Tolerance of Yeast Antagonists Isolated from Pistachios in Environmental Stresses

Aflatoxins are the most contaminant of various agricultural products, especially pistachios. Nowadays, biological control is one of the successful methods in aflatoxin mitigation. Yeasts can be used as a safe and efficient strategy to mitigate aflatoxin in pistachio. The present study screens the high tolerant yeast isolates to environmental stresses.

Soil and pistachio nut samples were collected from commercial pistachio orchards. A dilution series method and GPYA medium were used to isolate yeast species. The ability of yeast isolates to inhibit the growth of Aspergillus flavus was investigated through dual culture, volatile compound, and non-volatile compound assays. The ammonia vapor method was used to evaluate the effectiveness of yeast isolates on aflatoxin production in cultural assays. The tolerance of isolates to non-living stresses was measured in optical density (OD) using spectrophotometry assays at 600 nm in a TSB medium.

The highest inhibitions of mycelial growth in volatile and non-volatile compounds, as well as dual culture, belonged to 78-3-2, YP4-11, 58-15, and 47-8 isolates by 79%, 88%, and 75%, respectively. The highest tolerance to salinity, drought, and heat stresses in the TSB medium was measured for 9, 6-5, and 181yeast isolates by 1.84, 0.75, and 2.18 (OD), respectively.

Selected isolates can be suitable candidates for field testing after further assays and accurate identification.