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Physiology and Biochemistry

Phytotoxin Production by Diaporthe phaseolorum var. caulivora, the Causal Organism of Stem Canker of Soybean. B. Lalitha, Graduate research assistant, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803; J. P. Snow, and G. T. Berggren. Professor, and associate professor, respectively, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. Phytopathology 79:499-504. Accepted for publication 8 December 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-499.

Diaporthe phaseolorum var. caulivora isolated from soybean plants infected with stem canker produces a toxin that caused symptoms characteristic of stem canker when introduced into the plant. The amount of toxin and the degree of symptoms were linearly related. Four fungal isolates produced the toxin in culture in significantly different amounts, when measured in terms of the degree of symptoms and the dilution end point. The amount of toxin produced by the isolates correlated with the length of cankers produced by the fungus upon inoculation. Of the 12 plant species evaluated, only soybean and lima bean were sensitive to the toxin and also susceptible to the fungus. The purified toxin produced symptoms very similar to those of stem canker, and some of its chemical properties are similar to those of a phytotoxin suggested to have a role in pine wilt caused by Phomopsis sp. The D. p. caulivora toxin appears to play a role in stem canker of soybean.