Influence of fungicide treatments on the occurrence of yeast flora associated with wine grapes

In this work, the effects of fungicide treatments on the distribution and presence of the yeast flora that colonise the surfaces of grapes were investigated. Samples were collected from three vineyards treated with different fungicide applications using two methodologies to detect the yeast flora. Our results show that organic fungicides applied on wine grapes during ripening cause a drastic reduction in the yeast flora. In the absence of fungicide treatments, Hanseniaspora uvarum was the dominant species, followed by Metschnikowia pulcherrima. Results of inorganic fungicide treatment trials confirmed the dominance of these wine fermenting yeasts together with a significant presence of Aureobasidium pullulans and Cryptococcus spp. The use of organic fungicides (in addition to inorganic fungicide application) showed A. pullulans as the predominant yeast species, followed by the Cryptococcus species, while wine fermenting yeasts were scarcely represented. The dominance of A. pullulans on grape surfaces treated with organic fungicides was confirmed in two consecutive vintages. In conclusion, organic fungicides directly applied on grape surfaces result in a dramatic reduction of yeast population and a shift in yeast populations towards A. pullulans.