A novel plant virus with unique properties infecting Japanese holly fern

A novel RNA virus with a bipartite genome has been found associated with an emerging disease affecting Japanese holly fern (Cyrtomium falcatum). Diseased Japanese holly fern plants showed a variety of foliar symptoms and reduction in size. The virus was transmitted by grafting, as well as through spores from an infected plant. Partially purified preparations of the virus from infected ferns contained quasi-spherical particles that ranged from 30 to 40 nm in diameter. Double-stranded RNA (dsRNA) analyses from diseased plants yielded two major molecules of approximately 6.2 and 3.0 kbp in size, together with three other dsRNAs ascertained to be the replicative forms of subgenomic RNAs. The organization of RNA1 of this novel virus resembles that of raspberry bushy dwarf virus (genus Idaeovirus), whereas the genomic RNA2 showed a distinct organization and evolutionary origin. Results of this study indicate that the virus detected in diseased ferns is an undescribed phytovirus, for which the name Japanese holly fern mottle virus (JHFMoV) is proposed. Furthermore, we postulate that JHFMoV has enough distinguishing features to represent the type species of a novel genus of plant viruses. Taking into account the original host of the virus, we propose the name Pteridovirus for this taxon.