The potential role of fungal volatile organic compounds in Aspergillus flavus biocontrol efficacy

Abstract

Pre-harvest application of inherently non-aflatoxigenic Aspergillus flavus strains is an effective biocontrol strategy to minimize aflatoxin contamination of agricultural commodities, but researchers still do not fully understand how A. flavus biocontrol strains establish control over aflatoxigenic fungi. In this in vitro study, we tested the potential for A. flavus volatile organic compounds (VOCs), identified from a previous study, to serve as regulators of mycotoxin production. We exposed four Aspergillus strains (one non-aflatoxigenic and three aflatoxigenic) to five VOCs unique to aflatoxigenic A. flavus, and five VOCs unique to non-aflatoxigenic A. flavus, to study their impacts on growth as well as production of two mycotoxins: aflatoxin and cyclopiazonic acid (CPA). We found that growth of the fungi was not severely impacted by VOCs. However, toxin production was greatly affected and highly variable between strains and VOCs. Two non-aflatoxigenic VOCs (3-octanone and trans-2-methyl-2-butenal) significantly reduced aflatoxins in all aflatoxigenic strains. Two other non-aflatoxigenic VOCs (2,3-dihydrofuran and decane) significantly reduced aflatoxin levels in all aflatoxigenic strains and each VOC completely inhibited CPA production in one aflatoxigenic strain. Our findings offer evidence that the mechanism of control implemented by biocontrol strains may involve chemosensing through the production of one or more VOCs. These findings can be used to identify natural selectable markers for improved biocontrol strains or to supplement current biocontrol efforts through post-harvest exposure to VOC-related chemicals that mimic the presence of biocontrol strains.