Effects of supplementary pollination on cropping success and fruit quality in pistachio

The effects of pollen supplementation in pistachio orchards using an electrostatic pollination device were investigated in a 3-year study (1996-98) in San Joaquin Valley, California, USA. Both yield and fruit quality (per cent split fruit) were tested in several experiments. Applying smaller amounts of pollen (1.5 g per tree in early application only in 1996 or 0.5 g in two applications in 1997) resulted in higher yields than with open pollination or supplementary pollination using larger amounts of pollen (1.5 g per tree in four applications in 1996 or 1.0 g in two applications in 1997). Applying 1.0 g pollen in two applications in 1998 resulted in decreased yields compared with open pollination or non-electrostatic pollination. Pollen germinability on the stigma was greatest for open pollination suggesting that overloading the stigmas with pollen in supplementary pollination may not only reduce yield but also increase competition between pollen grains. The per cent split fruit significantly increased only once in 1996. When pollination is a limiting factor, electrostatic pollination of pistachio can increase yield and may even increase fruit quality. However, when pollination is not a limiting factor, electrostatic pollination may even reduce yield.