(Gray mold)

Long perceived as a secondary disease, gray rot is now considered in France, and rightly so, as the main problem with ripe grapes. It is omnipresent in French vineyards, and more particularly in Burgundy and Beaujolais, as well as in the Loire Valley ( see link ).

Note that botrytised clusters harbor on the surface or in the heart of other fungi, several Penicillium spp., Aspergillus spp., Trichothecium roseum forming complexes whose repercussions on the quality of the harvest and the wines can be catastrophic.

The biological variability of Botrytis cinerea , responsible for gray rot, is still poorly understood. Some phenotypic differences were observed between strains, concerning the appearance of their mycelial colonies in vitro (Figure 1), their aggressiveness or even their virulence. But it is above all in terms of their sensitivity to fungicides that the situation is most contrasted between strains. Indeed, resistance phenomena to one or more fungicides have been reported in many countries.

Figure 1

Rather recent molecular biology work has revealed great genetic variability within the species Botrytis cinerea . This fungus is in fact a complex of species that can be divided into at least two groups.

The I group or subpopulation pseudo-cinerea is distinguished by its resistance to fungicidal fenhexamid and has one of two alleles of the gene Bc-hch vegetative incompatibility. The Group II consists of stem called " vacuma " and " transposed ". The subpopulation transposa transposons has two active in its genome, Boty and Flipper whereas these two transposons are absent or inactive in the vacuma subpopulations and pseudo-cinerea . It would appear that the subpopulation B. transposa is better adapted to grapevine infection.

Classification : Fungi, Ascomycota, Leotiomycetes, Leotiomycetidae, Helotiales, Sclerotiniaceae
Téléomorphe : Botryotinia
English name : gray mold