Department of Plant Protection, College of Agriculture, Ferdowsi University of Mashhad, Iran.
To evaluate the effects of presence of insect pollinators on quantity and quality of seeds of two common cultivars of onion (Alliumcepa L.), namely Red Azar Shahr and Yellow Sweet Spanish, an experiment in a factorial randomized complete block design was carried out at two sites. Bulbs of equal size were planted with plant to plant 35 cm and row to row 50 cm spacing. At each site, experimental groups differed only in pollination method. About a week before flowering start, at each site 3 groups of 10 individual inflorescences as block replications of each treatment combination (pollination × cultivar) were selected randomly and marked. For each onion cultivar, half of the plants were left uncovered (free pollination), whereas the other ones were isolated from insect pollinators by using wooden cages covered with cloth net. When about 10 percent of black seeds were visibly exposed in the umbels, harvest was done. After drying, the number and weight of seeds produced per inflorescence as well as 1000 seed weight was measured for each treatment combination. Four weeks after the harvesting date the germination test of seeds produced in each treatment combination was evaluated. Non availability of insect pollinators during the flowering period of onion caused substantial reduction on seed number and seed weight per umbel. Also, seeds from free pollination flowers showed higher germination capacity than those isolated from insect visitors. However, varieties as well as experimental sites did not show significant influences on seed setting of onion.