This document provides information on breeding methods for self-pollinated crops. It discusses pureline selection, mass selection, and multiline breeding. Pureline selection involves isolating homogenous lines from a mixed population and selecting the best ones. Mass selection selects desirable plants directly from a mixed population based on phenotype. Multiline breeding develops mixtures of isolines or related lines that differ in specific genes to provide disease resistance while maintaining uniform agronomic traits.
The mating or crossing of two plants or lines of dissimilar genotype is known as hybridization. The chief objective of hybridization is to create genetic variation, when two genotypically different plants are brought together in F1. Here, we are going to discuss about different strategies and tools used for hybridization.
Hybridization between individuals from different species belonging to the same genus or two different genera, is termed as distant hybridization or wide hybridization, and such crosses are known as distant crosses or wide crosses.
The mating or crossing of two plants or lines of dissimilar genotype is known as hybridization. The chief objective of hybridization is to create genetic variation, when two genotypically different plants are brought together in F1. Here, we are going to discuss about different strategies and tools used for hybridization.
Hybridization between individuals from different species belonging to the same genus or two different genera, is termed as distant hybridization or wide hybridization, and such crosses are known as distant crosses or wide crosses.
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SELECTION METHODS IN SELF-POLLINATED CROPS viz., mass selection, pureline sel...AMIT RANA Ph. D Scholar
MASS SELECTION
Mass selection is a method of breeding in which individual plants are selected on the basis of phenotype from a mixed population , their seeds are bulked and used to grow the next generation.
Selection cycle may be repeated one or more times to increase the frequency of favorable alleles - phenotypic recurrent selection.
PURELINE SELECTION
A pureline is the progeny of a single homozygous plant of a self-pollinated species. All the plants in a pureline have the same genotype and the phenotypic variation within a pureline is due to the environment alone and has no genetic basis. However, variation within a pureline is not heritable. Hence selection in a pureline is not effective. Johannsen (1903,1926), a Danish biologist, developed the concept of pureline theory working with Princess variety of French bean (Phaseolus vulgaris), which showed variation for seed size. From a commercial seed lot he selected seeds of different sizes and grew them separately. The progenies differed in seed size. Progenies from larger seeds produced larger seeds than those obtained from smaller seeds. This clearly showed that the variation in seed size in the commercial seed lot of princess variety had a genetic base. As a result selection for seed size was effective.
Introduction
PEDIGREE SELECTION
Pedigree selection is a widely used method of breeding self-pollinated species.
A key difference between pedigree selection and mass selection or pure-line selection is that hybridization is used to generate variability (for the base population), unlike the other methods in which production of genetic variation is not a feature.
The method was first described by H. H. Lowe in 1927.
Pedigree selection is a breeding method in which the breeder keeps records of the ancestry of the cultivar.
The base population is established by crossing selected parents, followed by handling an actively segregating population.
Documentation of the pedigree enables breeders to trace parent–progeny back to an individual F2 plant from any subsequent generation.
The breeder should develop an effective, easy to maintain system of record keeping.
Pedigree selection is applicable to breeding species that allow individual plants to be observed, described, and harvested separately.
In this presentation you will come to know about the HANDLING OF SEGREGATING GENERATIONS, that is (PEDIGREE METHOD, MASS PEDIGREE METHOD, BULK METHOD, SINGLE SEED DESCENT METHOD).
Clone is the progeny of a single plant, produced by asexual reproduction
Clonal selection is the selection of the most desirable members of a clone for continued vegetative propagation rather than for sexual reproduction.
The members of a clone keep up genetic constancy.
So by clonal selection and continued vegetative propagation, the desirable qualities of plants can be maintained for long.
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2. General methods: Special methods:
1.Plant introduction 1. Mutation breeding
2. Pureline selection 2. Polyploidy breeding
3. Mass selection 3. Transgenic breeding
4. Pedigree method 4. Molecular breeding
5. Bulk method
6. Single Seed descent method
7. Back cross method
8. Hetrosis breeding
3. Symbols for basic crosses
F: The symbol F (for filial) denotes the progeny of a
cross between two parents.
: The symbol is the notation for selfing.
S: The S notation is also used with numeric subscripts.
In one usage S0
= F1
; another system indicates S0
= F2
.
4. Pureline refers to the homogenous progeny of a
self pollinated homozygous plant.
Mass selection is a method of breeding in which
individual plants are selected on the basis of
phenotype from a mixed population , their seeds
are bulked and used to grow the next generation.
The deliberate mixture of isolines, closely related
lines or unrelated lines are referred to as
multilines, and the method of developing a
variety from any of these mixtures is known as
multiline breeding.
6. Johannsen (1903,1926), a Danish biologist,
developed the concept of pureline theory
working with Princess variety of common
bean(Phaseolus vulgaris).
7. Key features:
1. Homogeneous
2. Nonheritable variation
3. Highly uniform
4. Selection is ineffective
5. Narrow adaptation
6. More prone to new diseases
7. Isolation of pure lines
8. Sources of variation
8. Applications
Pure-line breeding is desirable for developing cultivars for certain
uses:
1.Varieties for mechanized production that must meet a certain
specification for uniform operation by farm machines.
2.for a discriminating market for visual appeal (e.g., uniform
shape, size).
3.for the processing market (e.g., demand for certain canning
qualities).
4.Advancing that appear in a population (e.g., a mutant flower for
ornamental use).
5.Improving newly domesticated crops that have some variability.
9.
10. Advantages:
1.It is a rapid breeding method.
2.The method is inexpensive to conduct.
3.The variety developed by this method has great “eye
appeal” because of the high uniformity.
4.It is applicable to improving traits of low heritability,
because selection is based on progeny performance.
5.Only the best pure line is selected for maximum
genetic advance.
11. Disadvantages
1.The purity of the variety may be altered through
admixture, natural crossing with other varieties and
mutations.
2.Narrow genetic base and so poor adaptability.
3.A new genotype is not created.
4.The method promotes genetic erosion
5.Progeny rows take up more resources (time, space).
6.Only applicable to self pollinated species.
13. As an ancient art, farmers saved seed from
desirable plants for planting the next season’s
crop, a practice that is still common in the
agriculture of many developing countries.
Mass selection is often described as the oldest
method of breeding self-pollinated plant
species.
This method of selection is applicable to both
self- and cross-pollinated species. But it is more
used for cross-pollinated crops.
14. Key features
The purpose of mass selection is population improvement
through increasing the gene frequencies of desirable genes.
Selection is based on plant phenotype.
Mass selection is imposed once or multiple times (recurrent mass
selection).
The improvement is limited to the genetic variability that existed
in the original populations.
The goal in mass selection is to improve the average
performance of the base population.
15. 1. Positive mass selection:
Desirable plants are selected from a mixed
population.
Base material is old varieties or land races.
2. Negative mass selection:
Undesirable off type plants are removed from a
mixed population.
used for varietal purification in seed production
and certification programs.
16. The success of mass selection mainly
depends on three factors:
1.Variability in the base population.
2. Mode of inheritance of the character to be
improved.
3. Heritability of the character.
17. There are two defects of mass selection:
1. No control on pollination.
2. Selection is based on phenotype.
Modifications are;
1. Rejection of inferior plants.
2. Use of composite pollen.
3. Stratification of field.
20. Applications
1.to maintain the purity of an existing variety that has become
contaminated.
2.to develop a variety from a base population created by
hybridization.
3.to preserve the identity of an established variety or soon-to-be-
released new variety.
4.Some breeders use mass selection as part of their breeding
program to rogue out undesirable plants, thereby reducing the
materials advanced and saving time and reducing costs of
breeding.
21. Advantages
1.It is rapid, simple, and straightforward.
2.It is inexpensive to conduct.
3.The variety is phenotypically fairly uniform even though it is
a mixture of pure lines.
Disadvantages
1.The traits of interest should have high heritability.
2.Less phenotypic uniformity than other procedures.
3.With dominance, heterozygotes are indistinguishable from
homozygous dominant genotypes.
22. 22
MASS SELECTION VS PURE LINEMASS SELECTION VS PURE LINE
SELECTIONSELECTION
Line mixtureLine mixture
Bulk ofBulk of
phenotypicallyphenotypically
similar plantssimilar plants
Cultivar registerCultivar register
and marketingand marketing
Single plant offspringsSingle plant offsprings
L1 L2 L3……. LNL1 L2 L3……. LN
Register and marketRegister and market
the best pure linesthe best pure lines
Mass selectionMass selection Pure line selectionPure line selection
Heterogenous cultivarsHeterogenous cultivars Homogenous cultivarsHomogenous cultivars
Line mixtureLine mixture
Bulk ofBulk of
phenotypicallyphenotypically
similar plantssimilar plants
Cultivar registerCultivar register
and marketingand marketing
Single plant offspringsSingle plant offsprings
L1 L2 L3……. LNL1 L2 L3……. LN
Register and marketRegister and market
the best pure linesthe best pure lines
Mass selectionMass selection Pure line selectionPure line selection
Heterogenous cultivarsHeterogenous cultivars Homogenous cultivarsHomogenous cultivars
Line mixtureLine mixture
Bulk ofBulk of
phenotypicallyphenotypically
similar plantssimilar plants
Cultivar registerCultivar register
and marketingand marketing
Single plant offspringsSingle plant offsprings
L1 L2 L3……. LNL1 L2 L3……. LN
Register and marketRegister and market
the best pure linesthe best pure lines
Mass selectionMass selection Pure line selectionPure line selection
Heterogenous cultivarsHeterogenous cultivars Homogenous cultivarsHomogenous cultivars
24. Multilines:
First Suggested IN OATS BY JENSEN IN 1952
Multilines are developed for self-pollinating species.
These cultivars consist of a mixture of specially developed
genotypes called isolines (or near isogenic lines) because they differ
only in a single gene (or a defined set of genes).
Isolines are developed primarily for disease control, even though
these cultivars could, potentially, be developed to address other
environmental stresses.
Isolines are developed by using the techniques of backcrossing in
which the F1 is repeatedly crossed to one of the parents (recurrent
parent) that lacked the gene of interest (e.g., disease resistance).
25. 1. Mixtures of isolines.
2. Mixture of closely related lines.
3. Mixture of unrelated or distinctly
different genotypes.
26. 1. It has genetic diversity.
2. It should have normal resistance.
3. Components should be uniform
agrnomically.
4. It should have yield advantage.
27. 1. Selection of recurrent parent.
2. Selection of donor parents.
3. Transfer of resistance.
4. Mixing of isolines.
28. 1. Identical to recurrent parent
2. Loss to cultivator is low.
3. Spreading of diseases is slow
4. It reduces the risk of homogenising the
pathogen population globally.
5. Stabilises and optimizes production on
farm.
29. 1. Seed is to be repaced every few years.
2. Production and mainatenance is time taking
job.
3. It has to be regularly reconstituted, and new
lines have to be continuously developed.
4. Seed certification poses difficulties.
5. It is less attractive, less uniform and costly
method.
30. Multiline cultivars have been developed for
commercial cultivation in oats, wheat,
soybean and peanut in USA.
In India three multiline varieties, viz.
KSML 3, MLKS 11 and KML 7404 have
been released in wheat from Punjab.