Sources and Assembly of Microbial Communities in Vineyards as a Functional Component of Winegrowing

Abstract

Microbiomes are integral to viticulture and winemaking - collectively termed winegrowing - where diverse fungi and bacteria can exert positive and negative effects on grape health and wine quality. Wine is a fermented natural product, and the vineyard serves as a key point of entry for quality-modulating microbiota, particularly in wine fermentations that are conducted without the addition of exogenous yeasts. Thus, the sources and persistence of wine-relevant microbiota in vineyards critically impact its quality. Site-specific variations in microbiota within and between vineyards may contribute to regional wine characteristics. This includes distinctions in microbiomes and microbiota at the strain level, which can contribute to wine flavor and aroma, supporting the role of microbes in the accepted notion of terroir as a biological phenomenon. Little is known about the factors driving microbial biodiversity within and between vineyards, or those that influence annual assembly of the fruit microbiome. Fruit is a seasonally ephemeral, yet annually recurrent product of vineyards, and as such, understanding the sources of microbiota in vineyards is critical to the assessment of whether or not microbial terroir persists with inter-annual stability, and is a key factor in regional wine character, as stable as the geographic distances between vineyards. This review examines the potential sources and vectors of microbiota within vineyards, general rules governing plant microbiome assembly, and how these factors combine to influence plant-microbe interactions relevant to winemaking.

Keywords: biogeography; metagenomics; microbial dispersal; microbial ecology; microbiome; terroir; viticulture.

Figure 1

Spatial and temporal variation in vineyard microbiomes is shaped continuously by a mosaic of biotic and abiotic factors. Climate and weather patterns drive cyclical phenotypical stages of grapevines and their resident microbiota, spatial heterogeneity, and abiotic mixing/exchange of microbiota year-round (see also Figure 2). Several potential reservoirs (e.g., soil, grapevine bark, and other nearby plants) serve as overwintering sites for grapevine fungi and bacteria. Humans, insects, and weather events induce microbial transmission, particularly during the growing season (spring, summer, and autumn). Plant genotype continuously selects microbiota from this local pool.

Figure 2

The vineyard is an interconnected and open ecosystem that exchanges microbiota at intra-vine, intra-vineyard, local, and regional scales. Microbiota are naturally exchanged between the regional, local, and intra-vineyard scale by wind/weather factors, and locally by human activity, insects, and other factors. At the intra-vineyard and intra-vine scales, microbes are exchanged between vines and plant compartments (grapes, phyllosphere, and rhizosphere/soil) by various vectors, including wind, rain, insects, and human activity. These transmission pathways are subject to dispersal limitation, shaping the local pool of available microbiota. Environmental factors and plant genotype exert further selective pressures to shape the microbiota of different plant compartments.