Modifications in handling of segregating generations
- 4. Procedure of pedigree method Sudha's KSM 95
- 5. MERITS OF PEDIGREE METHOD: • Breeder use skill and judgement for max. extent in early segregating generations. •Improvement of easily identified and simply inherited characters. •Transgressive segregants. •Less time than bulk method. •Pedigree record – any time information. •Plants and progenies with defects and weakness are eliminated at earlier generations – save resources and time. Sudha's KSM 95
- 6. DEMERITS OF PEDIGREE METHOD • Maintenance of pedigree record. • Selection among and with in a large no. of progenies in every generation is laborious. • No natural selection. • Selection for yield in F2 and F3 ineffective. Sudha's KSM 95
- 7. • Basic tenet- carry forward F2 plants as random bulk of each family till later generations where standard pedigree method can be started. Sudha's KSM 95
- 8. • Harrington (1937). • One of the earliest modifications where single plant selection is delayed till a favourable environment for the expression of character is encountered. • Bulked progenies if environmental conditions do not ensure optimum expression of the character. Sudha's KSM 95
- 9. • RICHMOND (1951) in cotton. • For maintaining the genetic variation in bulk progeny of primary selections made in F2. • Till the families attain sufficient homozygosity and their performance is tested over a period of time. • In highly self pollinated crops F2 plants are visually selected and their seed grown in replicated, usually twice. • F3 seed scored for yield performance are bulked and harvested and put in replicated yield trail in F4. Sudha's KSM 95
- 10. • Frey (1954) carried forward F2 plants to F5 generation as individual families taking each family as a line entry in nursery trials. • No selection within lines up to F5, but from F6. F2 PROGENY METHOD: • Lupton and Whitehouse (1957). • Where F2 plants are selected for easily determined characters. • The F3 progenies are again selected on the same basis without any selection within families and harvested as individual bulk progenies. • The yield trial and quality test is conducted on these F4 bulk progenies rather than on F3 progenies as proposed by Frey (1954). • The same test is repeated in F5 and F6 which provides information on important characters including yield to reduce the number of lines. Sudha's KSM 95
- 11. • Single plant selections are made in F7 generation for further evaluation in yield trials in subsequent generations. • Hyne and Finney (1965) also described a modification which in fact was used by Nilsson-Ehle in 1909 where selection is performed in F2 and among F3 lines after which sufficient bulk seed becomes available to evaluate traits like yield in F4 generation. • So all these methods are especially similar but differ only with respect to the generation in which individual plant selections and replicated yield tests are initiated. Sudha's KSM 95
- 12. • The pedigree trial method of Lupton and Whitehouse (1957). • Provides combination of yield trails and pedigree selection. • F2 selected for qualitative characters. • F3 progeny rows are space planted. • Like conventional pedigree method the best F3 progenies are identified from which single plants are selected, as in F2, and sown as progeny rows in F4 generation. • One or more of these F4 rows of each progeny are used for pedigree selection and remaining rows of each progeny are bulked separately for yield trial in F6 generation. Sudha's KSM 95
- 13. • So, obviously the seed for yield trail in F6 comes not from yield trial of F5 but a new, albeit, superior bulk is obtained from rows kept for pedigree selection. The same procedure is repeated in F7 generation. • In this way in each successive generation the seed used for yield trial is gradually improved for yield potential and becomes uniform, homozygous and more similar to the corresponding progeny rows with the result that no further selection is required after the series of trails have been completed. • Since the yield data from three year trails in F5,F6 and F7 becomes available by F7 so best lines can be multiplied for final yield trials saving at least two years by speeding up the breeding programme. Sudha's KSM 95
- 14. • The inherent weakness of this procedure lies in carrying forward each F3 derived line through a single culture i.e. progeny of only one line for detailed pedigree selection, the rest of the cultures being bulked for yield trails. • Voight and Weber (1960) proposed selection go F2 plants to raise F3 progeny rows. Three good plants from each of the progeny are selected to get F2 derived F4 families. These three family lines are separately entered in yield trails in F4 , considering each line as a replication thus leading to three replications of an F4 family. • The best families are identified on the basis of average of three replications from which single highest yielding line is retained to represent the family for forth coming F5 test. An early derivation of lines i.e. in F4 is attractive but a uniform selection of three plants from each F3 progeny out of which progeny of only one is to be retained in F4 appears to be too restrictive. Sudha's KSM 95
- 15. • Two pronged selection system in which the first step involves the identification of promising F2 plants from which then extensively selection is conducted. Styne (1968) proposed that superior families can be identified from the performance of random lines derived from the families. • Iver and Fehr (1978) used this concept to describe a procedure in which a number of F2 plants are randomly taken and bulk progeny from each plant (family) are selfed or as such advanced for several generations until an acceptable level of homozygosity is achieved. • An individual homozygous plant is then randomly taken to represent a family in yield trials to be performed next year. Sudha's KSM 95
- 16. • The remnant seed of F2 plant i.e. F3 family stored in reserve whose individual plant progeny pure line survived the yield test is taken for further selection to develop new cultivars. Even the line pure line used to predict the family performance also can be released as a cultivar if its performance is satisfactory. • Richmond’s (1951) bulked progeny test system also provides for such a retroactive selection from selfed seed of F2 plants whose bulked progenies have survived the replicated yield trial up to F6-F8 generations. • The PLF is essentially a screening method aimed to identify productive foundation F2 plants without any selected can be helpful to eliminate low yielding lines prior to the isolation of pure lines. More than one pure lines can be used to give a broad representation of the F2 family but it would reduce the number of F2 families that can be evaluated. Sudha's KSM 95
- 17. • Realizing the ineffectiveness of single plant selection in F2, Valentine (1984) suggested that more emphasis should be laid on F3- line evaluation. He proposed a scheme for rapid generation advance to the point of testing F3 lines in cereals. The crosses are made in green houses and F1 seed is grown in green house in the same season to produce F3 embryo seed. In the second season F3 progenies are grown in the field during normal season. • After this it takes the time of conventional pedigree method and saves one year. Valentine (1984) considered it to be highly suitable for highly bred materials whereas it would be less effective for crosses of adapted x unadapted lines where high discard rate is required Sudha's KSM 95
- 18. Sudha's KSM 95
- 19. • Crosses and plants likely to produce superior progeny are identified at early stages say in F2,F3,F4. • Main objective: select 1. superior crosses. 2. superior plants with in superior crosses. Sudha's KSM 95
- 20. • Evaluation of F2,F3 or F4 bulks. Performance i.e. yield of F2,F3,F4 bulks from different crosses gives some information about the performance of progenies derived from them. This information would be more reliable if yield trials were conducted at more than one location in two or more years. Poor yielding crosses are generally less likely to produce better yielding progenies than the higher yielding ones. Early generation bulk tests may, therefore, help the breeder in discarding poor crosses and allow him to give more attention to superior ones. Sudha's KSM 95
- 21. • Grid method: • Honey comb design: • Indirect selection: • Visual selection: • Evaluation of F3 and F4 progenies a.Contiguous Control b.Moving Average Sudha's KSM 95
- 22. Bulk method The bulk method of breeding was first used by Nilsson- Hele in 1908. In the bulk method, F2 and the subsequent generations are harvested in mass or as bulks to raise the next generation. At the end of bulking period, individual plants are selected and evaluated in a similar manner as in the pedigree method. Applications Isolation of homozygous lines. Waiting for the opportunity for selection. To provide opportunity for natural selection to change the composition of the population. Sudha's KSM 95
- 23. Schematic representation of Bulk method Sudha's KSM 95
- 24. Merits The bulk method is simple, convenient and inexpensive. Artificial or natural disease epiphytotics, winter killing etc. eliminate undesirable types and increase the frequency of desirable types. The isolation of desirable types thus becomes much easier. Natural selection increases the frequency of superior types in the population. Progenies selected from long term bulks are likely to be for superior to those selected from F2 or short term bulks. Little work and attention is needed in F2 and subsequent generations. No pedigree record is to be kept, which saves time of labour. Transgressive segregants are more likely to appear and increase in frequency due to natural selection. Artificial selection may be practiced to increase the frequency of desirable types. It is suitable for studies on survival of genes & genotypes in populations. Sudha's KSM 95
- 25. Demerits Intakes longer time to develop a new variety. In short-term bulks, natural selection has little effect on the genetic composition of populations. It provides little opportunity for breeder to exercise his skill or judgment in selection. A large number of progenies have to be selected at the end of the bulking period. Information on the inheritance of characters cannot be obtained. Sudha's KSM 95
- 26. Single seed descent method • This is modified from bulk method. • In this method a single seed from each of one or two thousand F2 plants is bulked to raise the F3 generation. • Similarly, in F3 and subsequent generation one random seed is selected from every plant present in the population followed till F5 or F6 when plants would have become nearly homozygous. • In F5 or F6 large number individual plants are selected and individual plants progenies are grown in next generation. • Individual plants are selected from outstanding families showing segregation. Sudha's KSM 95
- 27. merits • This is simple, convenient, less expensive and time saving method. There is no need to keep much record. • Large number of crosses can be evaluated by this method, because less space and labour is required in each generation. • This method is able to retain considerable variability in a breeding population. • The material can be rapidly advanced by growing the same in green house. Sudha's KSM 95
- 28. Demerits • This method does not provide opportunity to practice selection for superior plants till F5 generation superior plants may lost. • The frequency of getting desirable in the advanced generation is reduced. • Identity of superior F2 plants cannot be maintained. • This method is more useful when more generations can be grown per year. Sudha's KSM 95