recurrent selection

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recurrent selection

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Assisgnment Presentation on “Recurrent selection” Seminar Incharge : Dr. J.B.Patel Assistant. Res. Sci. SDAU sardarkrusinagar ` Presented by: Patil Ramanand .V Reg. No. 04-00721-10 M.Sc.(GPB.)

Introduction:

Introduction Recurrent selection :- “Reselection generation after generation with interbreeding of selected plants to provide for genetic recombination.” The initial idea about recurrent selection was independently given by Hayes and Garber in 1919, and East and Jones in 1920. The Procedure of recurrent selection was described by Jenkins in 1940. The term recurrent selection was coined by Hull in 1945.

Recurrent selection:

Recurrent selection Main features of recurrent selection:- 1) Application:- it is used in cross pollinated species. & now it is also used in self pollinated species. 2) Base population:- a) open pollinated variety b) a synthetic variety c) progeny of intercrosses among selected inbreeds d)a double cross e) a single cross. 3) Important steps:- simple recurrent selection are 5 main steps. 1) selection of superior plants from base population 2) selfing of selected plants 3) growing progeny of selected plants in the next season from selfed seed, 4) intermating among progeny 5) bulking of crossed seed in equal quantity. The bulk seed is used for next cycle of selection. 4) use of end product:- a) producing homozygous inbreds by selfing b) the production of hybrid varieties c) the production of synthetic varieties. 5) Impact :- Recurrent selection is used to improve the frequency of desirable alleles for a character in a population.

Types of recurrent selection:

Types of recurrent selection 1.) Simple recurrent selection 2.) Recurrent selection for general combining ability. 3.) Recurrent selection for specific combining ability 4.) reciprocal recurrent selection.

Comparison :

Comparison Particulars Recurrent selection for gca Recurrent selection sca application Used to improve polygenic traits Also used to improve polygenic traits. Basis of selection Test cross performance Test cross performance Tester used Heterozygous Homozygous effectiveness Incomplete dominance Complete and overdominance Condition of use Used when additive gene action is important Non additive gene action gene action is important impact Improve gca characters Improve sca characters

Simple recurrent selection:

Simple recurrent selection a type of recurrent selection that does not include a tester also called phenotypic recurrent selection. The tester is not used in this scheme it does not measure the combining ability The selection is based on phenotype or simple test. This method is useful only for those characters which have high heritability.

Simple recurrent selection:

Simple recurrent selection First year- superior plants are selected from heterozygous base population. Second year- These plants are grown from the selfed seed Make all possible crosses among progeny Harvest crossed seeds and bulked them. Complete the original cycle of selection. Third year- grow crop from bulk seed of crosses. Again self pollinated a number of plants. Select superior plants at maturity. Fourth year- progeny of selected plants are grown from selfed seed and intermating is done like first year. The crossed seed is composited in equal quanity for use in the next cycle of selection.

Recurrent selection for GCA:

Recurrent selection for GCA A form of recurrent selection which is used to improve general combining ability of a population for a character using heterozygous tester. This method is used for genetic improvement of quantitative characters. Selection on test cross performance This method used for improving GCA of population for a character. Improvement of those characters which governed by additive gene action.

Recurrent selection for GCA:

Recurrent selection for GCA First year- superior plants for the character under improvement are selected from the base population. The selected plants are selfed and also crossed to a heterozygous tester having broad genetic base. Second year- the crossed seed are sown and combining ability of the selected plants is evaluated and plants with good gca are identified. Third year- the progeny of selected plants with good gca are grown from their selfed seed kept in cold store. These progeny are intermated in all possible combinations and their crossed seed is composited to from a new source population for further selection. This complete original selection cycle. In the same way another cycle can be completed in three years 4 th to 6 th year.

Recurrent selection for SCA:

Recurrent selection for SCA A form of recurrent selection that is used to improve the specific combining ability of a population for a character using homozygous tester also called half sib recurrent selection with homozygous tester. Genetic improvement of polygenic characters. Selection is made on the basis of test cross performance

Reciprocal Recurrent Selection:

Reciprocal Recurrent Selection A form of recurrent selection that is used to improve both gca and sca of a population for a character using two heterozygous testers is known as reciprocal recurrent selection. It is also termed as recurrent reciprocal half sib selection. This scheme was proposed by Comstock, et al . in 1949. Improvement of polygenic characters. Selection is made on the basic of test cross performance.

Reciprocal Recurrent Selection:

Reciprocal Recurrent Selection First year- several phenotypically superior plants are selected from population A and B. Cross several plants of group A with group B and vice versa. Self pollinated selected plants in both groups. Second year- evaluated performance of crosses made in A and B groups. Identify superior crosses in A and B populations. Third year- grow crop from selfed seed of first year of superior crosses in A and B group. Make all possible crosses within A and B group. Composite of seeds from intercrosses. Fourth year- the A and B population are grown from the composite crossed seeds of respective population obtained in third year. Then operation of first year are repeated. Fifth year- The operation of second year are repeated. Sixth year- The operation of third year are repeated.

Merits:

Merits 1) Recurrent selection is an efficient breeding method for increasing the frequency of superior genes in a population for economic characters. 2) this method also help in maintaining high genetic variability in a population due to repeated intermating of heterozygous plant. 3) The selection is made on the basis of test cross performance and only selected plants are allowed for intermating .

Demerits :

Demerits 1.) this method is not used directly for the development of new varieties. The new varieties are developed by the use of end product in hybridization. This is only method of population improvement. 2.) This method involves lot of selection, crossing and selfing work. 3.) This method permits selfing which leads to loss of genetic variability. Recurrent selection has been used for the improvement of oil content in maize, fiber strength in cotton and sugar content in sugar beet and sugarcane.

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