (i) and (ii), , (ii) Choice of geographic area, (iv) None of the above, , 3.Application of which nutrient in the soil is required for new vegetative growth, and delayed, maturity(i) Nitrogen, (ii) Zinc, (iii) Boron, (iv) Iron, 4. The antibiotic becteriocin that inhibits the growth of Agrobacterium tumifaciens in Crown, gall disease is(i) viridian, (ii) agrocin 84, (iii) bt 43, (iv) none of the above, 5. SAR means(i) Systemic Advance Reaction, (iii) Systemic Acquired Reaction, , (ii) Systemic Adverse Reaction, (iv) None of the above, , 6. The antagonistic plant that is found useful in controlling nematodes in Tomato(i) Bouganvillia, (ii) Marigold, (iii) Asparagus, (iv) None of the above, 7. A hyperparasite that controls soil borne diseases caused by fungi(i) Trichoderma spp., (ii) Bacillus spp., UTTARAKHAND OPEN UNIVERSITY, , Page 283
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , (iii) Rhizopus spp., , BSCBO-101, , (iv) None of the above, , 8. Individual preventive methods taken for plant protection(i) Site design, (ii) Crop rotation, (iii) Both (i) an (ii), (iv) None of the above, 9. Factors that control plant disease are(i) Soil management, (iii) Rotation of crops, , (ii) Selection of disease resistant plants, (iv) All of the above, , 10. Soil solarization is a noval method of soil treatment to destroy(i) Fungal spores, (ii) Nematode propagules, (iii) Both (i) and (ii), (iv) None of the above, , 12.7.1 Answer Key, 1-(i), 2-(iii), 3-(i), 4-(ii),5-(iii),6-(ii),7-(i), 8-(iii), 9-(iv),10-(iii), , 12.8- REFERENCES, , , , Agrios G. N , 2012. Plant pathology3E Elsevier, p-201-2010., Altman J and Campbell CI, 1997.Effect of herbicides on plant diseases.Annu. Rev., Phytopath. 96:140., , , , CharudattanR, and Walker H. L (Eds). 1982. Biological control of weeds with plant, pathogens. Wiley, New York., Curl E. A 1963.Control of plant disease by crop rotation. Bot Rev. 29: 413., , , , , , , , , , , , , , De Wit PJGM 1997. Pathogen avirulence and plant resistance : a role for recognition., Trends Pl.Sc. 2: 452., Hornby D (Ed.) 1990. Biological control of soil-borne plant pathogens. CAB, International. Wallingford, Johnsan R and Jellis G. J (Eds). 1959-1960. Breeding for disease resistance. Kluwer,, Hingham, Massachusetts., Khan Aslam, Plant diseases Gyan publ. house p 69-90., Oerke E. C, DehneHw, Schonberg F and weber A 1994. Crop protection and crop, production. Elsevier, Amsterda., Sharma P. D, 2004. Plant pathology Rastogi Public.p-107-161, Singh R. S 1998. Plant diseases 7th ed. Oxford and IBH Publish.Co. New Delhi., Singh R. S, 1984. Introduction to principles of plant pathology 3rd ed. Oxford and IBH, Publish.Co. New Delhi., Stapples R. C (ed). 1981. Plant disease control: resistance and susceptibility. Wileyinterscience New York, Stirling G. R, 1991.Biological control of plant parasitic Nematodes. CAB Int. Chichester,, Uk, , UTTARAKHAND OPEN UNIVERSITY, , Page 284
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , , , , , Tar S. A. J 1972. Principles of plant pathology Macmillon Press. London., Van der Plank J. E 1984.Disease resistance in plants 2nd ed. Acad. Press London., Walker J. C 1968. Plant pathology 3rd ed. McGraw Hill, New York., , , , Zadoks J. C and Schein R. D, 1979.Epidemiology and plant disease management.Oxford, Univ. Press. London, , 12.9- SUGGESTED READINGS, , , Singh R. S, 1984. Introduction to principles of plant pathology 3rd ed. Oxford and IBH, Publish.Co. New Delhi., , , , , , , , 10. Walker J. C, Plant Pathology, McGraw Hill, New York., 11. Ravichandra N. G Fundamentals of Plant pathology, McGraw Hill Ind.Pvt.Ltd., 12. Neil H, Nigel C, Kevin B, 2014, Biological control in plant protection: a colour, handbook, 2nd Ed. CRC Press., 13. Jr. Roger B Yepsen, 1976. Organic plant protection, Rodale Pr., 14. Charles Vincent,2001 Physical control methods in plant protection. Springer., , , , , Singh RS 1998. Plant diseases 7th ed. Oxford and IBH Publish.Co. New Delhi., Sharma P. D 2004, Plant pathology. Rastogi Publ. Meerut, India., , , , Sambamurty A. V. V. S 1992, A Text Book of Plant Pathology, I K International Pvt., Ltd., Mehrotra R. S and Agarwal A, Fundamentals of plant pathology, PHI Learning., Hariday S, Chaube R. S, Introductory Plant Pathology, CBS., Agrios G. S, Plant Pathology, Academic Press, London., Holton CS, Plant Pathology: Problems and Progress 1908-1958, MaddisonUniv,, Wisconsin Press., Stakman E. C, Harrar, J. G, Principles of Plant Pathology, Ronald Press, New York., , , , , , , , 12.10- TERMINAL QUESTIONS, Q1. What do you understand by Plant protection? Explain briefly the various methods, employed in plant protection., Q2. How can we control a spread of disease in plants? Give brief notes on Prophylactic, measures of control., Q3. Explain briefly the various techniques of Biocontrol of plant diseases., Q4. What are the different types of chemical measures taken for control of plant pests,, pathogen and insects?, Q5. How can plant protection help in reducing crop loss done by pathogens?Briefly describe, the process and measures of plant protection., Q6What are the Curative measures used in control of plant diseases?, Q7. How can antagonists help in eradication or reduction of the pathogen inoculums?, UTTARAKHAND OPEN UNIVERSITY, , Page 285
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MICROBIOLOGY, MYCOLOGY AND PLANT PATHOLOGY, , BSCBO-101, , Q8. What is Chemotherapy? How can it help in controlling plant disease?, Q9. What is Immunisation? How can it help in treatment of pathogens?, Q10. Answer the following(i) Name two Nematicides., (ii) Name two non-conventional chemicals used for disease control., (iii) Name two antibiotics used in disease control., (iv) Name two chemicals used for seed treatment., Q11. Write short notes on:, (i) Trap plants, (ii) Antagonistic plants, (iii) Quarantine regulations, (iv) Environmental impact, , UTTARAKHAND OPEN UNIVERSITY, , Page 286
