Transmission of Cryphonectria Hypovirus 1 (CHV1) to Cryphonectria radicalis and In Vitro and In Vivo Testing of Its Potential for Use as Biocontrol Against C. parasitica

Cryphonectria hypovirus 1 (CHV1) is successful in controlling <i>Cryphonectria parasitica</i>, the causal agent of chestnut blight, but little is known regarding its transmission to other fungi, for example the European <i>Cryphonectria radicalis</i>. In this study, CHV1 was transmitted (circa 200,000-800,000 copies/microliter) to seven <i>C. radicalis</i> isolates from infected <i>C. parasitica</i>. Reverse transmission to virus-free <i>C. parasitica</i> (European 74 testers collection) was achieved, although it was less successful (250-55,000 copies/µL) and was dependent on the vegetative compatibility (VC) group. In <i>C. radicalis</i>, the virus infection led to colony colour change from pink to white and smaller colonies, dependent on the virus concentration. The virus was concentrated in the colony edges, and vertically transmitted to 77% of conidia. However, several in vitro experiments demonstrated that <i>C. radicalis</i> was always outcompeted by the blight fungus, only suppressing the pathogen between its 25-50% inoculum level. It presented good secondary capture only when acting as a pioneer. Two types of <i>in planta</i> assays (individual and challenge inoculations) were undertaken. <i>Cryphonectria radicalis</i> behaved as a saprotroph, while chestnut blight fungus behaved as an aggressive pathogen, and lesions after treatment with <i>C. radicalis</i> were no smaller in general, only when using cut branches. Overall, the results showed that infected <i>C. radicalis</i> was unable to control cankers.