💔 Self-Incompatibility

Learn abount Self-Incompatibility

Self-incompatible pollen grain does not germinate and if pollen grain germinates, its pollen tube fails to enter into stigma. If pollen tube enters into stigma and fertilization takes place but ultimately embryo aborts. It means any how embryo does not develop and occurrence of self-incompatibility is due to biochemical reaction but its precise nature is not clearly understood.
On the basis of the interaction between pollen grains and pistil, it is of two types:
- Complementary i.e. stimulatory type where pistil & pollen stimulate each other or either. e.g. Dendrobium.
- Oppositional i.e. inhibitory type where pistil & pollen inhibit each other or either. Almost all the cases of self-incompatibility are inhibitory type.
Lewis (1954) suggested various types of classifications of self-incompatibility (SI). A simpler classification is:

Flowers of different incompatibility groups are different in morphology.
The compatibility reaction of pollen is determined by the genotype of the plant producing them. The incompatibility system is heteromorphic-sporophytic.

Here morphological differences between flowers is not associated with incompatibility. The incompatibility reaction of pollen is either controlled by the genotype of the plant on which it is produced (sporophytic control) or by its own genotype (gametophytic control).
- Gametophytic system: East and Mangelsdorf (1925) firstly described Gametophytic incompatibility in Nicotiana sanderae. The incompatibility reaction of pollen is determined by its own genotype and not by the genotype of the plant on which it is produced. e.g. pineapple, ryegrass, diploid coffee, diploid clovers (Trifolium sp.) etc.
- Sporophytic system: First time this system was reported, by Hughes & Babcock (1950) in Crepis foetida and by Gerstel (1950) in Parthenium argentatum. The incompatibility reaction of pollen is determined by the genotype of the plant on which the pollen is produced and not by the genotype of the pollen.

By doubling the chromosome number in single locus gametophytic system.
Isolation of self-fertile mutations (very useful tool)
The transfer of self-compatibility alleles from a related species through a back cross programme.

For the production of inbred (for hybrid seed production) it is essential to achieve self-fertility, where self-incompatibility is fully functional in the selfed progeny. This self-fertility is called as pseudo fertility. This pseudo fertility is achieved through temporary suppression of incompatibility by one of the following techniques:
Bud pollination: Means application of mature pollen to immature non-receptive stigma generally 1-2 days before anthesis. Bud pollination is the most practicable & successful method in both gametophytic and sporophytic systems.
Surgical techniques: Removal of stigma is very useful in sporophytic system. Pollen is directly dropped on to the ovules.
End-of-season pollination controversial technique.
High temperature: May induce pseudo fertility E.g. in Trifolium, Lycopersicon, Brassica, Oenothera exposure of pistils upto 60°C induces pseudo fertility.
Increased CO2 conc. in sporophytic system
High humidity
Salt, (NaCl) sprays are used by the Chinese
Irradiation: In a single locus gametophytic system. e.g. in solanaceae, acute irradiation with x-rays or γ-rays induces pseudo-fertility
Grafting
Double pollination
Other techniques like use of phytohormones, treatment of flowers with carbon-monoxide etc.

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