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Bulk method pedigree method &line breeding
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Transcript of Bulk method pedigree method &line breeding
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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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