Self incompatibility in plants

self incompatibility,classification

1. T.C.B College of Agriculture
and Research Station,
Bilaspur
Chattisgarh
Presented To; Presented By;
Dr.Roshan Parihar SHEKH ALISHA
Dept.of Plant Breeding BSc Ag 2
nd
yr 2
nd
sem..
Self
IncompatIbIlIty

2. •If a plant does not set seed when pollinated
with its own functional pollen, but exhibits
normal seed setting when cross pollinated,it
indicates presence of SELF INCOMPATIBILITY.
•SELF INCOMPATIBILITY refers to the inability
of a plant with functional pollen to set seeds
when self pollinated.
•Term Self Incompatibility was originally coined
by Stout in 1917.

3. Features of
self-incompatibility
It is an important outbreeding mechanism ,prevents autogamy
& promotes allogamy
Maintains high degree of heterozygosity due to outbreeding &
reduce homozygosity due to elimination of inbreeding.
SI results due to morphological,genetic,physiological &
biological , chemical causes. Not under simple genetic control.
SI has been reported in 70 angiospermes including several
crop species.

4. 1.FLOWER MORPHOLOGY
•HETEROMORPHIC:
i.Distyly
ii.Tristyly
•HOMOMORPHIC:
i.Sporophytic
ii.Gametophytic
2.GENES INVOLVED:
a.Monoallelic b.Diallelic c.Polyallelic
3.SITE OF EXPRESSION OF SI REACTION:
a.Stigmatic b.Stylar c.Ovarian
4.POLLEN CYTOLOGY
a.Binucleate b.Trinucleate

5. When SI is associated with differences in Floral Morphology ,it is
known as Heteromorphic system.
SI results due to differences in the length of style and stamen.
System is again of two types:
1.DISTYLY
2.TRISTYLY
1.DISTYLY: It refers to two types of Styles (short& long) and Stamens
(low & high). The crosses are compatible only between the style and
stamen of matching length.
EXAMPLE: Primulaceae Family
2.TRISTYLY: When style has three different positions in flower viz
short, medium and long.
EXAMPLE: Lythraceae Family

6. In Homomorphic system, Self incompatibility results due to
physiological causes rather than differences in flower morphology.
In this system ,the plant do not have differences in the length of style
and stamens or other floral parts.
1.The pollen grains do not germinate on the stigma of same flower.If
they germinate the pollen tube fails to penetrate the stigma as in
Rye, Cabbage and Raddish.
2.The pollen grains may germinate but there in retardation of pollen
tube growth.
3.In some cases, there is slow rate of pollen tube growth and it rarely
reaches the ovary in time to effect self fertilization.
4.In some cases, pollen tube growth may be normal, but it does not
release the male gamete.

7. HOMOMORPHIC SYSTEM IS Of TwO TYPES:
1.GAMETOPHYTIC SYSTEM
2.SPOROPHYTIC SYSTEM
1.GAMETOPHYTIC SYSTEM
When SI is controlled by the genetic constitution of Gametes, it is
known as Gametophytic self incompatibility system.
FEATURES:
•SI in majority of species is governed by a single gene S, which
has large no. of multiple alleles. However, in rye SI reaction is
governed by 2 loci.
•In this system alleles have individual action in the style without
interaction.
•Pollen grains are unable to germinate or function on a pistil
having similar allele as that of pollen. The pollen tube growth is
usually inhibited in the style or ovary.
•Plant species belonging to GSI system have binucleate pollen.

8. 2.SPOROPHYTIC
SYSTEM
When the SI is governed by the genotype of pollen producing
plants (sporophytes), it is called sporophytic system.
FEATURES:
•In this system also SI is controlled by single gene S which has
multiple alleles.
•The alleles may show dominance, individual action or
interaction in either pollen or style as per the allelic
combinations involved.
•This system exhibits inhibition of pollen germination or pollen
tube growth on the stigma of same flower.
•Pollen grains from both heterozygous or homozygous plants
react in a similar fashion due to dominance effect of male
parent.
•Plant species of this system have trinucleate pollens.

9. GAMETOPHYTIC
(GSI)
outcome of the interaction between
the pollen tube and the style is
determined by the genotype of the
pollen (gamete)
S-locus products are synthesized
after completion of meiosis
growth of the pollen tube arrests in
the style
SPOROPHYTIC
(SSI)
outcome of the interaction between
the pollen tube and the style is
determined by the genotype of the
sporophyte (diploid tissue)
S-locus products are synthesized
before completion of meiosis
growth of the pollen tube arrests at
the surface of the stigma

10. 1.BUD POLLINATION
2.DELAYED POLLINATION
3.END SEASON POLLINATION
4.IRRADIATION
5.HIGH TEMPERATURE
6.MUTILATION OF STYLE
7.IN VITRO FERTILIZATION

11. Pollination of immature buds with mature pollen has been
successful in the production of large quantity of self seed both in
gametophytic & sporophytic systems in Brassica,Nicotiana &
Petunia.This method is now used for the development of inbred
lines for hybrid seed production in Brassica species.
This also leads to self fertilization in some
species.Pollination of aged pistils several days after
maturity with normal incompatible pollen resulted in some
degree of self fertilization in Brassica , Linum.

12. Self pollination at the end of flowering season also leads to
seed set in some species like Nicotiana, Petunia and
Abutilon.This may be due to loss of capacity to produce
active incompatibility substances at the end of flowering
season.
Irradiation of style with X- rays immediately before selfing
resulted in breakdown of self incompatibility in Petunia.
Gamma irradiation significantly increased seed setting upon
selfing in Lycopersicon Peruvianum. However, these effects were
observe in one generation & were lost in the next generation.
Mutation plays an important role in overcoming self
incompatibility.

13. Heat treatment inactivates he substance or enzyme which
causes self incompatibility.
Removal of stigma in species having stigmatic
incompatibility results in certain amount f seed production in
some crops. In this species, SI could be broken by
mutilating the stigma with steel wire brush during pollination
Placing of pollen grains in direct contact with ovules,
resulted in breakdown of self incompatibility in many crop
species.

14. Utilization
1.Production of Hybrids
2.Combining desirable genes
limitations
1.Difficult to produce homozygous inbred
line
2.Affected by environmental factors
Temperature,humidity
3.Sometimes bees visit only on one parental
line in the seed production plot resulting in
sib mating

15. Summary
●SI is an important mechanism for preventing
inbreeding in plants
●3 different mechanisms of SI have been
described at the molecular level
●Sporophytic SI dependent on a kinase-mediated
signaling cascade
●Gametophytic SI based on selective degradation of
pollen rRNA by S-RNases
●Gametophytic SI based on a calcium-dependent
(MAPK) signaling cascade leading to cell death in
pollen