2020 taxonomic update for phylum Negarnaviricota (Riboviria: Orthornavirae), including the large orders Bunyavirales and Mononegavirales.

In March 2020, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. At the genus rank, 20 new genera were added, two were deleted, one was moved, and three were renamed. At the species rank, 160 species were added, four were deleted, ten were moved and renamed, and 30 species were renamed. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV.

Taxonomy of the family Arenaviridae and the order Bunyavirales: update 2018.

In 2018, the family Arenaviridae was expanded by inclusion of 1 new genus and 5 novel species. At the same time, the recently established order Bunyavirales was expanded by 3 species. This article presents the updated taxonomy of the family Arenaviridae and the order Bunyavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV) and summarizes additional taxonomic proposals that may affect the order in the near future.

A new, widespread emaravirus discovered in blackberry.

A new virus was identified in blackberry plants exhibiting leaf mottling, chlorotic ringspots and curved midribs, symptoms associated with blackberry yellow vein disease (BYVD). The genome of the new virus, provisionally named blackberry leaf mottle-associated virus (BLMaV), was characterized and phylogenetic analysis revealed its close relationship to recognized members of the genus Emaravirus. BLMaV was transmitted by a yet to be described eriophyid mite species, further reinforcing its placement in the genus. Detection protocols were developed and used to determine the presence of the virus in plants collected from several areas in the U.S.A. The incidence of BLMaV was greater than 40% in BYVD-affected material.

A novel emaravirus is associated with redbud yellow ringspot disease.

Yellow ringspot is the only virus-like disease reported in redbud (Cercis spp.) with symptoms including vein clearing, chlorotic ringspots and oak-leaf pattern. A putative new emaravirus was present in all trees displaying typical yellow ringspot symptoms and the name redbud yellow ringspot associated virus is proposed. The virus genome is composed of at least five RNA segments. Two coding regions were studied to determine isolate diversity with results pointing to a homogeneous virus population. Host range was evaluated using graft transmission and by testing species found in close proximity to infected trees. Mite transmission with Aculops cercidis, the predominant species found in redbud trees in the epicenter of the disease, was evaluated but was not found to be a vector of the virus. Based on this study and the accumulated knowledge on emaravirus evolution we propose that speciation is allopatric, with vectors being a major component of the process.

The evolution of emaraviruses is becoming more complex: seven segments identified in the causal agent of Rose rosette disease.

There are few examples of a plant disease as devastating as rose rosette, a disorder that could lead to total loss for the nursery industry and rosarians alike. Although described over 75 years ago, the causal agent of rose rosette remains elusive. Utilizing the bottleneck created during vector transmission and large scale sequencing it was determined that the causal agent of the disease is rose rosette virus (RRV), a member of the genus Emaravirus. The genome structure of emaraviruses displays significant fluidity and for this reason the genome composition of RRV was revisited, leading to the discovery of three additional segments, one of which is predicted to be bicistronic.

Bacterial Leaf Scorch in the District of Columbia: Distribution, Host Range, and Presence of Xylella fastidiosa Among Urban Trees.

A survey of urban trees affected by bacterial leaf scorch (BLS) caused by Xylella fastidiosa was conducted in the District of Columbia during 2011 and 2012. Over 20 species of urban trees were evaluated at 95 sites. Symptomatic and asymptomatic foliage from trees with BLS symptoms and foliage from neighboring asymptomatic trees were sampled. An X. fastidiosa-specific enzyme-linked immunosorbent assay (ELISA) and a polymerase chain reaction assay were used to detect and identify the strains from environmental samples. Symptomatic trees testing ELISA-positive for X. fastidiosa occurred most frequently with Quercus palustris, Q. rubra, Ulmus americana, and Platanus occidentalis. The bacterium was also less frequently identified on eight other symptomatic and five asymptomatic tree species. On infected trees, the bacterium was also detected on the asymptomatic portion of seven tree species. All strains were identified as the X. fastidiosa subsp. multiplex genotype ALSII except on Morus alba, where the genotype ALSI and the subsp. sandyi were detected. The occurrence of crown dieback was found significantly associated with X. fastidiosa-infection on Q. palustris, Q. rubra, U. americana, and P. occidentalis. Because this pathogen continues to perpetuate uncontrolled in urban environments, there is a pressing need to identify long-term management strategies that abate disease.