Viral driving force on virulence differentiation of a rice phytopathogenic fungus and the implication for biocontrol

Viruses are the most abundant biological entities in natural environments. Mycoviruses or fungal viruses are viruses that infect fungi and are being increasingly recognized. However, their ecological function in regulating microbial communities is not well understood. Here, we analyzed the differentiation of the biological characteristics of 32 Rhizoctonia solani strains isolated from rice and confirmed that there was obvious differentiation, especially in virulence. Screening of dsRNA and sequence determination showed that all 32 strains carried viruses displaying a high virus-carrying rate, which was composed of a diverse variety of mycoviruses showing genetic relationships with 15 different families and unclassified virus. In addition, we conducted experiments on multiple horizontal viral infections via hyphal anastomosis between different strains, a simulated ecological environment in a culture dish, and evaluated the dsRNA profiles and virulence of the derivative strains. The results revealed that R. solani strains might suffer multiple infections of mycoviruses via mycelial contact between a multitude of strains and lead to virulence differentiation, thus confirming that mycoviruses are an important driving force of virulence differentiation in this fungus. Moreover, a hypovirulent strain, DWZ-6, was obtained via multiple horizontal viral transfers. Overall, this study provides insights into the ecological implications of mycovirus infection in the virulence differentiation of plant pathogenic fungi and the means of obtaining hypovirulent strains with biological control potential, all of which might serve as a basis for monitoring epidemics of fungal plant disease and developing an environmentally friendly biological control approach.