ABSTRACT
Interspecific incompatibility is a reproductive barrier resulting in failure of seed-set between two reproductively isolated species. Interspecific incompatibility prevents gene flow between species and maintains species identity. Prefertilization barriers prevent fertilization by arresting post-pollination events at one or many levels: pollen hydration, pollen germination, pollen tube entry into the stigma and pollen tube growth through the stigma and style. In most interspecific crosses, the arrest of post-pollination events seems to be passive as a result of lack of co-adaptation between the pollen and the pistil. All post-pollination steps require co-adaptation between the pollen and the pistil for successful completion of pollen-pistil interaction. Pollen adhesion and hydration depend on morphological and physiological co-adaptation between the pollen and the stigma. Pollen hydration is the result of water uptake from the stigma mediated through differences in the osmotic potential of the pollen and the stigma.
