The Mycovirus Cryphonectria Hypovirus 1 Infects the Heterologous Host Fusarium oxysporum and Induces Hypovirulence

ABSTRACT Fusarium oxysporum is a ubiquitous soil‐borne pathogen that causes vascular wilts in a variety of crops. Mycoviruses from plant pathogens have garnered attention as potential biocontrol agents upon the discovery that they can induce hypovirulence (reduced virulence) in their fungal host. In this work we explored the interaction of F. oxysporum f. sp. lycopersici (Fol) with Cryphonectria hypovirus 1 (CHV1) with the aim of contributing to the identification of mycoviruses with biocontrol potential in F. oxysporum . Transfection of Fol protoplasts with an infectious cDNA clone of the virus showed that CHV1 efficiently replicates in this heterologous host, inducing high levels of hypovirulence. The successful application of hypovirulence‐associated mycoviruses to disease control requires that infected strains effectively propagate them in the natural populations of the fungus, which occurs mainly through hyphal anastomosis. Bearing this in mind, we used the hypovirulent transfected Fol strains to conduct in vitro assays of CHV1 transmission to uninfected strains by hyphal anastomosis. These assays corroborated the good potential of CHV1 to spread in Fol. We also exploited this transmission route to construct strains harbouring only the cytoplasmatic RNA copy of the virus, allowing us to further characterise the CHV1–Fol interaction in a condition that resembles natural infections. Taken together our results provide evidence that CHV1 has the ability to infect Fol in a stable manner and to effectively spread its hypovirulent effect horizontally in this host through continuous infections and re‐infections by fusion of vegetative hyphae and germinating conidia within and between individuals.