Effects of Thermal and Antibiotic Treatments on the Viral Accumulation of FcMV1 in Fusarium circinatum Isolates.

Mycoviruses are viruses that infect fungi, including plant pathogens. The infection of these mycoviruses is sometimes associated with impaired phenotypes of their fungal hosts, a phenomenon known as hypovirulence. Thus, using mycoviruses as biological control agents has emerged as a promising tool to combat forest diseases. The invasive ascomycete fungus Fusarium circinatum, which causes pine pitch canker (PPC) disease in Pinus tree species and other coniferous trees, is infected by the mycovirus Fusarium circinatum mitovirus 1 (FcMV1), FcMV2-1, and FcMV2-2. However, its impact on pathogen fitness remains unclear. The most accurate method used to identify the effect of a mycovirus on its host is the generation of isogenic lines with and without the mycovirus. The present study aimed to cure F. circinatum isolates infected by FcMV1 using different approaches. For this purpose, three replicates of each isolate were exposed to thermal treatment (38 °C) and antibiotic treatment (ribavirin, cycloheximide, kanamycin, and rifampicin mixed with cAMP)(cyclic adenosine monophosphate) for five successive passages. The viral titer of FcMV1 was then assessed using qPCR (quantitative polymerase chain reaction) after the first week and after the fifth week of the treatment. The results revealed differences in treatment efficacy among F. circinatum isolates, with some showing very low virus titers at the end of the experiment. Both thermal and antibiotic treatment effectively reduced the viral load in all isolates. In addition, the antibiotic cycloheximide and rifampicin +cAMP reduced the viral titer more than ribavirin and kanamycin. The isolate Fc179 was found to be more prone to antibiotic treatment than the other two isolates (001 and Va221). This study demonstrated the possibility of using some isolates of F. circinatum for fine-tuning cures for mitovirus, in order to create virus-free strains for biological control in the future.