Seed development

Onion seed set and development are markedly affected by a number of factors, the most important ones being growth conditions, availability of pollinating insects, and the genetic make up of the individual plant. Cross-pollination is predominant in onions and leeks, in chives and most probably also in other alliums. However, onions are self-compatible, and regardless of earlier accounts, protandry does not prevent their self-pollination. In onions, pollen shed begins at anthesis and continues at irregular intervals for the next 24 to 36 h and may last up to 2 d. High temperatures and air humidities below 70% accelerate the process. Twelve to twenty four hours after pollination, the first pollen tubes with two sperm-nuclei, enter the micropyle. Onion seeds are produced in a wide range of environments, and weather conditions may change considerably during seed growth and ripening on the mother plant. These influence seed composition and subsequent performance.