Co-Infection with Three Mycoviruses Stimulates Growth of a Isolate on Nutrient Medium, but Does Not Induce Hypervirulence in a Natural Host.

and are the most destructive fungal species infecting stone fruit ( species). High-throughput cDNA sequencing of and isolates collected from stone fruit orchards revealed that 14% of isolates were infected with one or more of three mycoviruses: Sclerotinia sclerotiorum hypovirus 2 (SsHV2, genus ), Fusarium poae virus 1 (FPV1, genus ), and Botrytis virus F (BVF, genus ). Isolate M196 of was co-infected with all three viruses, and this isolate was studied further. Several methods were applied to cure M196 of one or more mycoviruses. Of these treatments, hyphal tip culture either alone or in combination with antibiotic treatment generated isogenic lines free of one or more mycoviruses. When isogenic fungal lines were cultured on nutrient agar medium in vitro, the triple mycovirus-infected parent isolate M196 grew 10% faster than any of the virus-cured isogenic lines. BVF had a slight inhibitory effect on growth, and FPV1 did not influence growth. Surprisingly, after inoculation to fruits of sweet cherry, there were no significance differences in disease progression between isogenic lines, suggesting that these mycoviruses did not influence the virulence of on a natural host.