Hail-Induced Infections of the Chestnut Blight Pathogen Depend on Wound Size and May Lead to Severe Diebacks.

This study combined phytosanitary surveys, laboratory analyses, and mathematical modeling to show how hail-induced wounds can foster the infections of the blight pathogen , locally associated with extensive dieback of chestnut (). Orchards and coppices located within and outside the assessed dieback area in a single location in the North West of Italy were inspected to appraise the abundance of hail-induced wounds and infections. The incidence of was significantly higher within the dieback area compared with outside (92% versus 60%; < 0.05). Hail-induced wounds were observed on small branches and shoots of all trees sampled within the dieback area, whereas they were less abundant outside (20% of trees), suggesting either that the dieback was directly associated with the injuries caused by the hailstorms or that those injuries may have facilitated infections of . Isolations conducted on 359 branches and shoots showed that hail-induced wounds served as infection courts for and that infections depended on the size rather than on the number of hail wounds. We fitted a logistic model showing that hail-induced wounds whose perimeter was larger than 66 mm were at particular risk of infection. A newly designed geometrical-based model is proposed to relate hailstones size, hail wound perimeter, and the risk of infection. We established that hail-induced wounds are entry points for virulent and hypovirulent strains of , since 6.5% of isolates were infected by Cryphonectria hypovirus-1.