Yeast diversity on grapes from Galicia, NW Spain: biogeographical patterns and the influence of the farming system:

Aim: Organic viticulture has increased in recent decades, worldwide. Farming system influences grapes’ yeast populations and, therefore, fermentation dynamics and wine quality. This work aims to study yeast diversity on grapes and musts from organic and conventional production in different areas within Galicia (NW Spain) and to evaluate the existence of yeast geographic patterns (microbial terroir) in this region.Methods and results: During the 2015 vintage, 42 grape samples were collected from four Denominations of Origin (DOs) in Galicia. Representative cultivable yeasts from grapes and must samples were isolated and characterised at the species level in the Estacion de Viticultura e Enoloxia de Galicia (EVEGA-AGACAL). Results were compared among DOs and between organic and conventional production. A total of 33 yeast species were identified. Organic production showed27.3% higher species richness than conventional production. Accordingly, diversity indexes (H′ and E) were higher under organic cultures compared to conventional production. The highest yeast diversity was found in Rias Baixas and Ribeira Sacra DOs. The predominant yeasts were Aureobasidium spp., Metschnikowia spp., Hanseniaspora uvarum and Cryptococcus spp., although their proportion varied depending on the farming system and location. Furthermore, important differences were observed in minor species, which appeared mainly in organic cultivation. In addition, a biogeographic pattern was found: Issatchenkia terricola and Starmerella bacillaris were isolated in Rias Baixas and Ribeira Sacra DOs, whereas Lachancea thermotolerans was ligated to Monterrei and Ribeiro DOs. ANOSIM, PERMANOVA and PCA analysis confirmed this differentiation.Conclusions: The results indicated that an organic farming system favoured yeast diversity on grapes and musts. Moreover, species distribution made it possible to establish a biogeographic pattern in the yeast population that could be associated to a particular microbial terroir and wine typicality.Significance and impact of the study: This study reports for the first time a survey on yeast diversity on grapes and musts from organic and conventional production in different areas within Galicia. The results highlighted the role of organic culture as a tool to preserve yeast richness and the existence of biogeographic patterns of yeast communities in vineyards in NW Spain, which could contribute to wine typicality of specific areas.