Influence of Resveratrol on Germination of Conidia and Mycelial Growth of <i>Botrytis cinerea</i> and <i>Phomopsis viticola</i>

Abstract

Abstract After inoculation of agar substrates containing resveratorl (an inducible stilbene characteristic for Vitaceae) with low concentrations (500/cm 2 ) of Botrytis spores, developing germ tubes showed malformations and growth stopped. High, density inoculations (10,000/cm 2 ) resulted in apparently normal growth, but stress conditions were indicated by the formation of a large number of sclerotia after 14 days. By contrast, growth of Botrytis and Phomopsis colonies starting from pieces of mycelium was slowed down by resveratrol concentrations 50 ppm and stopped by higher concentrations. More than 500 ppm (suspensions) induced rhythmical growth; at the front of the mycelium a clear zone appeared, which was free fromstilbene crystals but exhibited a brownish pigmentation. In liquid cultures pigmentation but no growth inhibition was observed. It is assumed that resveratrol is oxidized by fungal laccases whose isoenzyme bands can be stained with resveratrol after isoelectric focusing. The different effects of this substrate on fungal growth in liquid and on solid media is explained by the localized action of laccases on solid substances where the radius of diffusion is limited.