Abstract
Mycoviruses associated with hypovirulence are potential biological control agents and could be useful to study the pathogenesis of fungal host pathogens. Sclerotium rolfsii, a pathogenic fungus, causes southern blight in a wide variety of crops. In this study, we isolated a series of dsRNAs from a debilitated S. rolfsii strain, BLH-1, which had pronounced phenotypic aberrations including reduced pathogenicity, mycelial growth and deficient sclerotia production. Virus-curing and horizontal transmission experiments that eliminated or transmitted, respectively, all dsRNA elements showed that the dsRNAs were involved in the hypovirulent traits of BLH-1. Ultrastructure examination also showed hyphae fracture and cytoplasm or organelle degeneration in BLH-1 hyphal cells compared to the virus-free strain. Three assembled cDNA contigs generated from the cDNA library cloned from the purified dsRNA indicated that strain BLH-1 was infected by at least three novel mycoviruses. One has similarity to the hypovirulence-associated Sclerotinia sclerotiorum hypovirus 2 (SsHV2) in the family Hypoviridae, and the other two are related to two different unclassified dsRNA mycovirus families. To our knowledge, this is the first report of S. rolfsii hypovirulence that was correlated with its associated dsRNA.
Highlights
Mycoviruses are widely described in major fungal groups, including most of the plant-pathogenic fungi (Ghabrial and Suzuki, 2009; Pearson et al, 2009; Xie and Jiang, 2014)
The S. rolfsii strain BLH-1 produced no sclerotia when cultured on potato dextrose agar (PDA) for more than 6 months, whereas the other S. rolfsii strain, LJ-01, contained no double-stranded RNA (dsRNA) element that can form sclerotia, an S. rolfsii trait
We provided the first evidence of hypovirulence caused by dsRNA elements in S. rolfsii
Summary
Mycoviruses ( denoted as fungal viruses) are widely described in major fungal groups, including most of the plant-pathogenic fungi (Ghabrial and Suzuki, 2009; Pearson et al, 2009; Xie and Jiang, 2014). A hypovirulence-associated DNA virus, SsHADV1, showed the ability to control Sclerotinia disease under field conditions (Yu et al, 2010, 2013), similar to Rosellinia necatrix megabirnavirus 1 (RnMBV1), which showed significant potential for Hypovirulence of Sclerotium rolfsii the biological control of apple white root rot disease (Chiba et al, 2009). Due to their potential use in biological control, studying the phenomenon of mycovirus-mediated hypovirulence is attractive for numerous researchers. The hypovirulence-associated mycoviruses, which have divergent molecular characteristics, will enhance our understanding of virus diversity and evolution and contribute to the establishment of host-mycovirus systems (i.e., Cryphonectria parasiticahypovirus, Helmintosporium victoriae-HvV190S, Sclerotinia sclerotiorum-mycovirus, Rosellinia necatrix-mycovirus, and Fusarium graminearum- mycovirus), which are beneficial for studying virus-host interactions including fungal and viral pathogenesis at the molecular level (Xie and Jiang, 2014; Wang et al, 2015)
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