SYNTHESIS AND BIOLOGICAL-ACTIVITY OF STEMTOXIN BY STEMPHYLIUM-BOTRYOSUM AND RELATED FUNGI

Ulocladium sp., Alternaria alternata f. sp. lycopersici, Stemphylium vesicarium and several isolates of Stemphylium botryosum were tested for their ability to produce polypeptides (M(r) = 26 900; 19 500; triplet at 15 500) similar to those associated with phytotoxicity of culture filtrates from S. botryosum pathogenic on alfalfa (Medicago sativa). Phytotoxic activity and groups of polypeptides with similar relative mobilities following sodium dodecyl sulfate-polyacrylamide gel electrophoresis were recovered in partially purified fractions from all Stemphylium isolates and Alternaria alternata f. sp. lycopersici, but not in similarly purified fractions from Ulocladium sp. Immunoglobulin G, produced in response to the denatured 26 900 polypeptide from S. botryosum Mu9 phytotoxin (stemtoxin), cross-reacted with similar polypeptides from all Stemphylium isolates and A. alternata f. sp. lycopersici. Ability to produce stemtoxin in vitro together with ability to penetrate alfalfa leaves in vivo was not sufficient for pathogenicity of Stemphylium on alfalfa.