Recurrent selection sca1

The selection procedure of this method is same as for RSGCA, except that the tester is an inbred line which has narrow genetic base i.e tester

1. RECURRENT SELECTION FOR SPECIFIC COMBINING ABILITY Speaker: Vipin Kumar Pandey (Ph.D. Scholar) CLASS PRESENTATION (GP-603) Presentation Date: 11-1-2018

2. Recurrent Selection: The initial idea of recurrent selection was independently given by Hayes and Garber in 1919 and East and Jones in 1920 . But the term recurrent selection was first coined by Hull in 1945 . Definition: Recurrent selection is defined as reselection generation after generation , with intermating of selected plant to produce the population for the next cycle of selection . The idea of this method was to ensure the isolation of superior inbreds from the population subjected to recurrent selection. 

3.  The isolation of an outstanding inbred line depends on two factors : The proportion of superior genotypes present in the base population from which lines are isolated.   The effectiveness of selection during the inbreeding of desirable genes.

4. Types of Recurrent Selection: i ) Simple recurrent selection (SRS) ii) Recurrent selection for general combining ability (RSGCA)  iii) Recurrent selection for specific combining ability (RSSCA)  iv) Reciprocal recurrent selection ( RRS)

5. Simple Recurrent Selection (SRS) : A type of recurrent selection that does not include tester is referred as simple recurrent selection. It is also known as phenotypic recurrent selection.

6. Procedure of Simple Recurrent Selection:

7. Case study 1

8. Recurrent Selection for General Combining Ability (GCA ): A form of recurrent selection used to important the general combining ability of a population for a character and the heterozygous tester is referred as RSGCA. It is also known as half sib recurrent selection.  

9. Procedure of Recurrent Selection for General Combining Ability (RSGCA):

10. Recurrent Selection for SCA : It was originally proposed by Hull in 1945. Its a form of recurrent selection that is used to improve the SCA of a population for a character by using homozygous tester is referred as (RSSCA) recurrent selection for specific combining ability. It is also known as half site recurrent selection with homozygous tester.

11. Procedure: The selection procedure of this method is same as for RSGCA, except that the tester is an inbred line which has narrow genetic base i.e tester used must be an outstanding inbred. The differences in the performance of test cross are due to difference in their specific combining ability.

12. Recurrent Selection for SCA Cyclical selection of populations form families evaluate in trials recombine selections Pedigree selection and improvement of elite lines are also cyclical processes, but the population structure is not so clearly defined Selfing and introgression of new germplasm are common features of both selection systems Recurrent selection and development of lines can be integrated into a comprehensive system Bernardo, Chapt . 10

13. Selfing and Recurrent selection Selfing systems: Fixation of alleles is so rapid that the impact of selection is limited Probability of obtaining segregants with all of the favorable alleles controlling a quantitative trait is small Recurrent selection: systematically increases the frequency of favorable alleles maintains the genetic variation within a population to permit continual progress from selection Example: with 5 loci, all alleles have p =0.5 1/32 chance to get all of the good alleles Example: with 5 loci, all alleles have p =0.5  1/13 chance to get all of the good alleles

14. Case study 2

15. Reciprocal Recurrent Selection (RRS ): A form of recurrent selection used to improve both GCA and SCA of a population for a character using two heterozygous testers is known as RRS. It is also known as recurrent reciprocal half sib selection. Comstock et al. in 1949, proposed this method. Main Features of these Methods: 1) It is used for improvement of polygenic characters.  2) Selection is made on the basis of test cross performance.  3) Two heterozygous tester are used as a source of population.  4) It is used for improving population for GCA and SCA for specific characters.  5) It is equally effective with incomplete, complete and over dominance.  6) It is used for improvement of those characters, which are governed by both additive and non-additive gene action.  7) This method also requires three seasons for completion of each cycle of selection.

16. Procedure:

17. Merits: 1) Recurrent selection is an efficient breeding method for increasing the frequency of superior genes for various economic characters. 2) It helps in breaking repulsion phase of linkage.  3) It helps in maintaining high genetic variability due to repeated intermitting of heterozygous population . Demerits : 1) It is not directly used for the development of new varieties. 2) This method involves lot of selection crossing and selfing work.  3) It permits selfing , which leads to loss of genetic variability.

18. References Allard, R. W. 1960. Principles of plant breeding. John Wiley and Sons, inc , new York. Comstock, R. E., Robinson, H. F. and Harvey P. H. 1949. A breeding procedure designed to make maximum use of both general and specific combining ability. Agron . J . 41: 360-367. Singh, B.D. 2012 . Plant breeding principles and methods, Kalyani Publishers, New Delhi-110002. www.agriinfo.in/default.aspx?page=topic&superid=3&topicid=1773

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