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Physiology and Biochemistry

Effect of Phytotoxins Produced by Botryosphaeria obtusa, the Cause of Black Rot of Apple Fruit and Frogeye Leaf Spot. P. Venkatasubbaiah, Department of Botany, North Carolina State University, Raleigh 27695; T. B. Sutton(2), and W. S. Chilton(3). (2)(3)Department of Plant Pathology, and Department of Botany, respectively, North Carolina State University, Raleigh 27695. Phytopathology 81:243-247. Accepted for publication 17 August 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-243.

Botryosphaeria obtusa, which causes black rot of apple fruit and frogeye leaf spot, produced phytotoxins in culture, infected fruit, and spore germination fluids. Mellein was the most abundant toxin isolated from the culture fluid. Other toxins isolated were tyrosol, 4-hydroxymellein, 5-hydroxymellein, and 4-hydroxybenzaldehyde. Seventeen apple cultivars and eight weed species were used in a leaf bioassay to determine phytotoxicity of the toxins. The apple cultivars, Supergold and Silverspur, were highly sensitive to all toxins. Only three apple cultivars showed moderate resistance to most toxins. There was no correlation between isolate pathogenicity and the amount of toxin production in culture. Among the weed species, prickly sida and morning glory were very sensitive. Extraction of fruit infected with B. obtusa yielded all toxins except 4-hydroxybenzaldehyde. When conidial germination fluids were extracted with solvent, mellein and 4-hydroxymellein could be detected by thin-layer chromatography.