The vineyard ecosystem as a dynamic reservoir of Saccharomyces yeasts biodiversity

GONZALEZ M.L.; LERENA M.C.; ROJO M.C.; CIKLIC I.; COMBINA M.; MERCADO L.

Bento Gonzalves

Congreso; 39º Congresso Mundial de la Viña y el Vino; 2016

Organizacion Internacional de la Vid y el Vino (OIV)

Yeasts have a key role in the alcoholic fermentation of wine as well as in contributing to the sensory characteristics of the final product. They also integrate the microbial communities present in the vineyard. Grape production and winemaking are activities of large tradition and great economic impact in Mendoza, Argentina, therefore, to encourage its development is essential. In this sense, all over the wine world, microbiological tools are applied as valuable strategies for wine diversification and adding value. Furthermore, the knowledge of the phenomena determining the presence of different strains of Saccharomyces cerevisiae, the most important wine yeast, in the vineyards of a grapegrowing region, is the fundamental starting point. The aim of this study was to determine the presence of S. cerevisiae populations in different niches (plant and soil) of the vineyard, and to analyze the persistence of them along four stages of the annual growth cycle of grapevines (harvest and post-harvest, dormancy, budburst and veraison). The study took place in a Malbec vineyard located in the Zona Alta del Río Mendoza winegrowing area. Through a systematic sampling, 10 sectors of the vineyard plot were selected and samples of soil and of parts of the plant (grapes, bark, buds and flowers) available at each stage were obtained. Grapes were harvested and winemaking was carried out in an experimental winery, monitoring yeast populations in different stages of the fermentation. In parallel, two samples of water used for surface irrigation of the vineyard, were analyzed. All samples were enriched and then S. cerevisiae yeasts were isolated and intraspecific characterization by their PCR interdelta patterns was performed. A variation was observed in S. cerevisiae populations at different stages of the phenological cycle studied, being different in each case the niche (soil, bud, bark, flower, grape) from which these yeasts could be isolated. For example, S. cerevisiae could be detected in the soil only in one sector of the plot in the post-harvest stage and exhibiting low strain molecular diversity. The veraison grapes showed little presence of S. cerevisiae yeast and very low diversity of strains. This fact is in striking contrast to the results obtained in the mature grapes, where the greatest number and variability of S. cerevisiae isolates were observed. Irrigation water showed high diversity of S. cerevisiae yeasts, but these strains could not be isolated in other niches. In spite of this, it is important to appreciate the water as a possible mean of spread of yeast in the vineyard. During the fermentation carried out following the protocol of red winemaking, a very limited polymorphism was observed, with the presence of few different PCR-interdelta patterns and persistence of them in different stages of the process. On the other hand, a commercial strain was also detected in this vineyard, necessarily coming from some cellar, it indicates a spread or flow of yeasts from there through mechanisms that should be studied. The presence of this commercial strain was exclusive at three vineyard sectors: it was isolated from samples of ripe grapes of two sites, and after eight months (in budburst stage), it was found in the buds of another sector. According to the results, the vineyard is a dynamic genetic reservoir of yeasts. This study contributes to a better understanding of the biodiversity of native yeasts of Argentinean vineyards and to the preservation of regional interest genetic resources, enabling future development of native inoculums that will contribute to improve the quality of Argentinean wines and the best expression of terroir in wines from Mendoza.