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16, Pedigree Selection, , % hol, , 16.1. INTRODUCTION, , Mass»and«pureline»selections “Chapters (14 and 15) are applied-to=genétically~variable and, homozygous-populations. However, these, methods, cannot beapplied’to'segregating populations,, e.g., Fo, F3, etc., obtained from crosses. T. e-methods. generally. used for handling of-segregating, generationssare, (19 pedigree-methodr( bulkemethod;and-(3).backcross:method. The: pedigree, method=w: t-outlined. by Li 1927.'In this method, individual-plantsyare’selected from, Fyand’subsequent.generations, their-progeniesate grown, and a record.of all the parent-offspring ye, relationships=is= maintained. eT a ace ee we, Virtually Gomozygous) and they-s! io. segregation) atsthis:stage;.selection'is done-among the, progenies -because there-would be negligible genetic variation within-the: progenies. ane, , , , , , , , , , ’, , 16.2, PEDIGREE RECORD ', In pedigree method, a detailed.record. of. the relationships" between»the:selected:plants:and their, Progenies:is-maintained; such=a=tecord-is:knownas*pedigree:record or simply Pedigree. As 2, result, each progeny in every generation can be traced back’ to the Fy plant from which it, Originated. The-pedigree is helpful-in-finding_o ut if: two-indivi ed_by descent, i.e.,, have a common parent in their ancestry, and therefore are likely to have some alleles in common., Pedigree record may be maintained in several different ways, but it should be simple and accurate., Generally, each-cross.is-given-a-number; the first:two digits of this number refer to the: yearsin, Which the-cross-was:made, and the-remaining. digits denote the serial number of the cross-in-that, year. For example, the number 7911 denotes cross number 11 of year 1979. In the segregating, 8enerations, one of the following two systems of designation ma, , y be. followed., __. XL. Designation Based of the Location of Progeny Rows in the Field. In this system, individual plant progenies \in F3 and later generations are assigned row numbers corresponding, , to their location in the plot. In addition, each Progeny in Fy and later generations is assi gned the, , Scanned with CamScanner

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. 235, pedigree Selection i, , TABLE 16.2. System of designating individual plant progenies by serial numbers assigned ., to the selected plants :, , , , , , Generation Progeny number Description, Fy 791-7 Progeny obtained from plant number 7 selected in Fz ;, Ky 7911-7-4. Progeny from plant number 4, selected from the F3 progeny derived, , from plant number 7 selected in F, , Fs 7911-7-4-2 Progeny from plant number 2, selected from the F, progeny derived, from plant number 4 selected from the F; progeny obtained from plant, number 7 selected in Fy, , Fe > 7911-7-4-2-8, , Progeny: from plant number 8, selected from the F's; progeny derived, from plant number 2 selected from the F, progeny of plant number 4, selected from the F, progeny of plant number 7 selected in Fy, , 3. The pedigree record must be accurate. Kee, , ping no record is better than keeping an inaccurate, record, which will only create confusion. . ., , The pedigree record is often useful in elimination of some progenies. In later generations,, e.g., Fs, Fe; etc., if some lines originated from the same F, or F3 progeny and are similar, only, one of these may be maintained. Further, it may often be possible to obtain a general idea about, the inheritance of characters by studying the pedigree record., , 16.3, APPLICATIONS OF PEDIGREE METHOD, , Pedigree method is the ‘ only-used. method. for. selection -from-segregating-generations, of.crosses offSelf-pollinated-crops> his:method:is:often-used to correct:some:s; ecific weaknesses, of:anzestablish iety (combinatio: reeding). Pedigree*method-is-also-useful for selection-of, , pes) including transgressive™segregants (transgressive breeding),, t le: for-improving. specific characteristics, such as di, Plantsheight, maturitystime, etc., as ‘wellnas.-yield-and- quality. characteristics, , objective of thé breeder is to correct specific weaknesses of a va, improve yield and quality as well., , , , , Se resistance,, ven when the, , riety, he generally excepts to, , , , 16.4. PROCEDURE FOR PEDIGREE METHOD *, , A general outline of the pedigree method is given below (Fig. 16.1), but the breeder may modify, it according to his specific needs. : ‘ ‘, , 1. Hybridization. Selection of parents (Séction 16.6, important step in a breeding programme based on hybridiza, to produce a simple or a complex cross. For convenience, w, both simple and complex crosses as F; seed., , ) to be used in a cross is the most, tion.The selected parents.are crossed, € shall refer to the seed obtained from, , 2. F, Generation. Fy ‘seeds:arespace-planted.so:that-each-F-plant roduces ibe :, Tumber-of::F>-seed. Ordinarily, 15-30 F, plants should produce vere _, , enough. seed fi 2, Populations size. Bh seed fora good Fy, , 3. F, Generation. In Fy,'2,0, , os ed separately, U: i, $12¢ should be 10-100 times the number of, F> plants tf Habe ee Population, , hat would be selected, i, Fy progenies that can be handled. This number may riccted, ie., the number of, , vary from 100 to 500 depending on the, , Scanned with CamScanner

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Plant Breeding : Principles and Methog, , 236, , , , Selected parents’ planted in-a crossing block and, , crosses are made ., , , , , , , , , , FIRST: Ei, FIRST PARENTS, , d harvested jn, , , , , , 40-30 seeds are space-planted; see, , , , , , , , , , , , , , , , , , SECOND ~-Py*, YEAR + a ? bulk, ( -planted, (9 2,000-10,000 plants space-p!, ERR os oF (i 100-500 superior plants selected, FOURTH | 4 * (Individual plant progenies space-planted, YEAR Fs. rene (i) Superior plants selected from superior progenies, BETH. Fy: HUUUUIPILLNIL 45 artrane 3, : 4 -) individual, plant progenies planted in. multi-row, coo SOE rg WPI. los ct, (i) Superior plants selected from superior progenies., SEVENTH : () As in (i) and (i) in F, sty, YEAR Fe I Il Ih I Ml il Il (i) Preliminary yield trial may be conducted, , — =>, , _ EIGHTH : . . (i) Preliminary yield trials, : Fy ; 0 LO Oo (i) Quality tests., , "YEAR, ea Fa-Fio A A 5 = ( Coordinated yield trials, YEARS | (i) Disease and quality, tests, , , , TWELFTH Fy Seed increase for distribution begins., , - YEAR, , , , , , , , , , , , Fig. 16.1. A simplified schematic representation of pedigree desthon, , facilities-available and objectives of the breeding programme. When’closely:related varieties af, crossed,-the number of F5"progenies maintained would-be-considerably smaller than*when the, parents are’unrelated:by. descent. When the objective of breeding is to improve yield, a relatively, larger number of F plants would be selected. ; :, , Selection in Fy is based on characteristics that are simply inherited, ae, plant height, head, type, seed colour, disease resistance, presence of awns, etc. Selection for vigour is genera y, polenta er jan be due to heterozygosity, environment or GxE interaction. Selection, fas roneaut ee and a are generally ineffective because they are greatly affected by, because he has to jud 2 which - value of selection will largely depend upon the skill of breede’, eee os tact ae ich F plant would produce superior progeny for characters like yiel, , eritability. A breeder develops this skill through a close and deep study of the, , concerned crop species. It may be em, i i, . phasized that the breeder ad, as he can handle efficiently in the subsequent generations. Carte ei coe ‘, , Scanned with CamsScanner

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Pedigree Selection ag ye TY 237, , , , 4. F3. Generation. Individual=plantsprogenies:having~30 "or more»plants-each-are-spaceplanted. Individualplants=with:desirable:characteristics-aresselected, . particularly-from superior, progenies. Outstanding plants from inferior progenies fnay also be selected. Disease and lodging, susceptible progenies and those with undesirable characteristics are eliminated: The number of, , plants selected in F3 should preferably be less than that of the F; progenies. If the number of, superior progenies is small, the whole cross may be rejected., , 5. F4 Generation. Individual plant progenies are space-planted, and desirable plants are, selected mainly from superior progenies. The number of plants selected in F, is genérally much, smaller than that in F3. Progenies with defects and undesirable characteristics are rejected. If two, or more progenies coming from the same F; progeny are similar and comparable, only one of, them may be saved. Thus the emphasis is on selection of desirable planis from superior progenies., , 6. Fs Generation. Individual plant progenies are generally planted according to the, recommended commercial seed rate. Often three or more rows are grown for each progeny to, facilitate comparison among progenies. Many progenies would have become. reasonably, homozygous and may be harvested in bulk. In progenies showing segregation, individual plants, may be selected. The breeder has to visually assess the yielding potential of progenies and reject, the inferior ones. The number of progenies must be reduced to a size manageable in preliminary, yield trials, i.e., about 25-100 progenies., , 7. F¢ Generation. Individual plant progenies are planted in.multi-row plots and evaluated, visually. Progenies are harvested in bulk since they would have become almost homozygous., Progenies showing segregation may be eliminated unless they are outstanding; in such progenies, individual plants may be selected. Preliminary yield trial is usually planted in Fe for those, , _progenies, which are reasonably homozygous and have enough seed. Inferior progenies are, eliminated based on yield data from preliminary yield trial and/or visual evaluation., , 8. F, Generation. Preliminary yield trials. with three or more replications are conducted to, identify few superior lines. Standard commercial varieties must be included as checks for, comparison. The progenies are evaluated for plant height, lodging and disease resistance, flowering, time, maturity time, etc. Quality tests may serve as additional criteria for selection. Two to five, outstanding lines, if superior to the checks, would be advanced to the coordinated yield trials., , 9. Fs to F149 Generations. The superior lines are tested in replicated yield trials at several, locations. These lines are evaluated for yield, disease and lodging resistance, maturity time and, quality, etc. A line that is superior to the best commercial variety(ies), included in the trial as, check, in yield and other characteristics will be identified for release as a new variety., , 10. F,; Generation. When a strain is likely to be released as a variety, the breeder usually, multiples its seed during its last year in trial. The breeder thas the responsibility to. supply the, breeder’s seed for production of foundation seed. Thus in Fi, to Fj the. seed of the new variety, will be multiplied for distribution to the farmers. i :, , 16.5. SELECTION OF PARENTS, , Selection of parents for hybridization is the most critical step in a breeding programme and this,, step decides the type of progeny that can be obtained. As a rule, all the characters-sought to be, improved, in the variety to be developed,'must be present in-one or the other parent because the, alleles not present in the parents of a cross will be absent from their progeny. Obviously, the, choice of parents depends on the objectives of the-breeding programme. Selection of parents for, , Scanned with CamScanner

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pedigree Selection _ 251, , , , 16.11. OFF-SEASON CROPS, , The time needed for developing a variety may be reduced-if off-season crops are grown at, suitable locations. F, generation may be safely advanced to F, in greenhouse or in an off-season, nursery. Segregating populations may also be advanced in case they are bulked. The land and, other facilities at off-season nurseries or in a greenhouse are generally limited so that it may not, be possible to grow a large number of progenies. Off-season nurseries or greenhouses cannot be, used for making selections, except for simply inherited characters, because the prevailing, environment would generally not be comparable to that at the place for which the variety is being, deyeloped. An off-season crop of wheat, barley, etc. may be grown at Wellington (T.N.); of rice, at Cuttack (Orissa); two off-season crops of maize at Dholi (Bihar) and Varanasi (U.P.); of pulses, , at Sangla (Kinnaur) and Lahaul Spiti (H.P.); of gram at Taper-Waripore (J.K.); and of linseed and, Brassica at Kukumseri (H.P.)., , 16.12. MERITS OF PEDIGREE METHOD., , 1. This method gives=the=maximum=opportunity»forsthe™breeder=to»usehis~skill and, judgement® for selection of desirable Plants, particularly in the early segregating, . generations., , , , 3. Trangesive-segregants for yldand oe guiniaive Charters my be recovered, , in addition to the improvement in specific characters., 4. an=the-bulk=method.to.develop-anew variety., . The breedermay-often be able:to-cbtain-information-about the inheritance of qualitative, , characters*from*the" pedigree record. —, 6. Plants and progenies with visiblexdefects*and weaknesses;are-eliminated:atvanvearly, , stagesinsthe=breeding "programme; this saves resourcés and the time of breeders., , 16.18. DEMERITS OF PEDIGREE METHOD, 1. Maintenancerof ‘accurate pedigree records takes up:waluable time. Sometimes it may be, , a limiting factor in a large breeding programme., , 2. Selection among and within a large number of progenies in every-generation:is laborious, andstimesconsuming; this»limits:theenumbersof:crosses-a‘breeder-can- handle., _-4-The success:ofsthis-method-largelysdepends. on. skill. of the breeder., 4. There is no.opportunity..for-natural’selection=to-influence*the*populations., 5. Selection for yield in F, and F is ineffective. If care is not taken to rétain a sufficient, number of progenies, valuable genotypes.may be lost in the early segregating generations., , , , , , 16.14. ACHIEVEMENTS, , ‘Once the genetic variability present in desi varieties was exploited, hybridization was used for, further i improvement in the various crops. Pedigree method has been’ the most extensively used, method for handling of segregating generations from crosses, and a large number of varieties, have been developed in crops like wheat, rice, barley, pulses, oilseeds, cotton, tobacco, sorghum,, Vegetables, etc. Nearly all the improved varieties of self-pollinated crops recommended for, Cultivation today have been developed by this method. These varieties ‘Tepresent improvements, in yielding ability, quality, disease resistance and other agronomic characteristics., , Scanned with CamScanner