Enhancement of pollen germination by promotive factors in incompatible pollen

Cultivated and wild almonds are self-incompatible and thus require outcross ing by insect pollinators to produce viable seed. In commercial production, considerable efforts are directed towards placement and selection of culti vars for cross-pollination. However, since honeybees do not distinguish bet ween the different cultivars, stigmas are usually covered by a mixture of b oth compatible and incompatible pollen. Using in vitro assays, we demonstra ted that pollen extracts promoted germination in self pollen with no inhibi tory effects observed. Elemental analyses of pollen extracts showed that en hanced levels of Ca, Mg, K, Na, and P were eluted from the grains. From thi s, we raise the question of possible interaction between compatible and inc ompatible pollen, and speculate that incompatible pollen grains may support and enhance germination of adjacent compatible pollen.