Abstract:
Species of Armillaria are distributed globally and include some of the most important pathogens
of forest and ornamental trees. Some of them form large long-living clones that are considered as
one of the largest organisms on earth and are capable of long-range spore-mediated transfer as
well as vegetative spread by drought-resistant hyphal cords called rhizomorphs. However, the virus
community infecting these species has remained unknown. In this study we used dsRNA screening and
high-throughput sequencing to search for possible virus infections in a collection of Armillaria isolates
representing three diferent species: Armillaria mellea from South Africa, A. borealis from Finland and
Russia (Siberia) and A. cepistipes from Finland. Our analysis revealed the presence of both negativesense RNA viruses and positive-sense RNA viruses, while no dsRNA viruses were detected. The viruses
included putative new members of virus families Mymonaviridae, Botourmiaviridae and Virgaviridae
and members of a recently discovered virus group tentatively named “ambiviruses” with ambisense
bicistronic genomic organization. We demonstrated that Armillaria isolates can be cured of viruses
by thermal treatment, which enables the examination of virus efects on host growth and phenotype
using isogenic virus-infected and virus-free strains.
