Pollination biology of the tree jujube (Ziziphus jujube) in Hanoi, Vietnam

The floral and pollination biology of three sweet varieties of the tree fruit jujube were studied in orchards in Hanoi, Vietnam during September and October, 2010. Longevity of a single flower was approximately 1-1.5 days. In the three varieties studied, anthesis occurred from 12:00 to 13.00h and had three distinct phases: 1) asexual phase lasting 1-2 h; 2) male phase lasting approx. 2.5 h, pollen became accessible when the anthers dehisced at around 16:00h; and 3) female phase lasting 20+ h. The stigma was strongly receptive on the 2nd day of anthesis. Jujube produces a small amount of nectar (1.47µl - 3.70 µl) at the base of the flowers at different times of day and sugar concentration is quite variable (12% - 65%). Apis species (Apis cerana , Apis florea) represented 76% of floral visitors. Other floral insect visitors included primarily Dipterans. Honey bees visited high outer branches more often than low outer and inner branches; this was not true for non-Apis species. Experiments involving bagging of blossoms, showed the greatest fruit set occurred with natural pollination (open flowers, 5.6%) and natural pollination in daytime (bagged at night, 5.5%). Self-pollination achieved lower fruit set (4.1%). Natural pollination at night (bagged during daytime) and wind pollination (continuously bagged) yielded the lowest fruit set (2.9% and 2.6%, respectively). Insects, especially A. cerana and A. florea , play an important role in jujube fruit set.