Factors affecting the nectar production and pollination of hybrid onion (Allium cepa L.)

Successful pollination of hybrid onion (Allium cepa L.) flowers greatly depends on adequate nectar production. In order to understand both the physiology of onion nectar production and its influence on onion pollination, a series of experiments were performed. Nectar was collected from onion flowers during a 24-hour period. These nectar samples were compared to the daily environmental conditions. Production patterns showed mid- to late-morning peaks and late evening peaks. Nectar appeared to be reabsorbed by the flowers in the afternoon. Relative humidity was inversely related to nectar production while temperature was positively related.; The nectar production of hybrid onion also was compared to that of hybrid carrot and alfalfa. Carrot produced significantly more nectar than onion or alfalfa and attracted more honey bees than the other two crops.; In order to better understand the physiological dynamics of onion nectar production, hybrid onions with varying bulb characteristics were planted and subsequent nectar production measured. Bulb weight, bulb diameter, and leaf characteristics had no effect on nectar production. Higher mono- and disaccharide concentrations had a positive effect on nectar production. Plants covered with a shade cloth for 3 days produced a greater amount of nectar than control plants, suggesting that stored carbohydrate from onion bulbs may be the source of carbohydrate for nectar production.; In order to attract more pollinators to the onion seed production field, honey bees were conditioned to associated onion floral odor with a reward. Isolated nucleus hive were fed 30% sucrose solutions scented with 0.2% solution of onion floral odor compounds. After feeding upon these compounds for six weeks, the treated hives did not visit the onion fields more frequently than the control hives.; The surface of the onion flower nectary was examined using scanning electron microscopy. Modified stomata were found scattered at the base of the junction of the carpels.; These studies emphasize the importance of selective breeding and screening for high nectar producing onion lines in order to insure adequate subsequent nectar productions. Future studies should focus on understanding the mechanism of partitioning within the plant to increase the production of nectar.