GROWTH-KINETICS OF BOTRYTIS-CINEREA ON ORGANIC-ACIDS AND SUGARS IN RELATION TO COLONIZATION OF GRAPE BERRIES

The relationship between hyphal growth and branching of the grape path ogen Botrytis cinerea was determined on solid media containing either glucose, fructose, sucrose, tartaric acid or malic acid. The concentra tion of the carbon source had little effect on specific growth rate or the specific rate of tip formation, but growth was inhibited at high concentrations of tartaric and malic adds. Hyphal growth unit length a nd hyphal extension rate increased with increasing sugar concentration and were always significantly greater than values on tartaric or mali c acids. The data provide an explanation for colonization patterns of grape berries. Growth will be poor during the period from setting to t he onset of ripening, when organic acids are the main carbon source pr oduced by the berry. Following the onset of ripening, the production o f sugars provides more favourable carbon sources for the fungus, enabl ing achievement of higher specific growth rates, greater hyphal extens ion rates and, hence, greater colonizing potential.