Two novel dsRNA mycoviruses were found in different isolates of Diplodia fraxini, NW FVA 1581 and NW FVA 1706, which were isolated from a root, associated with stem collar necrosis of Fraxinus excelsior L. Both mycelia are infected by a novel fusagravirus, which was named Diplodia fraxini fusagravirus 1 (DfFV1), and isolate NW FVA 1706 is additionally infected by a novel partitivirus, which was denominated as Diplodia fraxini partitivirus 1 (DfPV1). The one-segmented, bicistronic genome of DfFV1 is composed of about 8,500 bp. Their ORFs are connected by a 1 slippery heptamer sequence and the 3’ terminal ORF is coding for the viral RdRp. The genome of DfPV1 is composed of three, monocistronic dsRNA segments ranging from 1,755 bp (dsRNA 1) over 1,588 bp (dsRNA 2) to 1,233 bp (dsRNA 3). Based on genome organization and phylogenetic positions, DfFV1 was assigned to the proposed family of “Fusagraviridae” and DfPV1 to the genus Gammapartitivirus within the family of Partitiviridae.
Ultra-structural analysis showed that polysomal structures were stabilized in the single infection and none of these structures could be isolated in the double infection. It is assumed that DfFV1 has an opportunistic lifestyle, being either protected by ribosomes or by transcapsidation from particles of DfPV1.