breeding self pollinated crops

1

Prepared byPawan Kumar NagarM.Sc. (Fruit science)

Breeding Breeding Self Pollinated CropsSelf Pollinated Crops

General methods: Special methods:1.Plant introduction 1. Mutation breeding2. Pureline selection 2. Polyploidy breeding3. Mass selection 3. Transgenic breeding4. Pedigree method 4. Molecular breeding5. Bulk method6. Single Seed descent method7. Back cross method8. Hetrosis breeding

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.

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.

Pure line selection Pure line selection

Johannsen (1903,1926), a Danish biologist, developed the concept of pureline theory working with Princess variety of common bean(Phaseolus vulgaris).

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

ApplicationsPure-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.

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.

Disadvantages1.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.

Mass selectionMass selection

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.

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.

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.

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.

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.

Cultivar development procedure

Purification of an existing cultivar

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.

Advantages1.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.

Disadvantages1.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

MASS SELECTION VS PURE LINE MASS SELECTION VS PURE LINE SELECTIONSELECTION

Line mixtureLine mixture

Bulk of Bulk of phenotypicallphenotypicall

yysimilar plantssimilar plants

Cultivar registerCultivar registerand marketingand marketing

Single plant offspringsSingle plant offsprings

L1 L2 L3……. L1 L2 L3……. LNLN

Register and Register and marketmarketthe best pure the best pure lineslines

Mass selectionMass selection Pure line selectionPure line selection

Heterogenous cultivarsHeterogenous cultivars Homogenous cultivarsHomogenous cultivars






L1 L2 L3……. L1 L2 L3……. LNLN









L1 L2 L3……. L1 L2 L3……. LNLN




MULTILINE BREEDING

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).

1. Mixtures of isolines.

2. Mixture of closely related lines.

3. Mixture of unrelated or distinctly different genotypes.

1. It has genetic diversity.

2. It should have normal resistance.

3. Components should be uniform agrnomically.

4. It should have yield advantage.

1. Selection of recurrent parent.2. Selection of donor parents.3. Transfer of resistance.4. Mixing of isolines.

1. Identical to recurrent parent2. Loss to cultivator is low.3. Spreading of diseases is slow4. It reduces the risk of homogenising the

pathogen population globally.5. Stabilises and optimizes production on

farm.

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.

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.

breeding self pollinated crops

Education