Self incompatibility

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MODES OF REPRODUCTION PRESENTED BY: Pawan Nagar Reg. no.: 04-2690-2015 M.Sc.(Fruit Science)

Transcript of Self incompatibility

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MODES OF REPRODUCTION

PRESENTED BY: Pawan NagarReg. no.: 04-2690-2015M.Sc.(Fruit Science)

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Self incompatability was first reported by Koelreuter.

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Self-incompatibility (SI) It refers to the inability of a plant with

functional pollen to set seeds when self pollinated. It is the failure of pollen from a flower to fertilize the same flower or other flowers of the same plant.

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Self-incompatibility (SI) is a general name for several genetic mechanisms in angiosperms, which prevent self-fertilization and thus encourage out-crossing and allogamy.

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REASONS FOR SELF-INCOMPATABILITY

1) Pollen stigma interaction.2) Pollentube and style interaction.

3) Pollentube and ovary interaction.

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General features of Self-incompatibilityPrevent selfing and promotes out-breeding so

increases the probability of new gene combinations. Causes may be morphological, physiological,

genetical or biochemical. Normal seed set on cross pollination. May operate at any stage between pollination and

fertilization. Reduces homozygosity.

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Criteria Types

Flower morphology

Heteromorphic self incompatibility

Distyly

Tristyly

Homomorphic self incompatibility

Sporophytic self incompatibility

Gametophytic self incompatibility

Classification of Self-incompatibility

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Heteromorphic self-incompatibilityThe genes responsible for self-

incompatibility in heterostylous flowers are strongly linked to the genes responsible for flower polymorphism, so these traits are inherited together.

The associated concepts are distyly and tristyly.

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What is Distyly ? Here, both stamens and styles are of two types. Stamens may be low and high. styles short and long. It is determined by a single gene, with two

alleles. The flower with short style and high stamen is

called as thrum type and flower with long style and low stamen is called as pin type. Both thrum and pin flowers differ for six characters in addition to stamen and style length.

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Stigma

Cross ResultSs (thrum) X Ss (thrum) Incompatible

ss (pin) X ss (pin) IncompatibleSs(thrum) X ss (pin) 1:1ss (pin) X Ss(thrum) 1:1

Distyly

Thrum Pin

Anther

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What is Tristyly?In tristyly, styles and stamens have three different

positions.

It is determined by two genes S and M, each with two alleles.

S gives rise to short style, S and M to medium style and s and m to long style. The number of possible genotypes is greater, but a

1:1 ratio exists between individuals of each SI type.

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Short Style Medium Style Long Style

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HOMOMORPHIC SELF- INCOMPATABILITY

1) GAMETOPHYTIC SELF- INCOMPATIBILITY.2) SPOROPHYTIC SELF INCOMPATIBILITY.

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1) GAMETOPHYTIC SELF- INCOMPATIBILITY This type self- incompatability was

first described by East and Mangeldorf in 1925 in tobacco.

In this system, the incompatibility reaction of pollen is determined by its own genotype and not by the genotype of the plant on which it is produced.

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The rules: The S loci are

extremely polymorphic; that is, there is an abundance of multiple alleles in the population.

Incompatibility is controlled by the single S allele in the haploid pollen grain.

Thus a pollen grain will grow in any pistil that does not contain the same.

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Cross CompatibilityS1S2 X S1S2 Fully incompatibleS1S2 X S1S3 Partially compatibleS1S2 X S3S4 Fully compatible

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2)SPOROPHYTIC SELF INCOMPATIBILITY This type of self incompatability

was first reported by Hughes anb Babcock in 1950 in Crepis foetida.

In this system incompatibility reaction of pollen is governed by genotype of plant on which pollen is produced,and not by genotype of pollen.

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The rules:

• Pollen will not germinate on the stigma (diploid) of a flower that contains either of the two alleles in the sporophyte parent that produced the pollen.

• This holds true even though each pollen grain being haploid contains only one of the alleles.

• For example, the S2 pollen, which was produced by a S1S2 parent, cannot germinate on an S1S3 stigma.

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TEMPORARY SUPPRESION OF SELF INCOMPATABILITY1) Bud pollination: Pollination of immature bud

with mature pollen.2) Delay pollination:Pollination of aged pistil

several day after maturity with normal incompatible pollen.

3) Late season pollination: Self pollination at end of flowering season also lead to seed set.

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4) Irradiation of style: In solanaceae, acute irradiation with X-rays or Gamma rays induces a temporary loss of self incompatibility.

5) High temperature: Treatment of high temperature ranging from 30-600 C lead to break down of self incompatibility in lycopersicon, brassica spp.

6) Double pollination: In some spp. S.I. mating become possible when incompatible pollen is applied as a mixture with a compatible pollen or it applied after pollination with a compatible pollen.

7) Surgical method: In this method pollen is applied in direct contact with ovule result in break down of S.I.

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ELIMINATION OF SELF INCOMPATABILITY

1) In the case of single locus gametophytic system,incompatibility may be eliminated by doubling the chromosome number.

2) Isolation of self-fertile (Sf) mutations is a very useful tool in the elimination of self incompatibility.

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 Importance of Self-Incompatibility In Plant Breeding

Self-incompatibility effectively prevents self-pollination; as a result, it has a profound effect on plant breeding approaches and objectives.

(1)  In self incompatible fruit trees, it is necessary to plant two cross-compatible varieties to ensure fruitfulness.

 (2) Self-incompatibility may be used in hybrid seed

production. For that, two self-incompatible but cross-compatible lines are to be interpolated; seeds obtained from both the lines would be hybrid seed.

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(3) Self incompatibility provides a way for hybrid seed production without emasculation and without resorting to genetic or cytoplasmic male sterility.

(4) Self incompatibility system permits combining of desirable genes in a single genotype from two or more different sources through natural cross pollination which is not possible in self compatible species .

(5) In case of pineapple, commercial clones are self-incompatible. As a result, their fruits develop parthenocarpically & are seedless.

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6)There is no roughing problem in self incompatible line.

7) Labour cost is less and seed production is more in self incompatible mechanism.

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1. It is very difficult to produce homozygous inbred lines in a self incompatible species.

2. Bud pollination has to be made to maintain the parental lines.

3. Self incompatibility is affected by environmental factors such as temperature and humidity. Incompatibility is reduced or broken down at high temperature and humidity.

4. There is a limited use of self-incompatibility due to problems associated with the maintenance of inbred lines through hand pollination as it is tedious and costly.

Limitations

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