VIEW ARTICLE

Physiology and Biochemistry

Host-Pathogen Interactions as Measured by Bioassay of Metabolites as Produced by Hypoxylon mammatum with its Host Populus tremuloides. D. H. Griffin, Department of Environmental and Forest Biology, College of Environmental Science and Forestry, Syracuse, NY 13210; P. D. Manion, Department of Environmental and Forest Biology, College of Environmental Science and Forestry, Syracuse, NY 13210. Phytopathology 75:674-678. Accepted for publication 20 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-674.

Five single-ascospore isolates of Hypoxylon mammatum were used to produce metabolites in a chemically defined broth medium and in grain cultures. After treatment to remove high-molecular-weight materials, the culture filtrates and grain culture extracts were concentrated and tested for toxic activity against nine clones of Populus tremuloides by using a leaf-puncture bioassay. The intensity of the reaction was measured by testing serial dilutions of the samples, and sensitivity of the host was measured according to the size of lesion produced at each dilution. The response was dependent on time and concentration of the materials. Both metabolite production methods gave preparations that yielded similar results. The aspen clones could be classified into three sensitivity groups by the bioassays, high, medium, and low. Analysis of variance indicated that horizontal response (clone main effects) was most important, but significant (although quantitatively less important) vertical response mechanisms (clone by isolate interactions) were also present. The host reactions were also compared to canker development data and showed negative correlation to canker length and positive correlation to frequency of callus formation. These correlations suggest that the bioassay of the sensitivity to the metabolites produced in culture by these methods measures the ability of the aspen clones to respond to elicitors. Metabolite-producing abilities of the fungal isolates were not related to their canker-forming abilities when inoculated into the trees.