Q.What is self-incompatibility? Briefly explain why self-pollination fails to produce seeds in a self-incompatible plant.

Self-incompatibility is a genetic, physiological mechanism, common in families such as Brassicaceae and Solanaceae, that prevents self-pollen (or pollen from a genetically similar individual) from bringing about fertilisation, even when the pollen has successfully landed on the stigma of a compatible flower.

Self-pollination does not lead to seed formation in a self-incompatible plant because the pistil is biochemically able to recognise the pollen as 'self' and actively blocks its progress -- most commonly by preventing the self-pollen grain from germinating on the stigma at all, or, if it does germinate, by arresting the growth of its pollen tube somewhere within the style before it can reach an ovule. Since the male gametes never reach the embryo sac, syngamy and triple fusion cannot occur, and no seed is formed -- even tho …

Define self-incompatibility as a recognition-and-rejection system, then explain WHERE it acts (germination on stigma …

Confusing self-incompatibility with a structural barrier like herkogamy -- self-incompatibility acts even when self-pollen physically reaches th …