5. 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)
6. 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
7. 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
8. Types of Self-incompatibility
1.1. 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)
9. 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.
10. 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
11. Cont…
2.2. Saprophytic Self-incompatibility:Saprophytic Self-incompatibility:
First introduced by HughesHughes and BabcockBabcock in 1950 in Crepis foetidaCrepis foetida
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
12. 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
13. 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 stamen
b.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
14. 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 alleles
1. S gives rise to short style
2. 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.
15. Late-Acting Self-incompatibility
It is also known as Ovarian Self-incompatibilityOvarian Self-incompatibility
(OSI)(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
16. 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
18. 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
19. 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.
20. Limitations of Self-incompatibility
1. It is very difficult to produce homozygous inbred
lines in a self-compatible species
2. Bud pollination has to be made to maintain the
parental lines
3. 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.
