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Physiology and Biochemistry

Effects of Virulent and Hypovirulent Endothia parasitica and Their Metabolites on Ethylene Production by Bark of American and Chinese Chestnut and Scarlet Oak. Frederick V. Hebard, Department of Plant Pathology, University of Kentucky, Lexington 40546-0091; Louis Shain, Department of Plant Pathology, University of Kentucky, Lexington 40546-0091. Phytopathology 78:841-845. Accepted for publication 25 January 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-841.

Ethylene production was stimulated in bark of American chestnut and scarlet oak up to 8 cm from wounds or expanding initial lesions caused by virulent and hypovirulent strains of Endothia parasitica, before lignification. Stimulation of ethylene production ceased when, or soon after, a lignified zone formed and initial lesions stopped expanding. The stimulation of ethylene production was repressed 0.52 cm from the expanding initial lesion in American chestnut inoculated with virulent E. parasitica but not in the other host-treatment combinations. On American chestnut, stimulation of ethylene production with repression close to the canker also was observed for naturally occurring cankers that were expanding because of growth of mycelial fans. Stimulation of ethylene production was not observed for naturally occurring cankers on scarlet oak or Chinese chestnut, possibly because the cankers were not expanding. Mycelium-agar disks of virulent and hypovirulent E. parasitica stimulated ethylene production in bark plugs of American and Chinese chestnut and scarlet oak as compared with controls. American chestnut was stimulated more than scarlet oak and Chinese chestnut. Oxalate, a known metabolite of E. parasitica, inhibited ethylene production in bark plugs of chestnut and oak. Sterile filtrates of virulent and hypovirulent E. parasitica cultures stimulated ethylene production in American chestnut when the fungi were grown on chestnut or oak bark-extract broth but not when the fungi were grown on potato-dextrose broth. Thus both the stimulatory factor(s) and the repressive factor(s) may be present in culture filtrates.