Detection of a Conspecific Mycovirus in Two Closely Related Native and Introduced Fungal Hosts and Evidence for Interspecific Virus Transmission.

is a native fungus in Europe where it behaves as a harmless decomposer of leaves of common ash. Its close relative was introduced into Europe from Asia and currently threatens ash ( sp.) stands all across the continent causing ash dieback. isolates from Europe were previously shown to harbor a mycovirus named (HfMV1). In the present study, we describe a conspecific mycovirus that we detected in . HfMV1 was consistently identified in isolates (mean prevalence: 49.3%) which were collected in the sampling areas before the arrival of ash dieback. HfMV1 strains in both fungal hosts contain a single ORF of identical length (717 AA) for which a mean pairwise identity of 94.5% was revealed. The occurrence of a conspecific mitovirus in and is most likely the result of parallel virus evolution in the two fungal hosts. HfMV1 sequences from showed a higher nucleotide diversity and a higher number of mutations compared to those from , probably due to a bottleneck caused by the introduction of in Europe. Our data also points to multiple interspecific virus transfers from to , which could have contributed to the intraspecific virus diversity found in .