Inability of a plant with functional pollen to set seed when self-pollinated. Hindrance to self-fertilization. Prevents inbreeding and promotes outcrossing. Reported in about 70 families of angiosperms including crop species.

1. Self-incompatibility in Plants;
Pseudoalleles, Isoalleles
STUDENT COURSE TEACHER
Miss. RUPIKA S Dr. M. KANIMOLI MATHIVATHANA
ID. No. 2017021055 Assistant Professor
Plant Breeding and Genetics
COLLEGE OF AGRICULTURAL TECHNOLOGY
(Affiliated to Tamil Nadu Agricultural University, Coimbatore)
(Accredited to Indian Council of Agricultural Research, New Delhi)
Kullapuram, Via Vaigai dam, Theni-625562

2. What is Self-incompatibility?
Inability of a plant with
functional pollen to set
seed when self-pollinated.
Hindrance to self-
fertilization.
Prevents inbreeding and
promotes outcrossing.
Reported in about 70
families of angiosperms
including crop species.

3. HISTORY OF S.I
First discussion on SI by
Darwin (1877).
 SI was coined by Stout
(1917).
First reported SI by
Kolreuter in the middle of
18th century in Verbascum
phoenicieum plants.
Reported SI in flowering
plants by East (1940).
Kolreuter

4. General features of S.I
Prevents selfing and promotes out-crossing.
Increases heterozygosity and reduces homozygosity.
Causes may be morphological, physiological, genetical
or biochemical.
SI can operate at any stage between pollination and
fertilization.
Normal seed set on cross pollination.
In plants, SI is governed is often inherited by a single
gene (S) with multiple alleles (S1,S2,S3 etc,) in the
species pollination.

5. CLASSIFICATION OF S.I:

7. Heteromorphic system
Distyly:
Two types of styles (long
and short) and stamens
(low and high).
Seen in Primulaceae
family.
In Primula, there are 2
types of flowers:
Thrum type- Has short
style and high anthers.
Pin type- Has long style
and low anthers.

8. Thrum and Pin type

9. Heterostyly in Primula

11. Thrum type Pin type

12. Tristyly:
Style and anther have 3
positions, viz. short,
medium and long.
Common in the family
Lythraceae (Lythrum
salicaria).
Controlled by two
genes(Ss and Mm).
S – short style,
s and M – medium style,
S and m – long style.

13. Tristyly

14. Distyly and Tristyly

15. HOMOMORPHIC SYSTEM
Self-fertilization inhibition depends on genetic or
biochemical or physiological mechanisms.
Mostly seen in crop plants.
It occurs in various ways,
• Pollen grains do not germinate on the stigma of same
flower.
• Even if they germinate, the pollen tube fails to
penetrate the stigma. Eg:Rye,Cabbage,Radish.
• If penetrates, pollen tube growth retards or very slow
rate of pollen tube growth occurs.
• No release of male gametes from the pollen tube
having normal growth.

16. Homomorphic S.I

18. Gametophytic S.I
• Governed by genotype of pollen.
• Stima is smooth and wet.
• Pollen tube inhibition in style.
• Pollen-Pistil interaction is governed by
haploid genome of each male gametes
and diploid genome of pistil tissue
(Haplo-Diplo).
• 1st discovered by East and Mangelsdorf in
Nicotiana sanderae .
• Reported in rye, red clover, white clover,
potato, tomato etc,.

19. Sporophytic S.I
 Governed by genotype of pollen
producing plant.
 Stigma is papilate and dry.
 Pollen germination, tube entry inhibited
on the stigmatic surface.
 Pollen-Pistil interaction govern by genome
of the plant on which the male and female
gamete produced (Diplo-Diplo).
 1st discovered by Hughes and Babcock
(1950) in Crepis foetida and Gerstel
(1950) in Parthenium argentatum.
 Reported in radish, cabbage, cauliflower,
sunflower, cosmos etc,.

20. Mechanism of S.I
Complementary hypothesis:
 Proposed by Bateman in
1952.
 S.I is due to absence of
stimulation by the pistil or
pollen in the like
genotypes(S1S2xS1S2)
which are essential for
pollen tube penetration.
Oppositional hypothesis:
 Interaction between like
alleles,(S1S2xS1S2) leads
to production of inhibitor
in pollen and pistil which
inhibits enzyme or auxin,
block pollen tube
membrane, inhibit enzyme
necessary for pollen tube
penetration.

21. Site of Gene Expression
• S.I may express only at three different locations in the
flower;
 Stigmatic inhibition:
Inhibition of pollen germination or pollen tube growth
in the stigmatic surface in S.I plant species with
trinucleate pollen (except Oenothera sp.)
 Stylar inhibition:
Inhibition of pollen tube growth in the stylar region
in S.I plant species with binucleate pollen.
 Ovarian inhibition: In some species, S.I reaction
occurs only when the pollen tube reaches the ovary.
Reported in Theobroma cacao.

22. How to overcome S.I?
 Bud pollination
 Delayed pollination
 Late season pollination
 Irradiation
 High temperature
 Mutilation of style
 In vitro fertilization.

23. Utilization in Plant Breeding
1. Production of Hybrids: S.I helps in hybrid seed
production without emasculation and without resorting to
genetic or CMS. Eg: Commercial hybrids in Brassica
(cabbage and Brussels sprouts) and Sunflower.
2. Combining Desirable Genes: S.I permits combining
desirable genes in a single genotype from two different
sources through natural cross pollination. It helps fruit
growers to increase yield by providing suitable pollinators.

25. LIMITATIONS IN S.I
• Very difficult to produce homozygous inbred
lines in a S.I species.
• Affected by environmental factors such as
temperature and humidity.
• Sometimes, bees visit only one parental line
in the seed production plot resulting in sib-
mating. Eg: Brussels sprouts.

26. Pseudoalleles
 Two genes with similar
functions located so close
to one another on a
chromosome that they are
genetically linked.
 Affect the same
character.
 Given by Morgan(1928)
and Lewis(1948).
 Pseudoallelic series or
complex series.
 Eg: Affect pigmentation in
Drosophila.
Drosophila melanogaster

27. Isoalleles
An allele considered as a normal but can be
distinguished from another allele by its differing
phenotypic expression when in combination with
dominant gene.
2 types:
If the phenotype is wild, these are normal or wild
alleles.
If the phenotype is mutant, these are called mutant
alleles.

28. References
Phundan Singh, 2015, Essentials of Plant Breeding, Sixth Revised Edition,
Kalyani Publishers, New Delhi, Pp:76-87.
Seiji Takayama, Hiroshi Shiba, Megumi Iwano, 2000, Proceedings of the
National Academy of S ciences 97(4).
Emma E Goldberg, Joshua R Kohn, Russell Lande, Kelly A Robertson,
Stephen A Smith,2010, Science 330 (6003),Pp:493-495.
Silva NF, et al. Cell Mol Life Sci. 2001 Dec;58(14):1988-2007, Mechanisms
of self-incompatibility in flowering plants, York University, Canada.
https://www.sciencedirect.com

29. https://www.biology-pages.info
https://www.merriam-webster.com
Lewis. E. B, PSEUDOALLELISM AND GENE EVOLUTION, 1951, Cold
Spring Harbor Symposia on Quantitative Biology, Pp:159-174.
https://hal.archives-ouvertes.fr
https://www.nature.com
https://doi.org/10.1017/S0016672300011459
https://biocyclopedia.com >genetics
www.notesonzoology.com>genetics