self incompatibility
TRANSCRIPT
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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