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.
