Mycovirus BbOCuV1 infection enhances the host Beauveria bassiana resistance against phytopathogens causing soil born plant diseases

Soil-borne plant diseases caused by Sclerotinia sclerotiorum and Fusarium asiaticum result in yield losses and severely affect grain quality. The entomopathogenic fungus (EPF), Beauveria bassiana, can inhibit a wide range of pathogens in vitro and forms symbioses with plants, inducing resistance to pathogen infection. Mycoviruses have been studied for their role in the biological control of plant pathogens, and can also affect B. bassiana's biological characteristics and virulence against insect pests. However, there is little research on whether mycovirus can affect the resistance of B. bassiana against phytopathogens. In this study, we examined the impact of the mycovirus Beauveria bassiana orthocurvulavirus 1 (BbOCuV1) on the host strain's biological characteristics, its inhibitory effect in vitro on the two phytopathogens S. sclerotiorum and F. asiaticum, and its effect on resistance to infection by the two pathogens after endophytic colonization of the plant. Our results showed that BbOCuV1 infection not only significantly increased the growth rate, spore production, and biomass of B. bassiana, but also the inhibitory effect against the two phytopathogens in vitro and the resistance against their infection after colonization. RNA sequencing analysis revealed that BbOCuV1 infection increased the expression of genes associated with carbon and nitrogen metabolism pathways in B. bassiana. BbOCuV1 infection also increased the expression of genes associated with pathways in secondary metabolite biosynthesis. These results suggested the mechanism by which viral infection increases the host's biomass and phytopathogen-suppressive activity. This study provides a new strategy to utilize EPFs and mycoviruses for the biological control of soil-borne diseases.