[en] Highlights: • Ectomycorrhizal fungi host a diverse lineages of mycoviruses. • Eight novel viruses from four families have been characterized in Picoa juniperi. • New members of fusagra-, yado-kari- and megatotiviruses have been identified. • PjMTV1 is the secondly recorded member of the proposed family “Megatotiviridae”. • PjMTV1 has the longest genome among monopartite dsRNA viruses ever known so far. Viruses hosted by ectomycorrhizal fungi remain poorly studied. In this study, we detected eight new fungal viruses co-infecting a single isolate of the hypogeous ectomycorrhizal fungus Picoa juniperi using high-throughput sequencing. Phylogenetic analysis of one identified virus abbreviated as PjMTV1 revealed its closest relatives as members of the newly proposed family “Megatotiviridae”. Phylogenetic analyses of two identified viruses abbreviated as PjV1 and PjV2 showed that these viruses are associated with members of the proposed family “Fusagraviridae”. Phylogenetic analysis of the identified one another virus abbreviated as PjYV1 demonstrated that this virus is related to the members of the proposed family Yadokariviridae. The remaining four identified virus-like contigs were determined as segments of the bipartite dsRNA mycoviruses from the family Partitiviridae. The mycoviruses reported in this study are the first viruses described in Picoa juniperi, and PjMTV1 characterized herein is the secondly reported member of the newly proposed family “Megatotiviridae”.