Self-incompatibility 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.

1. Topic: Self-Incompatibility
in Plants.
Course: GP-503 - Principles of
Plant Breeding(2+1)
Course Teacher: Dr. J. N. Patel
Prepared By,
MAYUR KUMAR SONAGARA
MSc. (Agri) Genetics And Plant
Breeding

2. SELF INCOMPATIBILITY
• Self-incompatibility 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.

3.  Self incompatibility is an important out breeding
mechanism, which prevent auto gamy and produce
allogamy. It has reported in more than 300 species
belonging to 70 families. In self incompatibility non-
fruitfulness or failure of fruit setting May occurs due
to:
 Pollen grain fails to germinate on the stigma.
 Pollen grain germinates, but pollen tube fails to
enter inside the stigma and style.
 Sometimes pollen tube enters inside the style but
growth is very slow.
 Pollen tube enters the ovule but there is no
fertilization due to degeneration of eggs cells.
 Sometimes fertilization is effected but embryo
degenerate at very early stage.

4. • Joseph Gottlieb Kölreuter (27 April
1733 – 11 November 1806), was
a German botanist who pioneered the study
of plant fertilization, hybridization and was
the first to detect self-incompatibility.
• Self incompatibility was first reported by
KOELREUTER in middle of eighteenth
century. More then 30 speices belonging to
70 families of angiosperms show self
incompatibility.
Verbascumphoeniceumplant(18th
century)
HISTORY

5. • First discussion on self incompatibility by DARWIN.
(1877)
• The term self-incompatibility was given by STOUT
(1917)
• BATEMAN (1952,1953,1954) gave explanation on
incompatibility in brassicas plants, namely Iberis
amara L., Raphanus sativus L., Brassica campestris L.,

6. GENERAL FEATURES OF SELF
INCOMPATIBILITY
• Prevents selfing and promotes outbreeding so
increases the probability of new gene combinations
• Causes may be morphological, physiological,
genetical or biochemical
• Normal seed set on cross pollination
• May operate at any stage between pollination and
fertilization
• Reduces homozygosity
• In plants, self-incompatibility is often inherited by a
single gene (S) with different alleles (e.g. S1, S2,
S3 etc.) in the species population

7. Mechanisms of single-locus
Self-incompatibility
• The best studied mechanisms of SI act by inhibiting the
germination of pollen on stigmas, or the elongation of the
pollen tube in the styles. These mechanisms are based
on protein-protein interactions, and the best-understood
mechanisms are controlled by a single locus termed S,
which has many different alleles in the species population.
Despite their similar morphological and genetic
manifestations, these mechanisms have evolved
independently, and are based on different cellular
components; therefore, each mechanism has its own,
unique S-genes.

8.  The S-locus contains two basic protein coding regions - one
expressed in the pistil, and the other in the anther and/or
pollen (referred to as the female and male determinants,
respectively). Because of their physical proximity, these are
genetically linked, and are inherited as a unit.
The units are called S-haplotypes.
 The translation products of the two regions of the S-locus are
two proteins which, by interacting with one another, lead to
the arrest of pollen germination and/or pollen tube
elongation, and thereby generate an SI response, preventing
fertilization. However, when a female determinant interacts
with a male determinant of a different haplotype, no SI is
created, and fertilization ensues.

9. • On the basis of interactions between pollen
grains and pistils, S.I is classified into the
following two types;
I. Complementary
system of S.I
Self-incompatibility
II. Oppositional
system of S.I

10. • Complementary System of self
incompatibility
This system is also called stimulatory type of
self- incompatibility.
In this system pollen together provide substances,
which stimulate pollen germination and growth of
the pollen tube if the pollen grains differ in S.I
genotype from that of the pistils; the germination
and growth of pollen having similar genotype is
not stimulated. The complementary type of self
incompatibility occurs in Dendrobium, where
incompatibility leads to flower abscission.

11. • Oppositional System of self incompatibility
This system is also known as inhibitory type of
self incompatibility.
In this system pollen and pistil produce such type
of substances, which prevents pollen germination
or pollen tube growth if the pollen has same S.I
reaction as pistil.
Almost all the cases of Self Incompatibility are of
this type.

12. CLASSIFICATION
• LEWIS (1954) has suggested the various
classifications of self incompatibility
1) ) Single-locus self-incompatibility
• Gametophytic self-incompatibility (GSI)
• Sporophytic self-incompatibility (SSI)
2) Two locus gametophytic self-incompatibility.
3) Heteromorphic self-incompatibility.
4) Cryptic self incompatibility (CSI)
5) Late-acting self-incompatibility (LSI)

13. Heteromorphic System of
Self-Incompatibility
• Heteromorphic self incompatibility is associated
with flower morphology, exists in heterostylous
flowers. Do not have much importance in crop
plants.
• The genes responsible for self-incompatibility in
heterostylous flowers are strongly linked to the
genes responsible for flower polymorphism, so
these traits are inherited together.
• The associated concepts are distyly and tristyly.

14. Distyly
• Here, both stamens and styles are of
two types.
• Stamens may be low and high; styles
short and long. It is determined by a
single gene, with two alleles.
• The flower with short style and high
stamen is called as thrum type and
flower with long style and low
stamen is called as pin type. Both
thrum and pin flowers differ for six
characters in addition to stamen and
style length.

15. Tristyly
• In tristyly, styles and stamens have three different
positions.
• It is determined by two genes S and M, each with
two alleles. S gives rise to short style, S and M to
medium style and 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.

16. Short Style Medium Style Long
Style

17. • Distyly and tristyly has been reported in Primula
and Evening primrose respectively.

19. • In this system, flowers of different
incompatibility groups are different in
morphology. E.g In Primula there are two types
of flowers. Pin and thrum. Pin flowers have long
style and short stamens. While thrum flowers
have short styles and long stamens. This
situation is referred as distyly. Tristyly is known
in some plant species. E.g Lythrum in such case,
the style of a flower may be either short long or
of medium length. In the case of distyly, the only
compatible mating between pin and thrum
flower.

20. Homomorphic System of
Self-Incompatibility
• In the Homomorphic system incompatibility is
not associated with morphological differences
among flowers.
• The incompatibility reaction of pollen may be
controlled by the genotype of the plant on which
it is produced (Sporophytic control) or by its
own genotype ( Gametophytic control).

21. a) Gametophytic System:
• Gametophytic incompatibility was first described by
East and Mangelsdor in 1925 in Nicotiana sanderae.
• The incompatibility reaction of pollen on which it is
produced. Generally, incompatibility reaction is
determined by a single gene having multiple alleles.
E.g. Potatoes, Wild tomatoes, Tobacco, Roses, Bajara,
Rye, Sugar beet.
• Family wise, in Solanaceae, Scrophulariaceae, Poaceae,
Fabaceae, Campanulaceae, Onagraceae, Papaveraceae
and Rosaceae.
• Sometimes , polyploidy may lead to a loss of
incompatibility due to a competition between the two S
alleles , present in diploid pollen, irradiation of pollen
or buds with X rays or gamma-rays temporarily
suppresses the incompatibility style.

22. • Pollen tube grows very slowly in the style
containing the same S allele as the pollen and
fails to effect fertilization. Therefore all the
heterozygous at the S locus. In a single system
there are three types of matings.
1) Fully Incompatible (S1 S2 X S1 S2)
2) Fully Compatible (S1 S2 X S3 S4)
3) Partially Compatible (S1 S2 X S2 S3)

23. b) Sporophytic System:
• In the Sporophytic system also, the self incompatibility
is governed by a single gene. ‘S’ with multiple alleles,
more than 30 alleles are known in Brassica oleracea.
• In general, the number of S alleles is considerably
larger in Gametophytic than in the Sporophytic system.
The incompatibility 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.
• Eg. Brassicaceae, Polemoniaceae, Caryophyllaceae,
Betulaceae, Asteraceae, Sterculiaceae and
Convolvulaceae

24. • Hughes and Babcock first reported it in 1950 in Crepis
foetida and by Gerstel in Parthenium argentatum. In the
Sporophytic system, the alleles may exhibit dominance,
co-dominance or competition. Consequently, there may be
much complex incompatibility relationship.
• Lewis has summarised the following characteristics of
this system.
1. There are frequent reciprocal differences.
2. Incompatibility can occur with the female parent.
3. A family can consist of three incompatibility groups.
4. Homozygotes are a normal part of the system.
5. As incompatibility is found in radish ( R.sativus),
diploid Brassica crops. In many cases, different S alleles
vary in their activity leading to varying degree of self-
incompatibility. E.g, Brasicca oleracea.

25. • It is controlled by single gene S with multiple
alleles, where alleles may show individual
action, dominance or interaction in pollen or
style.
• S-locus is a cluster of three tightly-linked loci,
SLG (S-Locus Glycoprotein), SRK (S-Receptor
Kinase) and SCR (S-locus Cysteine-Rich
protein).
• SLG codes for a part of a receptor present in the
cell wall of the stigma; SRK codes for the other
part of the receptor and SCR codes for a secreted
ligand for the same receptor.

26. • 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. So, pollen grains (S1 or S2)
produced by S1S2 plant will germinate only on
S3S4 plant not on S1S2 or S1S3and so on. Order of
dominance followed is S1 >S2> S3> S4 .

28. 28

29. Cryptic Self-Incompatibility
(CSI)
• In this mechanism, the simultaneous presence of
cross and self pollen on the same stigma, results
in higher seed set from cross pollen, relative to
self pollen. However, as opposed to 'complete' or
'absolute' SI, in CSI, self-pollination without the
presence of competing cross pollen, results in
successive fertilization and seed set in this way,
reproduction is assured, even in the absence of
cross-pollination.

30. • CSI acts, at least in some species, at the stage of
pollen tube elongation, and leads to faster
elongation of cross pollen tubes, relative to self
pollen tubes.
• The strength of a CSI response can be defined, as
the ratio of crossed to selfed ovules, formed
when equal amounts of cross and self pollen, are
placed upon the stigma.

31. Late-Acting Self-incompatibility
(LSI)
• It is also termed ovarian self incompatibility
(OSI). In this mechanism, self pollen
germinates and reaches the ovules, but
no fruit is set. LSI can be pre-zygotic (e.g.
deterioration of the embryo sac prior to pollen
tube entry, as in Narcissus triandrus) or post-
zygotic (malformation of the zygote or embryo)

32. Relevance of Self Incompatibility:
• Self incompatibility effectively prevents self
pollination. As a result, it has a profound effect
on breeding approaches and objectives.
1. In self – incompatible fruit trees, it is
necessary to plant two cross compatible
varieties to ensure fruitfulness.
2. Self incompatibility may be used in hybrid seed
production. For that Two self incompatible,
but cross – compatible, Lines are inter planted,
seed obtained from both the lines would be
hybrid seed.

33. 3.Self incompatibility provide way for hybrid seed
production without emasculation and without
restoring to the genetic and cytoplasmic male sterility.
4. Schemes for the production of double cross and triple
cross hybrids have also been proposed and their
feasibility has been demonstrated in the case of
Brassicas.
5. In case of pineapple, commercial clones are self
incompatible. As a result, their fruits develop
parthenocarpically and are seedless.
6. Self incompatibility 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.

34. Limitations Of Self Incompatibility
1. It is very difficult to produce homozygous
inbred line in a self compatible species.
2. Bud pollination has to be made to maintain the
parental lines.
3. Self incompatibility is affected by
environmental factors such as temperature and
humidity.
4. There is limited use of self incompatibility due
to problems associated with the maintenance of
inbred line through hand pollination as it is
tedious and costly.

36. Temporary suppression of Self
Incompatibility
• In the many situations eg., during the
production of inbreds for use a parents in hybrid
seed production, it is the essential that
temporary self-fertility is achieved in a manner
so that self- incompatibility is fully functional in
the selfed progeny.
• Such self-fertility is known as pseudofertility and
is achieved by temporarily supressing the
incompatibility reaction using one of the
following tecniques.

37. 1. BUD POLLINATION: Bud pollination
means application of mature pollen to
immature non receptive stigma, generally 1-2
days prior to the anthesis. This is most
practicable and successful method both in the
gametophytic and sporophytic systems.
2. SURGICAL TECHNIQUE: Rmoval of the
stigmatic surface, the whole of the stigma or a
part or whole of the style may permit an
otherwise incompatible mating.
3. DELAY POLLINATION: Pollination of aged
pistils several days after maturity with normal
incompatible pollen.

38. 4. LATE SEASON POLLINATION: Self pollination at the
end of flowering season leads to reduction in self
incompatibility and result into seed set.
5. IRRADIATION: In single-locus gametophytic system,
e.g., in Solanaceae, acute radiation with X-rays or gamma
rays induces a temporary loss of self incompatibility.
6. HIGH TEMPERATURE: In some species, Trifolium,
Lycopersicon, Brassica etc., exposer of pistils to
temperature 60 degree Celsius induces pseudo-fertility.
7. DOUBLE POLLINATION: In some species self
incompatibile mating become possible when
incompatible pollen in applied as a mixture with a
compatible pollen, or it is applied after pollination with a
compatible pollen.

39. ELIMINATION OF SELF
INCOMPATIBILITY
In the case of single locus Gametophytic system,
1) Incompatibility may be eliminated by doubling
the chromosome number.
2) Isolation of self-fertile (Sf) mutations is a very
useful tool in the elimination of self
incompatibility.

40. SUMMARY
• Self incompatibility is inability of pollen to
fertilize same flower or flower of other plant.
There exist two system of S.I Complementary and
Oppositional on the basis of pollen and pistil
interaction.
• On the basis classification there are S.I may be
heteromorphic and homomorphic.
Heteromorphic system shows sporophytic control
of pollen incompatibility reaction. But the
homomorphic system exhibit both gametophytic
and sporophytic controls.

41. • Cryptic S.I is also there in which cross and self
pollen play there part. In Late Acting S.I self
pollen success to reach at ovule but not able to
set fruit.
• S.I has many applications in Plant breeding by
helping in production of hybrid seeds between
two non compatible plant species by combinig
desirable genes.
• Using various method like bud pollination,
surgical technique, high temperature,
irradiation, late season pollination and double
pollination we can temporaily supress the self
incompatibility.

42. MULTIPLE CHOICE QUESTIONS
• Q1.In self incompatibility system
A. Pollen not produce.
B. Self pollination takes place.
C. Pollen does not germinate on self pollinaton.
D. All are correct.
Ans D.

43. • Q2.In tristyly, how many different positions are
acquired by the stamens and styles, including how
many types of genes respectively.
A. 2 and 3
B. 3 and 2
C. 3 and 3
D. 2 and 4
Ans. B (Three different types of positions of stamen
and style including S and M genes)

44. • Q3. Flower with short style and high stamen is
called as and flower with long style and low
stamen is called as respectively?
A. Thrum type & pin type
B. Pin type & thrum type
C. Thrum type & thrum type
D. None of the above
Ans. A

45. • Q4. Which of the following plants is not self-
incompatible?
• A. Carrot
• B. Tomato
• C. Radish
• D. Cucumbers
• E. Papaya
• Ans. B

46. Q5.Can self-compatible plants also accept
"foreign" pollen?
• A. Yes
• B. No
• C. May or May not
• D. Only if it is an apple
• Ans. A ('Big Boy' tomato accept "early girl"
tomato)

47. • Q6.In Gametophytic S.I system the growth of the
pollen tube arrests where?
A. on the stigma Surface
B. All of the above
C. Near to ovule
D. In the style
Ans. D

48. • Q7. Which one is true for Sporophytic
incompatibility?
A. S1S2 X S1S2 = Compatible
B. S1S2 X S2S3= Compatible
C. S1S2 X S3S4= Compatible
D. S1S2 X S2S1= Compatible
Ans. C

49. • Q8.In Sporophytic S.I system the growth of the
pollen tube arrests where?
A. On the stigma Surface
B. All of the above
C. Near to ovule
D. In the style
• Ans. A

50. • Q9. Which one is true for Sporophytic
incompatibility?
A. S1S2 X S1S2 = Compatible
B. S1S2 X S2S3= Compatible
C. S1S2 X S3S4= Non Compatible
D. S1S2 X S2S1= Compatible
• Ans. B

51. • Q 10. Late acting self incompatibility is also knpwn
as?
A. Male self incompatibilty
B. Gametophytic self incompatibility
C. Ovarian self incompatibility
D. Homomorphic self incompatibility
Ans. C

52. • Q11. Self incompatibility encourages which process
among the following?
A. Autogamy
B. Parthenogamy
C. Chasmogamy
D. Allogamy
Ans. D

53. • Q12. First time self incompatibility observed by
whom ?
A. Bateman
B. Koelreuter
C. Sampson
D. Brace
Ans. B

54. • Q13. Oppositional system of self incompatibility is
also known as?
A. Stimulatory type of S.I
B. Recessive type of S.I
C. Inhibitory type of S.I
D. Complementary type of S.I
Ans. C

55. Q14.Which type of interaction are responsible for
self incompatibility?
A. Protein-Protein interactions
B. Protein- fatty acid interactions
C. Protein-Lipid interactions
D. Protein-Vitamins interactions
Ans. A

56. • Q.15 In gametophytic self incompatibility S locus
products synthesis takes place after completion of
meiosis? This statement is
A. FALSE
B. TRUE
C. MAY BE TRUE
D. MAY NOT BE FALSE
Ans. B