(474) A Selected Yeast for Control of Aspergillus flavus in Pistachio Orchards

Abstract

Aspergillus flavus produces aflatoxin, a cancer-causing contaminant of pistachio in many production areas. A superior yeast strain of Pichia anomala has been demonstrated to inhibit the growth of A. flavus in the laboratory. It was selected for further study and potential release based on tests of durability and ability to inhibit A. flavus growth. This strain has been tested in the field for the past two years to evaluate its ability to survive in a field environment and to inhibit A. flavus production. The yeast was evaluated in the field to determine if: 1) the biocontrol yeast can survive in pistachio orchards; 2) the yeast has no phytotoxic effects on the pistachio trees or nuts; and 3) the yeast can be demonstrated to control A. flavus in the field. Studies during 2003 were conducted using a replicated experiment with three yeast concentrations and a water control. Treatments applied later in the season were found to be most effective. Highest yeast concentrations were observed just prior to harvest. Three spray concentrations and a water control were applied to evaluate possible phytotoxic effects on pistachio during 2004. No differences in leaf or nut appearance, in nut percent splits, or dry weight were observed for any of the treatments when compared to the water control. Artificial wounding experiments were also conducted during 2003 and 2004 to simulate the occurrence of early split nuts, the primary repository for A. flavus contamination. A 5× reduction in A. flavus colonization was observed on treated wounded nuts vs. untreated wounded nuts. A 5× reduction in A. flavus sporulation was also observed on treated wounded nuts vs. untreated wounded nuts.