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Isolation of Toxins of Hypoxylon mammatum and Demonstration of Some Toxin Effects on Selected Clones of Populus tremuloides. Bruce A. Stermer, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312; Robert P. Scheffer(2), and John H. Hart(3). (2)Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312; (3)Department of Botany and Plant Pathology (also in Department of Forestry), Michigan State University, East Lansing 48824-1312. Phytopathology 74:654-658. Accepted for publication 12 January 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-654.

Hypoxylon mammatum produces in culture several acidic metabolites that are very toxic to its trembling aspen (Populus tremuloides) host; nonhost species are tolerant. Toxins were partially purified by extraction with solvents, absorption on charcoal, gel filtration, chromatography on silicic acid and DEAE columns, and HPLC. The relative proportions of the toxic metabolites changed with the age of cultures. Clones of P. tremuloides differed in sensitivity; the most resistant clone tolerated 1,000-fold higher concentrations of toxins than did a sensitive clone. Sensitivity / tolerance of stem tissue was correlated with leaf response, as indicated by application to wounded surfaces. For leaf bioassays, drops (10 μl) were applied to a wound on the leaf or to the cut ends of petioles. The latter bioassay, which distributed toxins throughout the leaf blade, was more sensitive. The toxins caused increases in O2 uptake by leaves, followed by necrosis and electrolyte leakage. The data support the hypothesis that toxins of H. mammatum are significant determinants in disease development.