Pollen flow in the atmosphere of kiwi fruit (Actinidia deliciosa) orchards

Few studies have examined the atmospheric pollen flow of entomophilous plants. The rare works conducted with kiwifruit did not differentiate between pollen of staminate and pistillate flowers, and could therefore not assess the airborne pollen flow in terms of effective pollination. Our objective was to determine the atmospheric pollen flow in kiwifruit orchards over flowering and within a day. We used a passive pollen sampling technique followed by acetolysis, which enabled us to differentiate between pollen from staminate and pistillate flowers. The study was conducted in 3 orchards one year and a second year in one of these orchards. Large amounts of pollen from both staminate and pistillate flowers were airborne and maxima of over 5 millions fertile pollen grains per m and per day were captured in each study site. During daytime, most airborne pollen was recovered between 09.00 and 13.00 h for the two pollen types and this period was similar with that of anthesis and maximum insect foraging. Little wind pollination took place at night. Some airborne kiwifruit pollen was in clumps, even after the acetolysis treatment, particularly for the pollen of pistillate flowers. Overall, wind brought at most about 2200 fertile grains onto a surface equivalent to that of the stigmas of a pistillate flower during its receptive period. This figure is probably below the amount usually required to fertilize enough ovules to obtain a 100 g fruit.