Hypovirulent effect of the Cryphonectria hypovirus 1 in British isolates of Cryphonectria parasitica

Chestnut blight, caused by Cryphonectria parasitica, is controlled in many European countries by the naturally occurring mycovirus Cryphonectria hypovirus 1 (CHV-1). During surveys of recently identified chestnut blight outbreak in England, CHV-1 was detected in several individuals of the pathogen isolated from affected trees. We investigated two of these CHV-1-infected isolates (L-6 and Db-1) as potential biocontrol agents for deployment in the UK comparing their virulence against virus-free (M1275) and hypovirulent (M784) European isolates by inoculating sweet chestnut seedlings.

Both the European CHV-1 M784 hypovirulent isolate and UK L-6 isolate formed significantly smaller lesions in sweet chestnut seedling bark than the other three isolates (Db-1, and virulent isolates FTC121 and M1275). The highest virus concentration was detected in isolate M784, followed by L-6, with the lowest concentration in isolate Db-1. White colony colouration indicative of hypovirulence was common in colonies re-isolated from smaller lesions, and the same isolates also tended to be slower growing in culture, have a higher virus concentration, and caused less epicormic growth and fewer stromata to be present in plants. L-6 and Db-1 virus sequences, respectively, matched the virus haplotype E-5 detected previously in Switzerland and a mutation of the same subtype I haplotype.

Isolate L-6 could potentially act as biocontrol for chestnut blight outbreaks in the UK but further laboratory and field experiments are needed. © 2019 Crown copyright. Pest Management Science © 2019 Society of Chemical Industry.