2. SELF INCOMPATIBILITY
⚫ Self-incompatibility and male sterility are the two
mechanisms, which encourage cross pollination.
⚫ More than 300
families of angiosperms show
species belonging to 70
self
incompatibility.
⚫ First reported by Koelreuter in Verbascum
phoeniceum (18th century).
3.
4. Definition –
⚫ Self incompatibility refers to the “inability of
plant to set seed with functional pollen after
self pollination. ’’
⚫ Here, flowers will produce functional or viable
pollen grains which fail to fertilize the same
flower or any other flower of the same plant.
5. ⚫ Important for outbreeding mechanism
(cross pollination) for normal seed set.
⚫ Maintains high degree of heterozygosity.
⚫ Can take place at any stage between
pollination and fertilization.
6. CAUSES OF SELF
INCOMPATIBILITY
• Self incompatible pollen grain may fail to germinate on the
stigmatic surface- Pollen -stigma interaction
• Some may germinate but fails to penetrate the stigmatic surface-
Pollen -stigma interaction
• Some pollen grains may produce pollen tube, which enters
through stigmatic surface, but its growth will be too slow.
Pollen tube – style interaction
• Some time fertilization is occurs but embryo
degenerates early.- Pollen tube – ovule interaction
7. • There are 2 type of events or hypothesis
considered to constitute basic of S.I (by
Bateman)
a)Stimulation of unlike genotype /
complementary hypothesis
a)Inhibit of like genotype/
oppositional hypothesis
8. • 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.
9. • 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.)
10. CLASSIFICATION OF S.I
•According to Lewis (1954) self- incompatibility
can be classified as follows ;
SELF INCOMPATIBILTY
Heteromorphic system Homomorphic system
Gametophytic Sporophytic
Distyly Tristyly
11. HETEROMORPHIC SYSTEM
□ In this case difference in the morphology of the
flowers are observed.
□For example in Primula spp there are two types of
flowers namely PIN and THRUM.
Pin flowers - long styles and short stamens
Thrumflowers- short styles and long stamens.
□This situation is referred to as distyly.
13. □In distyly, the only compatible mating is between pin
and thrum flowers.
□Governed by a single gene “s”
Ss produces thrum, while
ss produces pin flowers.
Allele S is dominant over s.
14. RESULTS OF 4 TYPES OF MATING IN
PRIMULA
MATING PROGENY
Phenotype Genotype Phenotype Genotype
Pin x Pin ss x ss Incompatible mating ------
Pin x Thrum ss x Ss 1 Ss : 1ss 1 Thrum : 1 Pin
Thrum x Pin Ss x ss 1Ss : 1ss 1 Thrum : 1 Pin
Thrum x Thrum Ss x Ss Incompatible mating --------
Distyly is controlled by a complex locus "s" having 2
alleles S and s
15. □Tristyly
in some plant species, e.g.
Lythrum
✔ Known
✔ Style of a flower may be either
▪ short,
▪ Long
▪ medium length.
16. HOMOMORPHIC
SYSTEM
Sporophytic SI
(governed by
genotype of pollen
producing plant).
Gametophytic SI
(governed by the
genetic constitution
of gametes)
Here,incompatibility -not associated with
morphological differences among flowers.
17. Gametophytic System
□First described by East and Mangelsdorf in 1925 in
Nicotiana sanderae.
□Incompatibility reaction of pollen is determined by
its own genotype, and not by the genotype of the plant
on which it is produced.
□Generally, incompatibility reaction is determined
by a single gene having multiple alleles,
18. □ If same allele as that of a pollen is present in the stylar tissues, it
opposes the growth of pollen tube in the style.
□ So, gametophytic incompatibility is also called as
‘oppositional factor system’.
There are three types of mating system
• Fully incompatible, e.g., S1S2 x S1S2
• Fully compatible, e.g., S1S2 x S3S4
•Partially (i.e., 50% of the pollen
compatible,) e.g., S1S2 x S2S3
20. Sporophytic self incompatibility system
• .Theincompatibility reaction of pollen is governed by the
genotype of the plant on which the pollen is produced,
and not by the genotype of the pollen.
□ First reported by Hughes and Babcock in 1950 in Crepis
foetida, and by Gerstel in Parthenium argentatum.
23. Elimination of Self-Incompatibility
Temporary suppression of self incompatibility-
1. Surgical Techniques- removal of stigmatic surface E.g.- Brassica or removal of
style E.g.- Petunia
2. Bud Pollination- Pollination of immature bud with mature pollen
3. End-of-Season Pollination- In some cases SI is reduced towards the end of
flowering period. Pollilation at this time may be successful.
4. High Temperature- Exploring the pistill to 60 degree C will induce pseudo fertility
5. Irradiation
6. Grafting- Grafting of branch to another branch.
7. Double Pollination- Application of mixture of incompatible and compatible pollen
grain
1. By doubling the chromosome number we can eliminate self
incompatibility
2. By inducing mutagenesis to produce self fertile lines
3. By transferring self compatible alleles from related species through back
cross breeding
24. Relevance of Self-Incompatibility
• Production of hybrids :-(cabbage and Brussels sprout
hybrid seed production)
• Hybrid seed production without emasculation and without
resorting of CMS and GMS.
• Practiced mainly in Japan.
25.
26. 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.
