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Presented by:

Pawan Kumar Nagar

M.Sc. (POMOLOGY)

Different types of Selection and their

Uses

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Selection“ Identification and isolation of plants having the desirable combination of characters, and growing

their progeny only”History:• 1843: Le Couteur published his results on selection in wheat• About the same time Patrick Shireff practiced individual plant

selection in wheat and oats• 1857: Hallet practised single plant selection in wheat, oats and

barley• Vilmorin proposed Individual plant selection based on progeny

testing• 1903: Johannsen proposed pureline theory

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Pureline selection• In Pureline selection a large number of plants are selected

from a self pollinated crop and harvested individually; individual plant progenies from them are evaluated, and the best progeny is released as a pureline variety

Improvement of local varieties

Selection in introduced varieties

Improvement of old pureline varieties

Selection for a new characteristic in a pureline

APPLICATIONS

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Mass selection• In Mass selection a large number of plants of similar

phenotype are selected and their seeds are mixed together to constitute the new variety

• Breeder aims at increasing the frequency of desirable alleles in the population

Improvement of local varieties

Purification of existing pureline varieties

APPLICATIONS

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Selection schemes with progeny test

• Simplest form is Ear-to-row method• Developed by Hopkins in 1908

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Modification of progeny selection

1. Simple recurrent selection2. Recurrent selections for SCA 3. Recurrent selections for GCA 4. Reciprocal recurrent selection

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Recurrent selection• The initial idea of recurrent selection was independently given by

Hayes and Garber in 1919 and East and Jones in 1920• The term recurrent selection was first coined by Hull in 1945• Definition: 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

• The isolation of an outstanding inbred line depends on two factors:

1) The proportion of superior genotypes present in the base population from which lines are isolated and 2) The effectiveness of selection during the inbreeding of desirable genes

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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”

Procedure:1) A number of plants with desirable phenotype are selected and self-

pollinated in the 1st year2) In the second year, separate progeny rows are grown from selfed seeds

of the selected plants 3) The progenies are inter crossed in all possible combination by hand4) Equal amount of seed from each cross is composited to produce the next

generation This complete the original selection cycle

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contd..

5) In the third year, bulked seeds are grown and superior plants are selected and selfed, like first year

6) In the fourth year, progeny of selected plants are grown from selfed seed and intermating is done like first year

7) The crossed seed is composited in equal quantity for use in the next cycle of selection. This complete first cycle of simple recurrent selection

Thus selection cycles may be repeated till the desired improvement is achieved

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Recurrent Selection for General Combining Ability

A form of recurrent selection used to improve 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 • Developed by Jenkins in 1940• The progeny for progeny testing are obtained by crossing thee selected

plants to a tester strain with a broad genetic base• A tester strain is the common parent mated to a number of lines, strains

or plants• A tester with a broad genetic variability is used : e.g.: an open pollinated

variety, a synthetic variety or segregating generations of crosses

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Procedure:

1) First Year: • Phenotypically superior plants are selected from the base

population. The selected plants are selfed and also crossed to a number of randomly selected plants from a tester having broad genetic base. The selfed seeds are harvested seperately

2) Second Year: • A replicated yield trial is conducted using the plant x tester

seeds, and plants producing superior test cross progenies are identified

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Contd..3) Third Year: • The progeny of selected plants with good GCA are grown from

their selfed seed in rows. These progenies are inter mated in all possible combinations and their crossed seed is composited to form a new source of population for further selection. This complete original selection cycle

• In the same way another cycle can be complete in sixth year called as first recurrent selection cycle. Many such cycles may be made to obtain desired results

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USES

This method is effective in changing GCA in the direction of selection

Effective in increasing the yielding ability of the population

The population will be identical with synthetic variety This method is also used for the isolation of inbreds

with superior GCA

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Recurrent Selection for SCA 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 recurrent selection for specific combining ability (RSSCA)

• It was originally proposed by Hull in 1945• Procedure: The selection procedure of this method is same as for RSGCA,

except that the tester is an inbred line .The differences in the performance of test cross are due to difference in their specific combining ability

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1) First Year: • Several plants are selected and selfed. The selected plant (male) are also

crossed to a tester 2) Second Year:

• R.Y.T is conducted using test cross progeny and outstanding progenies are identified

3) Third Year: • Selfed seed from the plants are planted in separate progeny row in a crossing

block. All possible inter crosses are made by hand. Equal amount of seed is composited, this complete the original selection cycle

4) Fourth Year: • The composited intercross seed is planted and operations of 1st year are

repeated. 5) Fifth Year:

• Second year operations are repeated6) Sixth Year:

• Third year operations are repeated. • This completes the first recurrent selection cycle.

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Reciprocal Recurrent Selection (RRS)

A form of recurrent selection used to improve two different populations in their ability to combine well with each other is known as RRS

• Comstock, Robinson and Harvey in 1949, proposed this method

• A random sample of plants from population A serves as the tester for plants selected from population B

• Similarly a random sample of plants from population B serves as the tester for plants selected from population A

• It would select for both GCA and SCA

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Main Features of these MethodsIt is used for

improvement of polygenic characters

Selection is made on the basis of test

cross performance

Two heterozygous tester are used as a

source of population

It is used for improving

population for GCA and SCA for specific

characters

It is equally effective with incomplete,

complete and over dominance

It is used for improvement of those characters,

which are governed by both additive and

non-additive gene action

This method also requires three

seasons for completion of each cycle of selection

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Procedure1) First Year: • Several phenotypically superior plants are selected from population ‘A’

and ‘B’. The pollen of some selected plants of ‘A’ population is used to cross large number of randomly selected plants of population ‘B’. Similarly pollen of some selected plants of ‘B’ population is used to cross- large number of plants of population ‘A’. All the plants of population A and B used as pollen parents in the crosses are selfed.

2) Second Year: • Test crosses seeds are grown in RYT. The superior progeny are identified. 3) Third Year: • The selfed seeds of those A and B plants whose progeny were found

superior in replicated trials are grown in separate rows in crossing block. All possible crosses are made. The crossed seeds are composited in equal quantity to raise A1 generation. Similarly, crossed seeds of ‘B’ block are bulked to raise B1 generation. This completes original cycles of selection

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Contd..4) Fourth Year: • The A1 and B1 population are grown from the composite

crossed seeds of respective population obtained in third year. The operations of first year are repeated

5) Fifth Year: • Operation of second year are repeated6) Sixth Year: • Operation of third year are repeated• This completed first cycle of reciprocal recurrent selection Such cycles may be continued till the desired improvement is

achieved

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Comparison Particular Recurrent selection for

GCARecurrent selection for

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 over dominance

Condition of use Used when additive gene action is important

Non additive gene action is imporatant

Impact Improve GCA characters Improve SCA characters

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Merits

• Most suited for characters with high heritability• It increases the frequency of desirable genes and genotypes in

the selected population• Little or no reduction in variability• Relatively low inbreeding

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Demerits

1) It is not directly used for the development of new varieties2) This method involves lot of selection, crossing and selfing

work3) It permits selfing, which leads to loss of genetic variability

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REFERENCE• Plant breeding; Principles and method, B.D.Singh,

Kalyani publishers• An introduction to plant breeding, Jack Brown and Peter

Caligari, Blackwell publishers

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