Protection of American Chestnut with Hypovirulent Conidia of Cryphonectria (Endothia) parasitica. K. L. Scibilia, Former Graduate Research Assistant, Department of Forestry, University of Kentucky, Lexington 40546-0091. L. Shain, Professor, Department of Plant Pathology, University of Kentucky, Lexington 40546-0091. Plant Dis. 73:840-843. Accepted for publication 1 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0840.

Cankers were initiated on American chestnut stems with mycelium of a virulent strain of Cryphonectria (Endothia) parasitica (Ep 155 = ATCC 38755) before or after application of conidia from isogenic strains that contained hypovirulence agents HI₂ from Italy (= strain Ep 780) or HT₂ from Tennessee (= strain Ep 905). Cankers initiated up to 10 wk after the application of conidia yielded cultures with hypovirulent morphology. Within 10 wk after spraying with Ep 780 conidia, 14 of 22 trees had at least one canker that produced hypovirulent inoculum as cirrhi. Conidia from Ep 780 converted significantly more cankers than did conidia from Ep 905. However, there was no significant difference in stem survival between conidial treatments after 1 yr.