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A Hypoxylon mammatum Pathotoxin Responsible for Canker Formation in Quaking Aspen. Arthur L. Schipper, Jr., Principal Plant Physiologist, North Central Forest Experiment Station, U.S. Department of Agriculture, Forest Service, 1992 Folwell Avenue, St. Paul, MN 55108; Phytopathology 68:866-872. Accepted for publication 30 November 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-866.

A toxic substance produced by the fungus Hypoxylon mammatum was responsible for canker formation in quaking aspen (Populus tremuloides). Cell-free extracts of culture medium and cankered host tissue caused inhibition of wound callus formation, bark necrosis and collapse, and distal vein necrosis in aspen leaves. Twenty-three of 24 H. mammatum isolates and two other fungus species, Cenangium singulare and H. rubigosum, produced substances in culture that were toxic to aspen leaves. Twenty-seven plant species were tested by leaf assay for toxin sensitivity. Only P. tremuloides was highly sensitive to the H. mammatum toxin. Several other poplars, one willow species, and bur oak also gave weak positive reactions. The toxic substances has a molecular weight of between 700 and 1,100 daltons, is heat stable, is soluble in polar solvents, and can be partially purified either by gel filtration, silica gel column and thin-layer chromatography, or high-vaccuum sublimation.