This document discusses self-incompatibility in plants. It begins by defining self-incompatibility as the prevention of fertilization after self-pollination. There are two main types of self-incompatibility systems - homomorphic and heteromorphic. Heteromorphic systems involve morphological differences between flowers like distyly seen in Primula, while homomorphic systems do not. Homomorphic systems include gametophytic and sporophytic self-incompatibility, which differ in how the incompatibility reaction is controlled. Self-incompatibility promotes outbreeding and maintains genetic diversity in plant species. It has applications for plant breeding through hybrid seed production.

1. SELF-INCOMPATIBILITY
SanjayKumarBishnoi
Ph. D. ResearchScholar
SKRAU, Bikaner

2. INTRODUCTION
• Self-incompatibility- Prevention of fusion of fertile male and female gametes after self-
pollination (Growers,1998)
• Koelreuter in the middle of 18th century, first reported self incompatibility in Verbascum phoeniceum
plant.
• Term first coined by Stout in 1917.

3. CAUSES OF SELF-INCOMPATIBILITY
• Pollen grain fails to germinate on stigma
• Pollen tube fails to enter the stigma
• Slow growth of tube
• Embryo degenerate at early stage

4. FEATURES OF SELF-INCOMPATIBILITY
• It is an important outbreeding mechanism which prevents autogamy and
promotes allogamy.
• Do not produce seed on self pollination but lead to normal seed set on cross
pollination.
• Maintains high degree of heterozygosity in a species due to outbreeding and
reduces homozygosity due to elimination of inbreeding or selfing.

5. Given by Lewis, 1954

6. HETEROMORPHIC SYSTEM
Flowers of different in morphology is called heteromorphic
system.
1. DISTYLY- e.g. Primula
• 2 types of flowers
• Pin flower- long styles and short stamens
• Thrum flower- short styles and long stamens.
• Compatible mating is only between pin and thrum flowers
• This system is of little importance in crop plants ; it occurs in
sweet potato and buckwheat.

7. Results of four types of crosses in Primula
Crosses between Genotypes Results
Pin * Pin ss * ss Incompatible
Thrum * Thrum Ss * Ss Incompatible
Thrum * Pin Ss * ss 1 Thrum : 1 Pin
Pin * Thrum ss * Ss 1 Thrum : 1 Pin

8. 2. TRISTYLY- e.g. Lythrum salicaria
• Styles are of 3 different length- short , medium and
long
• It is controlled by 2 dominant genes – S and M. (S-
short style , M- medium style)
• The compatible matings are- long * medium, long *
short, medium * short

9. HOMOMORPHIC SYSTEM
• Incompatibility is not associated with morphological differences among flowers.
• Two types:-
1. Gametophytic self incompatibility
2. Sporophytic self incompatibility
1. Gametophytic self incompatibility
• The incompatibility reaction of pollen is controlled by its own genotype.
• Pollen tube growth is usually inhibited in the style or ovary.
• First described by East and Mangelsdorf in 1925 in Nicotiana sanderae.
• Most widely distributed and ancestral.
• e.g.-potato, tomato, rye, beet, pine apple etc.

10. • Three types of mating-
• i) Fully incompatible = S1S2 x S1S2
• ii) Partially compatible = S1S2 x S2S3
• Iii) Fully compatible = S1S2 x S3S4

11. 2. Sporophytic self-incompatibility
(SSI)
• The incompatibility reaction of pollen is
controlled by the genotype of the plant on
which the pollen is produced called
sporophytic self-incompatibility.
• First reported by Hughes and Babcock in
1950 in Crepis foetida, and by Gerstel in
Parthenium (in the same year).
• e.g.- radish (R. sativus), diploid Brassica
crops, cabbage, cauliflower, sunflower etc.

12. APPLICATIONS OF SELF - INCOMPATIBILITY
1. Production of hybrids
2. Multiplication of inbred lines
3. Creation of variability
ACHIEVEMENTS OF S.I.
Crop Variety
Cauliflower Pusa Hybrid-2, Snow Queen, Snow King, White Contessa
Cabbage BRH-5, H-44,H-43, Pusa Synthetic, Meenakshi