Determination of the complete genome sequence of European mountain ash ringspot-associated emaravirus from Sorbus intermedia reveals two additional genome segments.

We report the complete genome sequence, comprising six single-stranded RNAs of negative orientation, of a European mountain ash ringspot-associated virus (EMARaV) isolate identified in a diseased Sorbus intermedia (Swedish whitebeam) tree exhibiting prominent chlorotic ringspots, mottle and line pattern on leaves. Since the first observation of EMARaV-like symptoms and detection of the virus in whitebeam in 2012, the tree displayed leaf symptoms every year in at least one third of its canopy, developed dieback symptoms, and showed signs of decline. Two previously unrecorded genome segments of the virus were identified, each encoding a single protein in a negative orientation. RNA5 is 1629 nucleotides long and encodes the putative movement protein (MP) of EMARaV with a molecular mass of 42.4 kDa. RNA6 (1362 nucleotides) encodes a small protein (26.8 kDa) exhibiting some sequence similarity to the P4 protein encoded by EMARaV RNA4. However, its biological function remains to be elucidated. Both novel genome segments are systematically present in EMARaV-infected Sorbus spp., and no additional genome segments could be identified by two independent methods. It is concluded that the six RNAs represent the complete genome of EMARaV.

Taxonomy of the order Bunyavirales: second update 2018.

In October 2018, the order Bunyavirales was amended by inclusion of the family Arenaviridae, abolishment of three families, creation of three new families, 19 new genera, and 14 new species, and renaming of three genera and 22 species. This article presents the updated taxonomy of the order Bunyavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV).

Emaravirus: a novel genus of multipartite, negative strand RNA plant viruses.

Ringspot symptoms in European mountain ash (Sorbus aucuparia L.), fig mosaic, rose rosette, raspberry leaf blotch, pigeonpea sterility mosaic (Cajanus cajan) and High Plains disease of maize and wheat were found to be associated with viruses that share several characteristics. They all have single-stranded multipartite RNA genomes of negative orientation. In some cases, double membrane-bound virus-like particles of 80 to 200 nm in diameter were found in infected tissue. Furthermore, at least five of these viruses were shown to be vectored by eriophyid mites. Sequences of European mountain ash ringspot-associated virus (EMARaV), Fig mosaic virus (FMV), rose rosette virus (RRV), raspberry leaf blotch virus (RLBV), pigeonpea sterility mosaic virus and High Plains virus strongly support their potential phylogenetic relationship. Therefore, after characterization of EMARaV, the novel genus Emaravirus was established, and FMV was the second virus species assigned to this genus. The recently sequenced RRV and RLBV are supposed to be additional members of this new group of plant RNA viruses.

Detection of European mountain ash ringspot-associated virus-specific RNA and protein P3 in the pear leaf blister mite Phytoptus pyri (Eriophyidae).

The means by which European mountain ash ringspot-associated virus (EMARaV), a minus-strand ssRNA virus and the type member of the genus Emaravirus, is naturally spread, is unknown. In attempts to identify an EMARaV vector, galls induced by the eriophyid mite Phytoptus pyri were frequently found on infected leaves. By immunofluorescence microscopy, the presence of EMARaV nucleocapsid protein P3 was demonstrated in P. pyri individuals collected from diseased plants. Furthermore, RT-PCR analysis of entire P. pyri individuals revealed the presence of both viral genomic ss(-)RNAs and antigenomic ss(+)RNAs, suggesting that P. pyri might be a candidate vector of EMARaV.