Author: SANDEEP KUMAR BANGARWA
- Recurrent selection :- Method which involves reselection generation after generation with interbreeding of selects to provide for genetic recombination. Thus it is a cyclic selection that is used to improve the frequency of desirable alleles for a character in a breeding population.
- Term coined by Hull (1945) & procedure described by Jenkins (1940).
- Suggested by Hayes & Garber (1919) & East & Jones(1920).
- First detailed description of this type of breeding method was published by Jenkins in 1940 as a result of his experiments with early testing for GCA in maize.
- The goal of recurrent selection is to improve the mean performance of a population of plants; a secondary goal, but nevertheless very important, is to maintain the genetic variability present in the population to the extent possible.
- Progress in selection is based on the heritability of the trait and the types of genetic variation controlling the trait in the particular population under selection and on the selection differential.
- Recurrent selection was originally developed as a method of breeding in cross pollinated species. Now it is also used in self pollinated species. However, it is more commonly used in cross pollinated species than in self pollinated species.
- The source material may be random mating populations, synthetic cultivars, single cross, or double cross. The improved population may be released as new cultivar or used as a breeding material (parent) in other breeding programmes.
- Recurrent selection may be used to establish a broad genetic base in a breeding programme because of multiple opportunities for intermating , the breeder may add new germplasm during the procedure when the genetic base of the population rapidly narrow after selection cycles.
- Recurrent selection is superior to classical breeding when linkage disequilibrium exists.
- The most desirable outcome of recurrent selection is that the improved population is produced without reduction in genetic variability. In this way, the population will respond to future improvement.
- Without use of tester (Simple recurrent selection) the scheme is effective for only traits of high heritability. Hence, only additive gene action is exploited in the selection for the trait.
- Where testers are used, selection for GCA and SCA are applicable, permitting the exploitation of other gene effects.
- Conclusion on the efficiency of different Recurrent selection Schemes (When epistasis, multiple alleles and linkage disequilibrium are absent)
1. If dominance is incomplete ( RS-GCA = RRS > RS- SCA)
2. If dominance is complete the three methods are equal ( RS-GCA = RS-SCA = RRS)
3. If overdominance is present ( RRS = RS - SCA > RS – GCA) - When epistasis, multiple alleles and linkage disequilibrium are present then RRS would be superior to RS-GCA and RS-SCA.
- In almost all practical situations, RRS would be superior to RS-GCA and RS-SCA.
- Recurrent selection is an important method of population improvement.
- Recurrent selection is a modified form of progeny selection.
- Recurrent selection is differs form progeny selection in following aspects :-
| S.NO. | Recurrent Selection | Progeny Selection |
| 1. | Selected plants are self pollinated | Selected plants are open pollinated |
| 2. | Progeny of selected plants are intermated in all possible combinations. | Progeny of selected plants are open pollinated. |
- Types of recurrent selections
2. Recurrent selection for GCA
3. Recurrent selection for SCA
4. Reciprocal recurrent selection
1. Simple Recurrent selection
- Simple recurrent selection is the simplest form of recurrent selection.
- This is useful for characters that can be measured on individual plants and having high heritability.
- This method is an extension of Mass selection.
- Desirable plants are selected on the basis of phenotype so it is also known as phenotypic recurrent selection.
- It does not include a tester.
- Plants were divided into two groups, a group to be discarded and a group to be propagated further on the basis of phenotypic scores taken from individual plants or their selfed progeny.
- First suggested by Jenkins in 1935.
- Heterozygous tester (Tester with broad genetic base i.e. open pollinated variety or a synthetic or segregating Generations) is used for testing the GCA for a character.
- RSGCA is used for improving those characters which are governed by additive genes.
- RSGCA is more effective with incomplete dominance and less effective with overdominance.
- RS-GCA May be used for increasing the frequency of desirable genes and improving the yielding ability of the population and the end product may be released as a synthetic variety or the population may be used for isolating superior inbreds.
- First proposed by Hull in 1945.
- Homozygous tester (Tester with narrow genetic base i.e. inbred) is used for testing the SCA for a specific Character
- The objective is the isolate from a population such lines that will combine well with a given inbred useful for selecting lines for SCA..
- RSSCA is more effective with overdominance & less effective with incomplete dominance.
- This method is used when a character is governed by non additive (Dominance and Epistasis) gene action.
- First proposed by Comstock, Robinson and Harvey in 1949.
- RRS would be useful. for selecting both for SCA and GCA and for improving two source population simultaniously.
- Two heterozygous testers are used as a tester. (Two heterozygous Populations A & B are used as a tester)
- This method is equally effective with incomplete, complete and overdominance.
- This method is used when a character is governed by both additive and non additive gene action.
- To improve heterozygous Population A - Heterozygous Population B is used as a tester strain.
- To improve heterozygous Population B- Heterozygous Population A is used as a tester strain.
References:
1. Allard, R.W. 2010. Principles of Plant Breeding. John Wiley and Sons, New York.
2. Phundan Singh, 2006. Essentials of Plant Breeding . Kalyani Publishers, New Delhi.
3. Singh, B.D. 2012. Plant Breeding: Principles and Methods. Kalyani Publishers, New Delhi.
About Author / Additional Info:
I am currently pursuing Ph.D. in Plant Breeding and Genetics from MPUAT-Udaipur (Raj.)