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Physiology and Biochemistry

Phytotoxic Substances Produced by Some Isolates of Cercospora arachidicola Are Not Cercosporin. S. A. Fore, Research assistant, North Carolina State University, Raleigh 27695-7616; M. E. Daub, and M. K. Beute. Assistant professor, and Professor of plant pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 78:1082-1086. Accepted for publication 12 April 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1082.

Cercosporin is a red-colored, light-activated toxin produced by Cercospora species. It has been isolated from fungal cultures and from infected leaf tissue of several hosts at levels of 1–10 μg/g of lesions or infected leaf tissue. We investigated the production of cercosporin by C. arachidicola, causal agent of peanut early leaf spot. No evidence was obtained for cercosporin production in vivo or in vitro by C. arachidicola. At an approximate detection limit of 12 pmoles of cercosporin/sample, cercosporin was not found in infected peanut leaves or lesions. Our procedures allowed extraction and detection of cercosporin concentrations below those that cause visible symptoms when purified cercosporin is injected into peanut leaves. Although the four isolates of C. arachidicola used for in vitro studies produced a red pigment in culture, this pigment was not cercosporin. Two major compounds with absorption maxima at 465 and 435 nm could be separated by thin-layer chromatography from extracts of cultures of four isolates of C. arachidicola. Crude culture extracts and both compounds of C. arachidicola were phytotoxic and exhibited antimicrobial activity in both the light and the dark. These compounds could not be detected in infected tissue. The identity and possible role of the phytotoxic substances isolated from C. arachidicola are not known.