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Physiology and Biochemistry

Production and Nature of a Host-Specific Toxin from Alternaria alternata f. sp. lycopersici. D. G. Gilchrist, Department of Plant Pathology, University of California, Davis, CA 95616; R. G. Grogan, Department of Plant Pathology, University of California, Davis, CA 95616. Phytopathology 66:165-171. Accepted for publication 19 August 1975. DOI: 10.1094/Phyto-66-165.

Cell-free culture filtrates from isolates of Alternaria alternata f. sp. lycopersici pathogenic to certain cultivars of tomato contained a toxin which elicited foliar symptoms characteristic of the stem canker disease on naturally infected tomatoes. Tomato cultivars, resistant to the pathogen were at least 1,000-fold less sensitive to the toxin than susceptible cultivars. Nonpathogenic A. alternata isolates did not produce bioassayable toxin when grown in standing liquid culture. Of representatives from nine families tested, only tomato was susceptible to the pathogen and the toxin. Resistance to the pathogen in tomato is inherited as a single gene expressing complete dominance, while sensitivity to the toxin is controlled by a single locus with two alleles expressing incomplete dominance when heterozygous. The toxin is a highly stable, low-molecular-weight, cationic molecule, which based upon ion exchange, gel filtration, and paper chromatographic behavior, is produced in culture as a single molecular species. Furthermore, based upon its host-specific nature and chemical properties, the toxin has not been reported heretofore as a phytotoxin produced by Alternaria spp.