Yeasts against grape pathogenic fungi: a sustainable alternative to agrochemicals

Biocontrol has become the promising approach in sustainable agriculture. This study explored the potential of epiphytic yeasts as natural antagonistic microorganisms for biocontrol. Yeasts isolated from Georgian Vitis vinifera (ssp. sylvestris and vinifera) were examined for their inhibitory activity against Botrytis cinerea, Aspergillus carbonarius, and Penicillium expansum. In vivo trials on infected berries and in vitro tests using dual-culture plate and double petri dish tests allowed the selection of 19 yeasts as potential biocontrol agents. Pichia kudriavzevii UMY 1470, Clavispora lusitaniae UMY 1471, Candida intermedia UMY 189, Cystofilobasidium infirmomiatum UMY 205 and Aureobasidium pullulans UMY 201 showed the best antagonistic activity in dual-culture plate assays. In double Petri dish tests, 100 % inhibition was observed using P. terricola UMY 197, P. kluyveri UMY 210 and Saccharomyces cerevisiae strains against the three pathogens, and P. kudriavzevii UMY 1470 against P. expansum and B. cinerea. Thus, the production of volatile organic compounds was verified by SPME/GC- mass spectrometry; S. cerevisiae UMY 1430 produced the most prominent inhibitory compounds (2- phenylethyl ester, oxalic acid, ethyl acetate, and heptanoic acid ethyl ester) against the three pathogens. The yeasts' tolerance to copper, a commercial fungicide, and sulphur dioxide was tested. C. intermedia UMY 189, A. pullulans UMY 201, Metschnikowia pulcherrima UMY 1472, and S. cerevisiae UMY 1423 were the most resistant yeasts to copper while P. kudriavzevii UMY 1470 and C. lusitaniae UMY 1471 were tolerant to the fungicide (up to 1 g/L). However, all yeast strains were sensitive to an oenological dose of sulphur dioxide. In conclusion, the inhibitory activity of the analysed yeasts proved to be promising; in field experiments will allow to fully examine their biocontrol potential.