Three new mycoviruses identified in the apple replant disease (ARD)-associated fungus Rugonectria rugulosa

A virus from Aspergillus cibarius with features of alpha- and betachrysoviruses

From the ascomycete Aspergillus cibarius strain NW-FVA 2590, which was originally isolated from a root, associated with stem collar necrosis of Fraxinus excelsior L., a novel virus was isolated and characterized. Its genome is encoded on three monocistronic dsRNA segments ranging from 3683 bp (dsRNA 1) over 3093 (dsRNA 2) to 2902 bp (dsRNA 3), which are packed in isometric particles of around 35 nm. While the viral RdRp (P1) is encoded on segment 1, protein sequencing showed that two more structural proteins are present which are translated from dsRNA 2 (P2) and dsRNA 3 (P3) and possibly form the viral capsid. Additionally, P2 and P3 may undergo posttranslational modifications since the detected proteins bands deviated from the calculated sizes. Due to its phylogenetic position, the novel virus was grouped in the family of Chrysoviridae and was tentatively denominated as Aspergillus cibarius chrysovirus 1 (AcCV1). Due to its composition, biological properties and phylogenetic position, distant from the genera Alphachrysovirus and Betachrysovirus, we suggest to position AcCV1 in a proposed genus "Gammachrysovirus".

Seven new mycoviruses identified from isolated ascomycetous macrofungi

Mycoviruses have been described in all major fungal taxonomic groups. There has been much focus on commercially cultivated basidiomycetous macrofungi, while attention to viruses from ascomycetous macrofungi is lacking. Therefore, in this study, we conducted viral screening against fungal mycelia that were regenerated from ascomycetous macrofungi using agarose gel electrophoresis (AGE) and fragmented and primer-ligated dsRNA sequencing (FLDS). Among the 57 isolates, four isolates were detected with virus-like bands through screening with AGE, and subsequent FLDS analyses determined the viral sequences. Other isolates without virus-like bands in AGE were pooled to check for viral sequences. Using FLDS analysis, a total of seven new mycoviruses were identified, including two double-stranded RNA (dsRNA) viruses belonging to Quadriviridae and Partitiviridae, five positive-sense single-stranded RNA (ssRNA) viruses (three belonging to Mitoviridae, one belonging to Endornaviridae and one belonging to Virgaviridae). All viruses characterized in this study are novel species, and all the hosts are firstly reported to be infected by mycoviruses. These findings expand our knowledge of the diversity of mycoviruses from macrofungi in natural environments.

Fungal Viruses Unveiled: A Comprehensive Review of Mycoviruses

Mycoviruses (viruses of fungi) are ubiquitous throughout the fungal kingdom and are currently classified into 23 viral families and the genus botybirnavirus by the International Committee on the Taxonomy of Viruses (ICTV). The primary focus of mycoviral research has been on mycoviruses that infect plant pathogenic fungi, due to the ability of some to reduce the virulence of their host and thus act as potential biocontrol against these fungi. However, mycoviruses lack extracellular transmission mechanisms and rely on intercellular transmission through the hyphal anastomosis, which impedes successful transmission between different fungal strains. This review provides a comprehensive overview of mycoviruses, including their origins, host range, taxonomic classification into families, effects on their fungal counterparts, and the techniques employed in their discovery. The application of mycoviruses as biocontrol agents of plant pathogenic fungi is also discussed.