2018 ASHS Annual Conference

Substantial dust generated by flail mowers in California’s Central Valley pistachio (Pistacia vera L.) orchards led to the hypothesis that field dust disrupts pollination and fruit set in pistachio. In spring, clusters with flowers at the green tip stage were bagged and hand-pollinated with pollen:dust mixtures at the different ratios on five successive days. The stigmatic structure, the rates of viable pollen, fruit set, nut drop, blank and nut split were all investigated as factors involved in the progress of pollen-stigma interactions. This study also evaluated the effect of herbicide residues in dust to both pollen viability and pistil morphological structure. The gibberellic acid (GA) concentration in the florets of the pollen and dust trials, and the bagged control was tested. In 2016 and 2017 both pollen viability and stigma quality were damaged by dust, resulting in a poor crop yield via decreased fruit set, increased parthenocarpy and a lower proportion of split nuts. The stigmatic surface were wilted and distorted following the dust contamination. The papillae cells disappeared in the toxic 1:1 trial. The GA₃ content in flowers of both the pollen and dust treatments was higher than in the non-pollinated flowers, which suggested dust could stimulate the parthenocarpy of pistachio, and therefor nut blanking.