Pedigree Method of Breeding
Pedigree Method of Breeding
Pedigree method of breeding has been used most widely for the development of varieties in self pollinated crops. In this method, desirable but diverse parents are first selected and crossed, F1 generation is then raised and seeds of F1 plants are collected. All the F1 plants will be highly heterozygous and, upon selfing will release lot of variability in the F2 generation. Individual plant selections are initiated from F2 itself, particularly for qualitative characters like disease resistance. Such individual plants selected in F2 generation are advanced to F3 generation through separate individual plant progeny rows and selection within and between progeny rows is continued in the later generations upto F5 and F6, till the segregation is available. However, after F4 emphasis will shift towards selection of progenies rather than individual plants. Later, when no segregation is observed within progeny rows, selection is done only between the progenies, because selection within progenies of the same plant will be futile, there being no variability. A proper pedigree record of all the selected plants is maintained so that breeder is able to avoid selecting too many closely related pedigree lines of each selected F2 plant. Pedigree record can also give a general idea about inheritance of simply inherited characters.
Procedure of Pedigree Method
Different steps involved in pedigree method are described year-wise in the following steps-
First year (crossing the parents)-
Parents are chosen for hybridization on the basis of genetic diversity. This is a very important step because the success of programme is based upon correct choice of both the parents. If they are related and not diverse, much progress cannot be achieved. Such desirable parents are crossed and F1 seed is produced.
Second year (F1)-
F1 plants are space planted so as to obtain sufficient quantity of F2 seed for raising the next generation (space plantation allows better growth, more tillering and hence more seed).
Third year (F2)-
In F2 generation, about 2000-10,000 plants are raised under space planted conditions. About 200-500 plants are selected which should have desirable major genes, like those for resistance to diseases etc, and should also have a high intensity of other desired characters for the new variety to be developed. The seed harvested from each selected plant is kept separately for raising the next generation.
Fourth year (F3)-
Seed of each selected plant from previous generation is space-planted in plant to row progenies and the number of plants in each progeny row is kept 30-100. Individual plant selection for desirable characters are done within progeny rows as well as between different progeny rows. The seed of each selected plant is kept separately to be sown as progeny rows next year.
Fifth year (F4)-
Plant to row progenies are grown from F3 selected plants. Individual plant selection is done in the same way as in the previous generation, but more emphasis is laid on selecting plants from best progenies rather than selecting plants from the same progeny. This is possible and desirable because a fairly high level of uniformity within progeny rows appears in this generation (F4) due to increased homozygosity.
Sixth year (F5)-
The Plants selected from F4 generation are generally grown according to commercial planting rates and preferably three or four rows of each progeny are grown to have better comparisons among progenies. All the plants of a progeny showing uniformity and best performance among different progenies are bulk harvested for testing in the preliminary yield trial.
Seventh year and onwards-
In F6 generation, normally segregation does not occur. But if some progenies which are not promising and still show segregation, they are rejected. However, if a segregating progeny is very promising, individual plant selection is done even in F6 generation as in the previous years. Promising progenies showing uniformity are bulk harvested and tested in replicated yield trials alongwith suitable check varieties. Afterwards, superior progenies giving good yields are evaluated over several locations for three to five years. The strain which consistently performs better than the best available varieties, over a wide range of localities is released as a new variety.
Merits and Demerits of Pedigree Method
Pedigree method of breeding takes less time (relative to bulk method) and is the most suitable method where individual plant selection is practised, after hybridization. It is a suitable method both for the simply inherited characters and also for the quantitative traits like yield, although selection for yield is not possible in early generations. For this reason it is most widely used for breeding self-pollinated crops.
However, the pedigree method is sometimes regarded as cumbersome, since pedigree records are to be maintained which means enough time and effort. Further, the natural selection does not play any important role and selection depends mainly upon the skill of the breeder. Particularly the selection in early generations (F2, F3) is difficult since plants are heterozygous and may not lead to desirable progenies. In these early generations, some useful plants may also be rejected for the same reason.
Achievements of Pedigree Method
Pedigree method has been the main method of breeding for varietal development programme in self-pollinated crops. Therefore, a number of varieties have been developed using this method in several crops like wheat, rice, pulses, barley, oilseeds, tobacco, vegetables, etc. Some of the important varieties include K 65, K68, WL711 and those belonging to N.P. series for wheat; Jaya, Padma, Bala, Ratna for rice and Pulse Early Dwarf for tomato.
- Interaction of Genes- Complimentary, Epistatic, Duplicate Gene etc.
- Inheritance of Multiple Factors
- Linkage- Types, Linkage Groups, Importance
- Concept of Crossing Over- Types, Mechanism, Significance
- Mutation- History, Range, Types, Stages etc.
- Aneuploidy- Monosomy, Nullisomy, Trisomy, Tetrasomy
- Procedure of Hybridization in Plant Breeding
- Selection Method of Plant Breeding
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