Question

What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

Answer 1

Hint: Inbreeding in flowering plants is avoided by self-incompatibility. In order to sustain the species' health and survival, genetic diversity is necessary. Human beings also unintentionally minimize genetic diversity in domesticated crops and animals by choosing their traits of interest.

Complete answer: Self-incompatibility is a genetic process in which pollen germination of pollen tube development in the pistil is prevented from fertilizing the ovule. Self-pollination, owing to the relationship between pollen chemicals and stigma, does not contribute to seed formation in self-incompatible plants. The lack of male and female gamete fusion results in no seed formation in these plants. The self-incompatibility mechanism (SI) avoids self-fertilization and thus, facilitates outcross and allogamy that should not be confused with physical or temporal genetically regulated mechanisms (preventing self-pollination), such as heterostyled and sequential hermaphroditism (dichogamy). In SI plants, the process of pollen germination, pollen tube formation, ovule fertilisation and embryo production is stopped at one of its stages when the pollen grain formed in a plant, a matching allele or genotype reaches the stigma of the same plant or other plants, and then no seeds are produced.
In-plant breeding, self-incompatibility is a very significant process, it has a profound impact on approaches and goals of plant breeding.
(1) Self-incompatibility is used in the development of hybrid seeds. For that it is appropriate to interpolate two self-incompatible but cross-compatible lines; a hybrid seed will be seeds obtained from both lines.
(2) Self-incompatibility offers a way for hybrid seed development without emasculation and without resorting to genetic or cytoplasmic male sterility.
(3) The self-incompatibility mechanism, which is not possible in self-compatible plants, enables the combination of desirable genes in a single genotype from two or more separate sources by natural cross-pollination.
(4) In the case of pineapple, commercial clones are self-incompatible, resulting in the production and seedlessness of their fruits.

Note: The method of self-incompatibility includes the identification of the pistil cells of self-related pollen, which is accompanied by the rejection of the incompatible pollen.