Biological Activity and Specificity of a Toxin Produced byCladosporium fulvum

Abstract

The biological activity of a glycoprotein toxin produced in vitro by C. fulvum was studied by necrosis, callose deposition and ion leakage assays. Concurrent appearance of callose and necrosis was not altered by the toxin''s degree of purification or concentration. Increased leakage of electrolytes from toxin-treated tomato leaf tissue was concentration-dependent, and this assay was the most sensitive. As judged by necrosis and callose deposition, C. fulvum toxin from races 1, 10 and 12 had similar effects on all tomato cultivars regardless of gene for resistance. Similarly, quantitative comparisons of ion leakage from different tomato cultivars treated with purified race 1 toxin failed to support an earlier report that the toxin was cultivar-specific. Nonhost plant species were unaffected by the toxin. The toxin stimulated the respiratory rates of tomato and of nonhost species tobacco and pepper.