Taxonomy, biogeography and importance of Heterobasidion viruses

• Heterobasidion species host partitiviruses, mitoviruses and strains of HetRV6.
• Heterobasidion viruses are able to cross species borders and form co-infections.
• Some Heterobasidion viruses cause phenotypic changes in their hosts.

The genus Heterobasidion consists of several species of necrotrophic and saprotrophic fungi, and includes some of the most detrimental organisms in boreal conifer forests. These fungi host a widespread and diverse mycovirus community composed of more than 16 species of Partitiviridae, a species of Narnaviridae and one taxonomically unassigned virus related to the Curvularia thermal tolerance virus. These viruses are able to cross species borders, co-infect single host strains and cause phenotypic changes in their hosts. The abundance of viruses increases over time in Heterobasidion infection centers, and they are targeted by fungal RNA interference. Long-term field studies are essential for obtaining a comprehensive view of virus effects in the nature.