Characterization of antagonistic microorganisms against Aspergillus spp. from grapevine leaf and berry surfaces

This study aimed at controlling the common fungi causing postharvest Aspergillus rot of cv. Thompson seedless table grape (Vitis vinifera L.) via application of epiphytic biocontrol agents. Antagonistic yeasts and bacteria were isolated from the epiphytic flora associated with grape berries and leaves from five vineyards in Iran. A total of 130 yeast and bacterial isolates from grapevine surfaces were screened for antagonism against Aspergillus flavus, A. niger and A. ochraceus, the main species responsible for the accumulation of aflatoxin and ochratoxin A in grape berries. Seven yeast and bacterial isolates were selected based on their inhibitory effects on Aspergillus spp. and assayed by an in vitro nutritional competition test for their antagonistic capability. These isolates showed obvious antifungal activity against three different species of Aspergillus. Five yeast isolates were identified based on ITS region sequences as Candida membranifasciens (isolates Ka15 and Kh69) and Meyerozyma guilliermondii (Ka21, Kh59 and Kh60). Two bacterial isolates were identified based on the 16S rRNA gene sequences as Bacillus sp. (Ka3 and A10). Finally, the effect of antagonistic isolates on inoculated grape berries for their ability to inhibit infection by Aspergillus spp. was also investigated. All isolates showed antagonistic properties against the pathogens assayed at 25 °C and significantly reduced the disease progress on grape berries. Our data demonstrated that application of antagonistic microorganisms could be a promising alternative to fungicide treatments for controlling postharvest diseases of grapevine.