A Novel Strain of Fusarium oxysporum Virus 1 Isolated from Fusarium oxysporum f. sp. niveum Strain X-GS16 Influences Phenotypes of F. oxysporum Strain HB-TS-YT-1hyg.

A novel strain of Fusarium oxysporum virus 1 (FoV1) was identified from the Fusarium oxysporum f. sp. niveum strain X-GS16 and designated as Fusarium oxysporum virus 1-FON (FoV1-FON). The full genome of FoV1-FON is 2902 bp in length and contains two non-overlapping open reading frames (ORFs), ORF1 and ORF2, encoding a protein with an unknown function (containing a typical -1 slippery motif G_GAU_UUU at the 3'-end) and a putative RNA-dependent RNA polymerase (RdRp), respectively. BLASTx search against the National Center for the Biotechnology Information (NCBI) non-redundant database showed that FoV1-FON had the highest identity (97.46%) with FoV1. Phylogenetic analysis further confirmed that FoV1-FON clustered with FoV1 in the proposed genus Unirnavirus. FoV1-FON could vertically transmit via spores. Moreover, FoV1-FON was transmitted horizontally from the F. oxysporum f. sp. niveum strain X-GS16 to the F. oxysporum strain HB-TS-YT-1hyg. This resulted in the acquisition of the F. oxysporum strain HB-TS-YT-1hyg-V carrying FoV1-FON. No significant differences were observed in the sporulation and dry weight of mycelial biomass between HB-TS-YT-1hyg and HB-TS-YT-1hyg-V. FoV1-FON infection significantly increased the mycelial growth of HB-TS-YT-1hyg, but decreased its virulence to potato tubers and sensitivity to difenoconazole, prochloraz, and pydiflumetofen. To our knowledge, this is the first report of hypovirulence and reduced sensitivity to difenoconazole, prochloraz, and pydiflumetofen in F. oxysporum due to FoV1-FON infection.