Vertical Transmission of Fusarium circinatum Mitoviruses FcMV1 and FcMV2-2 via Microconidia

Pine Pitch Canker disease, caused by the pathogenic fungus Fusarium circinatum, affects conifer species worldwide. However, the virulence of the pathogen may be affected by the presence of mycoviruses. The aim of this laboratory-based study was to investigate the probability and rate of transmission of F. circinatum mitoviruses FcMV1 and FcMV2-2 via microconidia. Ten isolates of mitovirus-infected F. circinatum were subcultured to produce a total of 100 single-spore colonies (ten replicates per isolate). The total RNA and cDNA obtained from each spore isolate (monosporic culture) were amplified by PCR with specific primers for detection of F. circinatum mitoviruses FcMV1 and FcMV2-2. The mitoviruses were detected in a high percentage of the individual spore isolates (between 60% and 100% depending on the fungal isolate). However, the probability of transmission was not statistically significantly associated with either the F. circinatum isolate or the viral strain. A high proportion of transmission via microconidia is critical for development of a biological control program against Pine Pitch Canker (PPC) disease in forests. However, further studies are needed to establish the effect of these mitoviruses on the virulence of F. circinatum.