Biotransformation of the phytoalexin camalexin by the phytopathogen Rhizoctonia solani

The unusual metabolism of the cruciferous phytoalexin camalexin by virulent and weakly virulent isolates of the root rot fungus Rhizoctonia solani Kuh n is reported. This biotransformation proceeded via 5-hydroxycamalexin, whi ch was further biotransformed into more polar metabolites. Importantly, the metabolites resulting from transformation of camalexin were significantly less toxic to the pathogen than camalexin. Thus, it was concluded that R. s olani can detoxify camalexin through oxidation of the indole ring. The chem istry involved in the structure determination of the intermediates of this pathway, their synthesis as well as antifungal activity is described. (C) 2 000 Elsevier Science Ltd. All rights reserved.