Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Division of Plant and Soil Sciences
Chestnut blight, caused by the non-native fungus Cryphonectria parasitica, has decimated American chestnut (Castanea dentata) populations throughout the eastern U.S. over the last century. Biological control of blight, termed hypovirulence, has emerged naturally in the form of a debilitating hypovirus transmitted through hyphal anastomosis among vegetatively compatible C. parasitica strains. Six unlinked vegetative incompatibility (vic) loci regulate hyphal anastomosis and thus, hypovirus transmission, which has limited biocontrol efficacy in genotypically diverse communities. Recently, four of six vic loci have been disrupted to engineer two “super donor” or SD strains. In combining these strains, enhanced transmission of hypovirus to virulent strains is observed regardless of vic genotype of the recipient strain. Recently, the efficacy of the SD strains containing the CHV1/EP713 hypovirus has been field-tested on natural infections of American chestnut in a forest setting. Compared to a treatment containing hypovirulent EU-5/EU-6 strains, the SD treatment results in significant reduction in canker expansion and decreased mortality after one year. However, expansion between 4 and 12 months in previously controlled cankers raises concerns about application method and hypovirus efficacy. To explore performance optimization of SD strains, this study was initiated using the same SD strains with either the CHV1/Euro7 or CHV1/EP713 hypovirus on both natural and artificially-initiated cankers. Three application methods were used on cankers to deliver SD treatment inoculum: punch (previous study), scratch, or paint treatment. A total of 50 stems were assigned one hypovirus/application combination. Stems were measured quarterly and sampled at 12-months post inoculation. Canker expansion and mortality were monitored to permit short- and long-term comparisons. Overall, the punch application type and CHV1/Euro7 hypovirus showed greater inhibition of canker expansion. Canker size and recovery of hypovirus were correlated, suggesting that smaller canker sizes were a direct result of hypovirus transmission. The results of this study support further optimization through comparisons among hypovirus and application method to increase field efficacy of super donor formulations of C. parasitica.
Metheny, Amy Michelle, "Optimization of engineered super donor strains of Cryphonectria parasitica to reduce canker expansion in a forest setting" (2019). Graduate Theses, Dissertations, and Problem Reports. 3818.