Abstract
Fusarium wilt caused by Fusarium oxysporum f. sp. momordicae (FoM) is an important fungal disease that affects the production of bitter gourd. Hypovirulence-associated mycoviruses have great potential and application prospects for controlling the fungal disease. In this study, a novel ourmia-like virus, named Fusarium oxysporum ourmia-like virus 1 (FoOuLV1), was isolated from FoM strain HuN8. The viral genomic RNA is 2,712 nucleotides (nt) in length and contains an open reading frame (ORF) encoding a putative RNA-dependent RNA polymerase (RdRp) using either standard or mitochondrial codes. In strain HuN8, there was also a FoOuLV1-associated RNA segment with 1,173 nt in length with no sequence homology. Phylogenetic analysis showed that FoOuLV1 is a member of the genus Magoulivirus of the family Botourmiaviridae. FoOuLV1 was found to be associated with hypovirulence in FoM. Moreover, FoOuLV1 and its hypovirulence trait can be transmitted horizontally to other FoM strains and also to other formae speciale strains of F. oxysporum. In addition, FoOuLV1 showed significant biological control effect against the bitter gourd Fusarium wilt. To our knowledge, this study reveals the first description of a hypovirulence-associated ourmia-like mycovirus, which has the potential to the biological control of Fusarium wilt.
Highlights
Mycoviruses are widespread in all major filamentous fungi, yeasts, and oomycetes (Xie and Jiang, 2014; Ghabrial et al, 2015)
We identified and characterized a novel hypovirulence-inducing ourmia-like mycovirus from F. oxysporum f. sp. momordicae named Fusarium oxysporum ourmia-like virus 1 (FoOuLV1) and verified its hypovirulence trait and its horizontal transmission ability
Based on the RT-polymerase chain reaction (PCR) analysis, we found that FoOuLV1 was harbored in f. sp. momordicae (FoM) strain HuN8, which was isolated from the stem of a diseased bitter gourd plant collected in Hunan Province, China
Summary
Mycoviruses are widespread in all major filamentous fungi, yeasts, and oomycetes (Xie and Jiang, 2014; Ghabrial et al, 2015). According to a recent study, more than 300 mycoviral sequences have been logged in the National Center for Biotechnology Information (NCBI) database (Zhou et al, 2020), which are grouped into at least 19 families by the International Committee on Taxonomy of Viruses (ICTV). Most mycoviruses have double-stranded RNA (dsRNA); some mycoviruses have positive single-stranded RNA (+ssRNA), and a few mycoviruses have single-stranded DNA (ssDNA) or negative single-stranded RNA (−ssRNA; Ghabrial and Suzuki, 2009; Xie and Jiang, 2014; Ghabrial et al, 2015). The ssRNA mycoviruses are grouped into seven families: Alphaflexiviridae, Barnaviridae, Botourmiaviridae, Gammaflexiviridae, Hypoviridae, Mymonaviridae, and Narnaviridae (Amarasinghe et al, 2018). There are unclassified mycoviruses (Li H. et al, 2019).
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