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How does self-incompatibility prevent self-fertilization in flowering plants?

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Bumblebee on teasel — plant reproductive system A large bumblebee (*Bombus* species) pollinating a teasel flower head (*Dipsacus* species).

Self-incompatibility is a genetically controlled mechanism that prevents self-fertilization in many flowering plants. Unlike structural or temporal barriers, this process relies on chemical substances within the plant to inhibit the reproductive success of its own pollen.12

When self-incompatibility occurs, it typically manifests in one of two ways:
* The pollen fails to grow or germinate on the stigma of the same flower that produced it.12
* After germination, the pollen tube fails to grow normally down the style, preventing it from reaching the ovule to effect fertilization.12

This process is not always absolute and can vary in intensity throughout the flowering season. It is commonly found in species such as cabbage and white clover, and it is generally absent in plants that already possess strong structural or temporal barriers to self-pollination, as the evolution of a single effective mechanism is typically sufficient for a species' reproductive needs.12