The Microbial Community of Grape Berry

The microbial community of grape berry is composed of an array of species exhibiting differential physiological characteristics and relevance to vine growing and winemaking. The most important phytopathogens responsible for grapevine diseases worldwide are the oomycete Plasmopara viticola (downy mildew) and the ascomycete Erysiphe necator (powdery mildew). The causal agent of grey rot is the saprophytic mould Botrytis cinerea. A wide diversity of yeast species are also common contaminants of berry surfaces, but the key agent of wine fermentation, Saccharomyces cerevisiae, is rarely recovered from the grapes. Bacterial groups include the spoiling acetic acid bacteria and lactic acid bacteria responsible for the malolactic fermentation. These microorganisms colonise grape surfaces from berry set to ripening, following a repeatedly cyclic pattern year after year. Highly complex interactions and chemical signalling take place among grapevines themselves and with the intervening biota, which also include insects, birds and mammals. The fundamental role played by the nonmicrobial biota in grape berry microbiota ranges from their role (especially in the case of insects) as microbial vectors to the damage directly inflicted on the grapes, which pave the way to the entrance of the saprophytes. The precise biota and the resulting interactions depend fundamentally on the berry development stage, on the intactness of the grape skin and on the prevailing environmental conditions, and exert a profound effect on the fruit quality. Given the great ecological, technological and economical importance of studying the grape microbiota, it is somewhat surprising to find scarce and fragmented information available on these topics.

Here we provide a balanced, highly multidisciplinary overview of the most relevant components of grape berry microbiota. Our proposal establishes four distinct groups of microorganisms - residents, adventitious, invaders and opportunists - which are defined on the basis of grape biochemical evolution, nutrient availability and ability to proliferate on berry surface. Their natural proliferation is particularly dependent on two main events: veraison and berry damage. The origin and the colonisation sequence on berry surface by those several groups of microorganisms will be tentatively settled.

Keywords: Bacteria, Berry damage, Botrytis cinerea, Drosophila spp., Erysiphe necator, Grape berry microbiota, Oenococcus oeni, Ontogenic resistance, Plasmopara viticola, Saccharomyces cerevisiae, Skin integrity, Vectors, Volatile organic compounds, Yeast.