Recurrent selection
- Hull (1952) defined recurrent selection as “Method which involves reselection generation after generation with interbreeding of selects to provide for genetic recombination”.
The advantages of recurrent selections are
- The rate of inbreeding can be kept at low level
- The frequency of favorable genes in the population will be increased and so.
- The chance of obtaining satisfactory individuals from the population will be increased because greater opportunity for recombination is present.
Types of recurrent selection
A) Simple Recurrent selection :
a) First year: Several phenotypically superior plants are selected selfed. Harvested separately and evaluated. Seed of superior plants retained and the rest are discarded.
b) Second year: Individual plant progeny rows are raised. The progeny rows are intercrossed in all possible combinations. Equal amounts of seed from each cross are taken and mixed. This forms the source for next selection cycle.
c) Third year: Seed obtained in II year is planted Number of superior plants selection and harvested separately. Seed evaluated. Seeds of superior plants retained and the rest discarded.
d) Fourth year: Progeny rows are raised. Inter crossed in all possible ways. Equal number of seed from each cross is composited. This mixed seed forms the source for next selection cycle.
B) Recurrent selection for general combining ability
a) First Year: Several phenotypically superior plants are selected from source population. Each selected plant is selfed as well as crossed to a tester with broad genetic base. The selfed seeds are harvested separately and saved for planting in the third year. The test crossed seeds also harvested separately.
b) Second year: A replicated yield trial is conducted using the test crossed seeds. At the end the superior progenies are identified.
c) Third year: Selfed seed (from the first year) of the plants that produced superior progenies on the basis of yield trial of second year is planted in separate progeny rows. These progenies are inter crossed in all possible combinations. Equal number of seed from each intercross is composited to raise the source population for next selection cycle.
d) IV year : Source population is raised from the composited seeds. Several phenotypically superior plants are selected. They are selfed and crossed to a tester (broad genetic base) selfed seed harvested separately and saved for planting in
e) V year : Test crossed seed also harvested separately.
f) Year : Repeat as in second year
g) VI year : Repeat as in third year. This completes the first selection cycle.
Advantages of Recurrent selection for general combining ability
- May be used for improving the yielding ability of the population and the end product may be released as a synthetic variety or
- May be used for increasing the frequency of desirable genes in the population and the population may be used for isolating superior inbreeds.
C) Recurrent selection for specific combining ability :
- The objective is to isolate from a population such lines that will combine well with a given inbred useful for selecting lines for SCA.
- The procedure for recurrent selection for SCA is identical with that of recurrent selection for GCA, expect that the tester used here is an inbred (narrow genetic base)
D) Reciprocal recurrent selection:
- For selecting both for SCA and GCA
- For improving two source population simultaneously.