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How does self-incompatibility prevent some plants from pollinating themselves?

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Close-up of triticale grains scattered on a wooden surface with several wheat-like triticale heads lying on top. — Plant breeding Triticale is a hybrid of rye and wheat.

Self-incompatibility is a genetically controlled mechanism that prevents self-fertilization in many plants with perfect flowers, which contain both stamens and pistils.12

In this process, pollen from the same plant—or from another plant with an identical genetic constitution—is unable to successfully fertilize the flower. This occurs because the pollen fails to germinate on the stigma, or, if it does germinate, the pollen tube fails to grow normally down the style to reach the ovule. Consequently, fertilization cannot take place.13

This system serves as a device to encourage cross-pollination, ensuring that the plant receives pollen from a different individual rather than relying on its own. Examples of self-incompatible plants include sweet cherries, plums, apples, pears, tobacco, cabbage, and white clover.21