Grapes and Vineyard Soils as Sources of Microorganisms for Biological Control ofBotrytis cinerea

Abstract

In the search for biological agents capable of controlling the phytopathogenic fungus <i>Botrytis cinerea</i>, winegrape cuticles of several <i>Vitis vinifera</i> varieties and different soils from Uruguayan vineyards were screened for microorganisms that could be antagonistic to the fungus. Among 223 isolates of yeasts and bacteria, eight non-<i>Saccharomyces</i> yeast strains and four bacteria showed greater than 50% effectiveness in vitro against <i>Botrytis cinerea</i> compared with the growth of the control. A species of <i>Bacillus</i> (isolate UYBC38) and an isolate of the yeast <i>Hanseniaspora uvarum</i> (isolate UYNS13) showed high in vitro antagonistic capability against the pathogen; both organisms were very effective (100% and 90%, respectively) in controlling rot development on grape clusters. These two isolates were selected for further laboratory and vineyard studies. In order to prevent fermentation problems, both strains were tested against the wine yeast M522 and other natural non-<i>Saccharomyces</i> strains before field trials were conducted. The possible mechanisms of antagonism against <i>B. cinerea</i> were studied. Yeast strain UYNS13 showed only competition for nutrients. Although the <i>Bacillus</i> sp. strain consumed significantly more nitrogen from grape juice than <i>B. cinerea</i>, the relevant mechanism of antagonism of this bacterium was the production of anti-fungal substances. These compounds completely inhibited germination of <i>B. cinerea</i> conidia in vitro by disrupting the conidial cell wall, resulting in leakage of protoplasm. Applications of UYBC38 in the vineyard showed that this strain could survive on leaves and fruits for 45 to 70 days after spraying. The strategy of increasing the natural antagonistic population present in vineyards to prevent fungal diseases is discussed as low-input viticulture.