Associated microorganisms
to acid rot

A complex of yeasts and acetic bacteria 

This complex seems to fluctuate depending on the production areas affected around the world. In France, various microorganisms have been linked to this rot of grape berries:

• of yeast : Kloeckera apiculata * (Reess) Janke (or its teleomorph Hanseniaspora uvarum (Niehaus) Shehata * Mrak & Phaff) * Candida stellata (Kroemer & Krumbholz) SA Mey. & Yarrow **, Pichia membranifaciens (EC Hansen) EC Hansen ***, Metschnikowia pulcherrima Pitt & MW Mill., Rhodotorula spp., Candida krusei (Castell.) Berkhout **, Zygosaccharomyces rouxii (Boutroux) Yarrow *. The list of yeasts is not exhaustive, many other genera and species have been isolated from rotten berries elsewhere in the world. Note that Kloeckera apiculata is one of the most common yeasts in grape berries in the world.
• of acetic acid bacteria : several Gluconobacter spp. Asai 1935 (frequent), Acetobacter aceti (Pasteur 1864) Beijerinck 1898, Acetobacter pasteurianus (Hansen 1879) Beijerinck and Folpmers 1916 (rarer). Here again, other species have been isolated from berries affected by acid rot in other production regions outside mainland France. Note that Acetobacter spp. would be the dominant acetic bacteria in the final stage of the development of acid rot on grape berries.

They should be aware that the rotten acid clusters generally do not allow other microorganisms infested with the grape berry to develop, the acetic acid produced (acting either by contact or by vapor effect) inhibiting the germination of their spores and their growth. mycelial.

Classification : *Saccharomycodaceae, Saccharomycetales, Saccharomycetidae, Saccharomycetes, Ascomycota, Fungi ; **Incertae sedis, Saccharomycetales, Saccharomycetidae, Saccharomycetes, Ascomycota, Fungi ; ***Pichiaceae, Saccharomycetales, Saccharomycetidae, Saccharomycetes, Ascomycota, Fungi ; ****Metschnikowiaceae, Saccharomycetales, Saccharomycetidae, Saccharomycetes, Ascomycota, Fungi.

Various potential vectors, in particular Drosophila

High populations of Drosophila ( Drosophila melanogaster and Drosophila simulans ) are generally observed in plots affected by acid rot (Figure 1). The spatio-temporal evolution of this disease probably results from complex interactions between the microorganisms involved and these potentially vector insects.

Let us add that for several years a new fruit fly has been found in the vineyard: Drosophila suzukii . the latter, reported for the first time in the vineyards of the South-West since 2014, would be much more damaging than the previous ones because of the possibility that it has to infest uninjured berries before maturity thanks to its formidable piercing ovipositor and heartbreaking difficulty in the cuticle. 

Knowledge of acid rot, known as “ sour rot ” by the Anglo-Saxons, was quite limited. Rather sporadic disease and dependent on the rather white grape varieties, it is favored by the overripe of the berry. Its etiology has only been considered very occasionally, particularly in Italy and France, and more recently in Portugal, etc.