VIEW ARTICLE

Resistance

Survival of American Chestnut Trees: Evaluation of Blight Resistance and Virulence in Endothia parasitica. G. J. Griffin, Professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061; F. V. Hebard(2), R. W. Wendt(3), and J. R. Elkins(4). (2)(3)Former research associate, and former graduate student, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061; (4)Professor, Division of Natural Sciences, Concord College, Athens, WV 24712. Phytopathology 73:1084-1092. Accepted for publication 2 March 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1084.

Large (22- to 114-cm diameter at breast height [DBH]), surviving American chestnut trees in the natural range were evaluated from 1978 to 1982 for blight resistance and/or the presence of Endothia parasitica strains with low virulence. Canker length measurements following inoculation of virulent E. parasitica on grafted scions, seedlings, and excised stems indicated that some surviving trees are blight resistant. In situ inoculation trials on large, surviving trees with virulent E. parasitica indicated that superficial canker development is also an important characteristic associated with blight resistance in American chestnut. Strains of E. parasitica that produced short, superficial cankers on blight-susceptible American chestnut stump sprouts were associated with large, surviving trees, smaller trees (5- 14 cm DBH) growing near large trees, and small stump sprouts (4- 19 cm DBH). Of 542 isolates tested, 113 (20.8%) had low or intermediate virulence. Eight of eight low-virulence and one of three intermediate isolates tested contained dsRNA. The incidences of low-virulence isolates in the E. parasitica populations from large, surviving trees and from small stump-sprout trees in Virginia-West Virginia were 14.9 and 4.3%, respectively, whereas the incidences of intermediate strains were 13.2 and 2.6%, respectively. Many American chestnut trees may survive because of the combined effects of blight resistance and low virulence of the pathogen, but others may survive because of a single factor.