Complete genome sequence of a novel member of the genus Alphafusarivirus isolated from Setosphaeria turcica

This study isolated and characterized a novel positive-sense single-stranded RNA (+ ssRNA) mycovirus from Setosphaeria turcica , the phytopathogenic fungus causing maize northern leaf blight in Yunnan Province, which was tentatively designated as Setosphaeria turcica fusarivirus 2 (StFV2). The complete genome of StFV2 is 6,609 nucleotides in length with a GC content of 45%, and RACE amplification results confirmed that the viral genome lacks a poly(A) tail. Its genome comprises two open reading frames. ORF1 encodes a replication-associated protein that contains an RNA-dependent RNA polymerase domain with the conserved GDD motif and an SF2-type helicase domain. ORF2 encodes a putative hydrophilic auxiliary protein. Sequence alignment analysis revealed that StFV2 shares the closest phylogenetic relationship with Setosphaeria turcica fusarivirus 1 (StFV1, accession no. MW489564) derived from S. turcica. The overall genomic nucleotide identity between the two viruses is 60.86%, while the amino acid sequence identities of ORF1 and ORF2 are 69.12% and 54.21%, respectively. Phylogenetic analysis verified that StFV2 belongs to the genus Alphafusarivirus within the family Fusariviridae . In accordance with the species demarcation criteria of the International Committee on Taxonomy of Viruses (ICTV) for the genus Alphafusarivirus , a strain with more than 20% sequence divergence in the full-length RdRp protein is defined as a novel species member. Thus, StFV2 should be classified as a novel member of the genus Alphafusarivirus . This study enriches the mycovirus resource repertoire associated with S. turcica, and provides a theoretical foundation for further exploring the interaction mechanisms between mycoviruses and fungal pathogens, as well as for excavating biocontrol agents against maize northern leaf blight.