Biological control of chestnut blight by induced mass conidia production of hypovirulent isolates of Cryphonectria parasitica on excised chestnut stems

Abstract

Abstract: The fungus Cryphonectria parasitica is the causative agent of chestnut blight. A group of DsRNA viruses causing the phenomenon hypovirulence, render the fungus less virulent. Hypovirulence is naturally disseminated, but also successfully used as a control method of this devastating plant disease. We used excised chestnut stems as substrate for mass production of hypovirulent conidia of C. parasitica. Perforated stems, to xylem depth, were autoclaved, inoculated with hypovirulent conidial suspension, and incubated until formation of abundant active pycnidia protruding pycnospores through the perforation holes. These were attached to chestnut trees, above and below active chestnut blight cankers, induced previously by inoculation of virulent isolates of C. parasitica. We sampled treated cankers 90 days later. Viral dsRNA was isolated from 19 isolates representing converted cankers (hypovirulent). For 10 isolates sequence analysis revealed no differences in any base pair of the CHV1 ORF A region, when compared to the treatment isolate J12, indicating conversion by the isolate on the excised chestnut stems with mass conidia. The remaining 9 samples with 1 or more base pair difference in the ORF A region from our treatment isolate J12, apparently have been converted by local hypovirulent isolates.