Deciphering the impact of temperature on the conversion capacity and the mycoviral load of conidia of hypovirulent isolates of Cryphonectria parasitica

The European chestnut (Castanea sativa) is an economically important tree for its nut production, timber, and ornamental value. Its cultivation has been significantly challenged by the invasive fungal pathogen Cryphonectria parasitica, which causes chestnut blight. One of the most important disease control strategies relies on hypovirulence, mediated by the infection of the fungal host by the mycovirus Cryphonectria hypovirus 1 (CHV-1). CHV-1 was shown to be horizontally transmitted by hyphal anastomosis among vegetatively compatible fungal individuals and vertically transmitted through conidia. However, little is known about the impact of temperature on the conversion capacity of hypovirulent strains and the viability of conidia and the mycoviral load, which were addressed in the present study. In the first experiment, hypovirulent isolates of C. parasitica were grown at different temperatures to assess the quantity of produced pycnidia and conidia and the viability and proportion of spores carrying CHV-1. In a second experiment, the conversion capacity of virus-containing strains was investigated by co-culturing them with compatible virulent strains at different temperatures. In a third experiment, conidial suspensions of determined concentrations were exposed to different temperature ranges for varying periods of time to investigate the impact on the viability of discharged spores and the dissemination of CHV-1. Considering the warming effect due to climate change, knowledge about the temperature resilience of the Cryphonectria-Hypovirus pathosystem is essential to improve disease management strategies based on biological control with hypovirulence