Effects of water activity (aw) on the growth of some epiphytic micro-organisms isolated from grape berry

It is well known that wet weather often induces microbial deterioration of grape berries by Botrytis cinevea during the noble rot process, and that heavy rainfall increases the number of epiphytic micro-organisms. To better understand the influence of environmental conditions, we investigated the effects of water availabilty on the in vitro growth of 7 yeast strains, 10 strains of bacteria and one strain of the fungus Botrytis cinerea, isolated from grape berries. The results confirm that growth of Botrytis cinerea is inhibited at water activities (a(w)) < 0.93. Growth was highest if sucrose was added to the medium compared to other solutes (KCl, CaCl2), Most bacteria were more sensitive to water deficit than Botrytis cinerea. Bacteria were only able to grow at a, ranging from 0.997 to 0.940. Yeasts were more resistant than bacteria. Most yeasts grow at aw between 0.96 and 0.88, The present results may contribute to control epiphytic micro-organisms in over-ripened fruit of grapevine.