Molecular characterization of two new alternaviruses identified in members of the fungal family Nectriaceae

Since the first report in 2009, at least ten additional viruses have been identified and assigned to the proposed virus family Alternaviridae. Here we report two new mycoviruses tentatively assigned to this family, both identified as members of the fungal family Nectriaceae, which were isolated from surface-disinfected apple roots (Malus x domestica, Borkh.) affected by apple replant disease (ARD). ARD is a highly complex, worldwide-occurring disease resulting from plant reactions to a disturbed (micro)-biome and leads to high economic losses every year. The first alternavirus characterized in this study was identified in a Dactylonectria torresensis isolate. The virus was tentatively named dactylonectria torresensis alternavirus 1 (DtAV1) as the first member of the proposed new species Alternavirus dactylonectriae. The second virus was identified in an isolate of Ilyonectria robusta and was tentatively named ilyonectria robusta alternavirus 1 (IrAV1) as the first member of the proposed new species Alternavirus ilyonectriae. Full genomic sequences of the viruses were determined and are presented. Further, we found hints for putative components of a methyl transferase machinery using in silico approaches. This putative protein domain is encoded by segment 2. However, this result only establishes the basis for subsequent studies in which the function must be confirmed experimentally in vitro. Thus, this is the first study where a function is predicted to all three genomic segments within the group of the alternaviruses. These findings provide further insights into the virome of ARD-associated fungi and are therefore another brick in the wall of understanding the complexity of the disease. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00203-023-03477-0.