Self-incompatibility (SI) is the inability of a plant to produce seeds from its own pollen, affecting around 70 families of angiosperms and facilitating cross-pollination for increased genetic diversity. SI mechanisms can be categorized into heteromorphic and homomorphic systems, with different types based on genetic and site expression factors. Management strategies such as bud pollination, irradiation, and in vitro fertilization can break down SI, which is crucial for hybrid seed production in certain species while presenting challenges in breeding programs due to environmental influences.

1. Assignment
on
Self-incompatibility

2. • self incompatibility refers to the inability of plant to
set seed with functional pollen after self polllination.
• Koelreuter -1st reported S.I in Verbascum phoeniceum
plants(18th century)
• Self incompatibility reported in about 70 family of
angiosperm including several crop spp.
• It is importnant for outbreeding mechanism(cross
pollintaion) for normal fruit set.
• It maintained high degree of heterozygosity and can
take place any stage between pollination and
fertilization.

4. • Self incompatible pollen grain may fail to germinate on
the stigmatic surface.
• Some may germinate but fails to penetrate the stigmatic
surface.
• Some pollen grains may produce pollen tube, which
enters through stigmatic surface, but its growth will be
too slow. By the time the pollen tube enters the ovule
the flower will drop.
• Some time fertilziation is effected but embryo
degenerates early.

8. • According to Lewis (1954) the self incompatibility is
classified as follow
Self incompatibility
Heteromorphic system Homomorphic system
Distyl Tristylty Gametophytic S.I Sporophytic S.I

9. Other classification of S.I
S.R no Basis of
classification
Types of S.I Brief description
1 Gene involved monoallelic S.I controlled by single gene
Diallelic S.I controlled by two gene
polyallelic S.I controlled by several genes
2 Site of expression Stigmatic S.I gene express in the stigma
Stylar S.I gene express in the style
ovarian S.I gene express in the ovary
3 Pollen cytology Binucleate The pollen grains have 2 nuclei
trinucleate The pollen grains have 3 nuclei

10. • In this case there will be difference in the morphology of the
flowers. For example in Primula sp there are two types of
distyly flowers namely PIN and THRUM.
(Pin flower) (Thrum flower)

11. Mating
progeny
Phenotype genotype genotype phenotype
Pin x Pin ssx ss incompatibility -
Pin x Thrum SS xSs 1:1(pin:Thrum) 1 pin and 1 Thrum
Thrum x Pin Ss x ss 1:1(pin:Thrum) 1 pin and 1 Thrum
Thrum x Thrum Ss x Ss incompatibilty -

12. is known in some plants like Lythrum salicaria.
In this case the style of the flower may be short, long or
medium length
Sporophitic S.I gametophitic S.I
(S.I is governed by genotype of (S.I is governed by the genetic
pollen producing plant). constitute of gamets)

15. • There are 2 type of events considered to
constitute basic of S.I
a)stimulation of unlike genotype
b)inhibit of like genotype
• 2 hypothesis proposed for explaining this S.I
mechanism(by bateman)
a)complementary hypothesis
b)oppositional hypothesis

16. • Proposed by bateman in 1952.
• S.I due to absence of stimulation by the pistil
on pollen growth in the like
genotype(S1S2xS1S2)
• Means S.I is due to absence of substance in
the pistil or pollen which are essential for
pollen tube penetration.

17. • It states that interaction between like
alleles(S1S2xS1S2) leads to production of
inhibitor which inhibit the growth of pollen tube
in the pistil.
• Interaction between like alleles, a substance is
produced in pollen and pistil which property to
interfere with normal metabolism of pollen grain
and tube(inhibit enzyme or auxin, block pollen
tube membrane, inhibit enzyme necessary for
penetration.)

18. 1) Bud pollination:-pollination of immature buds
with mature pollen.
2) Delay pollination:-pollination of aged pistls
several days after maturity with normal
incompatible pollen.
3) Late season pollination:-self pollination at end
of flowering season also lead to seed set.

19. 1) Irradiation:-irradiation of style with X-ray immediately
before selfing reulst in break down of S.I.
2) High temp.:-treatment of high temp ranging from 30-60
degree leads to break down of S.I.
3) Mutilation of style:-S.I could be broken by mutilating
the stigma with steel wire brush during pollination.
4) Invitro-fertilization:-placing the pollen grains in direct
contact with ovules result in break down of S.I.

21. :-(cabbage and
brussel sprout hybrid seed production)
• Hybrid seed production without emasculation
and without resorting of CMS and GMS.
• Practiced in japan.

24. • S.I 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 spp.

25.  very difficult to produce homozygous inbreed
lines in a S.I spp.
 S.I is affected by environment factor i.e
Temperature and humidity and photo period.
 Sometimes, bees visit only one parental line
in the seed production plot resulting in sib
matting.

28. • No seed set in self
pollination but possible in
cross pollination
• S.I can utilized during hybrid
seed production
• S.I is less used because most
of crop has no S.I
• Un-functional pollen failure
to set seed both in self and
cross pollination.
• M.S can utilized during
hybridization programme of
breeding.
• M.S can used more.