self incompatibility

TOPIC

SELF-INCOMPATIBILITYSELF-INCOMPATIBILITY

Prepared by:Prepared by:

Ezaz AslamEzaz Aslam : : 92 Zia Ur Rahman : Zia Ur Rahman : 438438

Hammad UddinHammad Uddin :: 51 Adnan AhmadAdnan Ahmad : : 462462 Course:Course: Morphology & Reproductive System of Crop PlantsMorphology & Reproductive System of Crop Plants

B.Sc (Hons) – 3B.Sc (Hons) – 3rdrd Year , 5 Year , 5thth semester semester

Teacher:Teacher: Dr. Sultan AkbarDr. Sultan Akbar

Department:Department: Plant Breeding & GeneticsPlant Breeding & Genetics University of Agriculture, PeshawarUniversity of Agriculture, Peshawar

Contents: Introduction Types of Self-Incompatibility Importance of SI in Plant Breeding Limitations References

INTRODUCTION 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 Self-incompatibility is a general name for several

genetic mechanisms in angiosperms, which prevent self-fertilization and thus encourage cross pollination or allogamy (Cross-Fertilization)

Cause: In plant with SI, when a pollen grain

produced in a plant reaches a stigma of the same plant or another plant with similar genotype, the process of pollen germination, pollen tube growth, ovule fertilization, and embryo development is halted at one of its stages and no seeds are produced.

SI is one of the most important mean to prevent selfing and promote variations by crossing

General Features of Self Incompatibility Prevent selfing and promotes out-breeding so

increasing the probability of new gene combinations

Its cause may be morphological, physiological, genetical or boichemical

Normal seed set on cross-pollination Reduce Homozygosity In plats, Self-incompability is often inherited

by a single gene “S” “S” with different alleles (e.g S1, S2,S3, etc.) in the specie population

Types of Self-incompatibility1.1. Homomorphic Self-incompatibility:Homomorphic Self-incompatibility:

a. Gametophytic Self-incompatibility (GSI) b. Sporophytic Self-incompatibility (SSI)

2.2. Heteromorphic Self-incomatibility:Heteromorphic Self-incomatibility: a. Distyly b. Tristyly

3.3. Late-acting Self-incomaptibility (LSI)Late-acting Self-incomaptibility (LSI)

Homomorphic Self-incompatibility and its types

Def: “Type of self-incompatibility in which the flowers have similar

morphology.” It results due to physiological causes rather than difference

in flower morphology They are controlled by s single gene (S) having multiple

alleles

It has 2 types:

1.1. Gametophytic Self-incompatibility:Gametophytic Self-incompatibility: When the self-incompatibility is controlled by the genetic

constitution of pollen grain GSI was first described by EastEast and MangelsdorMangelsdor in 19251925 in

Nicotiana sanderae

Here the pollen grains are unable to germinate on stigma with similar alleles as that of pollen.

Cont… In a single system there are three types of matings. Crosses Compatibility

S1S2 x S3S4 = Fully Compatible S1S2 x S1S3 = Partially Compatible S1S2 x S1S2 = Fully Incompatible

Examples: potatoes, wild tomatoes, tobacco, roses, bajara, rye, sugar beet

Cont…2. 2. Saprophytic Self-incompatibility:Saprophytic Self-incompatibility:

First introduced by HughesHughes and BabcockBabcock in 1950 in Crepis Crepis foetidafoetida

Type of Self-incompatibility which is controlled by the genotype of pollen producing plant

Progeny from cross between two genotypes is either fully fertile or complete sterile

It is also controlled by single gene (S) with multiple alleles (Imp!)(Imp!) Pollen does not germinate on the stigma of a flower

that contains either of the two alleles that are present in the sporophyte parent which produced the pollen.

The same condition is applicable even though each pollen grain (haploid) contains only one of the alleles

Cont…

For example, S1 or S2 pollen, which was produced by S1S2 parent, cannot germinate on a S1S3 or S1S2 stigma and will germinate only on S3S4

Order of dominance followed is S1 >S2> S3> S4

Heteromorphic Self-incompatibility Type of SI which is due to difference in the morphological features

of the flower It consists of:1.1. Distyly:Distyly: Here both stamens and pistils are of two types:a.a. Pin type :Pin type : Flower with long style and short stamenb.b. Thrum type:Thrum type: Flower with short style and high stamen

It is determined by a single gene, with 2 alleles

Cross Result

(ss)Pin x (ss) Pin Self-incompatible (Ss)Thrum x (Ss) Thrum Self-incompatible (ss)Pin x (Ss)Thrum Compatible

Cont… Primula is the best example of Distyly

22. Tristyly:. Tristyly: Style and stamens have three different sizes (small,

medium, large) It is determined by 2 genes S and M, each with 2 alleles1. S gives rise to short style2. S and M to Medium style &3. 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.

Late-Acting Self-incompatibility It is also known as Ovarian Self-Ovarian Self-

incompatibility (OSI)incompatibility (OSI) In this mechanism, pollen germinates and

reaches the ovule, but no fruit is set. LSI can be:

1.1. Pre-zygotic:Pre-zygotic: Deterioration of the embryo sac prior to pollen tube entry. Or

2.2. Post-zygotic:Post-zygotic: Malformation of zygote or embryo

Cont… The existence of LSI mechanism among the

different taxas and in general, is subjected to scientific debate:

Criticizers claim that the absence of fruit is due to the genetic defects, due to direct result of inbreeding depression

Supporters, on the other hand, argue for the existence of several basic criteria which differentiate LSI from inbreeding depression

Some other types of SI:

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 SI fruit trees, it is necessary to plant two cross-compatible varieties to ensure fruitfulness

2. SI may be used in Hybrid seed production. For that, two SI but cross compatible lines are to be interpolated; seeds obtained from both the lines would be Hybrid seed

3. SI provide a way for Hybrid seed production without emasculation

Cont…

4. SI 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.

Limitations of Self-incompatibility1. It is very difficult to produce homozygous

inbred lines in a self-compatible species2. Bud pollination has to be made to maintain

the parental lines3. SI is effected by environmental factors such

as temperature and humidity. Incompatibility is reduced at high temperature and humidity

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

References www.wikipedia.com www.theagricos.com www.agriinfo.in Principles of Plant Breeding by B. D. Singh

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