Insect hypovirulence-associated mycovirus confers entomopathogenic fungi with enhanced resistance against phytopathogens

Mycoviruses can alter the biological characteristics of host fungi, including change virulence or pathogenicity of phytopathogens and entomopathogenic fungi (EPF). However, most studies on the mycoviruses found in EPF have focused on the effects of the viruses on the virulence of host fungi towards insect pests, with relatively few reports on the effects to the host fungi with regard to plant disease resistance in hosts. The present study investigated the effects of the mycovirus <i>Beauveria bassiana</i> chrysovirus 2 (BbCV2) virus infection on host biological characteristics, evaluated antagonistic activity of BbCV2 against two phytopathogenic fungi (<i>Sclerotinia sclerotiorum</i> and <i>Botrytis cinerea</i>), and transcriptome analysis was used to reveal the interactions between viruses and hosts. Our results showed that BbCV2 virus infection increased <i>B. bassiana</i>‘s growth rate, spore production, and biomass, it also enhanced the capacity of host fungi and their metabolic products to inhibit phytopathogenic fungi. BbCV2 virus infection reduced the contents of the two pathogens in tomato plants significantly, and transcriptome analysis revealed that the genes related to competition for ecological niches and nutrition, mycoparasitism and secondary metabolites in <i>B. bassiana</i> were significantly up-regulated after viral infection. These findings indicated that the mycovirus infection is an important factor to enhance the ability of <i>B. bassiana</i> against plant disease after endophytic colonization. We suggest that mycovirus infection causes a positive effect on <i>B. bassiana</i> against phytopathogens, which should be considered as a potential strategy to promote the plant disease resistance of EPF.