Pathogenicity and Canker Control by Mixtures of Hypovirulent Strains ofEndothia parasiticain American Chestnut

Abstract

Pathogenicity of hypovirulent strains of E. parasitica on American chestnut [Castanea dentata] stems decreased dramatically when 2 or more were mixed. Probably this effect is due to the exchange of genetic hypovirulence factors between strains possessing different factors; i.e., superinfection, and fungal cell death that results from the interaction of strains that are vegetatively incompatible. Pathogenicities of normal and hypovirulent strains of E. parasitica were highly variable and strain dependent. Single hypovirulent strains often are ineffective in controlling cankers, presumably because vegetative incompatibility hinders transfer of factors that confer hypovirulence. Mixtures of different hypovirulent mycelia effectively overcame vegetative incompatibility and rapidly arrested canker development in both laboratory and field tests. However, mixtures tested to date may be too debilitated to survive and disseminate in the wild.