Informative value of canker morphology on the presence or absence of virus infection in chestnut blight cankers

Summary Chestnut blight destroyed the native chestnut forests in North America and also severely affected the European chestnut trees after its introduction in the 20th century. The ascomycete fungus Cryphonectria parasitica is responsible for this serious disease and causes lethal bark cankers on susceptible chestnut trees. In Europe, however, an infection of C. parasitica with Cryphonectria hypovirus 1 (CHV‐1) causes hypovirulence in C. parasitica and reduces the severity of the disease. Hypovirulence biologically controls chestnut blight in many regions to date. In this study, our goal was to determine morphological canker characteristics that are indicative of virus presence or absence in C. parasitica. We investigated 677 chestnut blight cankers from seven different geographic locations across Europe. For each canker, we assessed canker length, stem encircling, canker depth, presence of sporulation, canker activity and virus infection. We statistically analysed the informative value of these morphological characteristics for the presence or absence of CHV‐1. However, we did not find reliable indicators. Our logistic regression analysis revealed that virus infection of C. parasitica is not clearly related to canker morphology. This implies that fungal isolations from chestnut blight cankers and assessments in the laboratory are required to determine infection with CHV‐1 unequivocally.