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Hypoxylon mammatum Ascospore Infection of Populus tremuloides Clones: Effects of Moisture Stress in Tissue Culture. R. R. Bélanger, College of Environmental Science and Forestry, State University of New York, Syracuse 13210, Present address: Dept. de Phytologie, FSAA, Université Laval, Ste-Foy, Québec G1K 7P4; P. D. Manion, and D. H. Griffin. College of Environmental Science and Forestry, State University of New York, Syracuse 13210. Phytopathology 79:315-317. Accepted for publication 15 September 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-315.

Tissues from six aspen clones were cultured to produce plantlets from dormant buds. Plantlets of 1–2 cm were moisture stressed by adding various concentrations of mannitol to the growth medium. Inoculation of unwounded plantlets with ascospores of Hypoxylon mammatum resulted in visible signs of mycelium after 3–4 days. After 10 days, mycelial growth on controls and moderately stressed plants remained superficial; in contrast, highly stressed plants were invaded by the mycelium and exhibited necrotic lesions at the site of inoculation. The level of moisture stress needed for mycelium invasion and lesion development varied (–0.45 to –1.2 MPa) among the clones. Clonal differences observed could be applied in basic physiological studies or in aspen breeding programs for hypoxylon canker resistance.