In 2016, the order Mononegavirales was emended through the addition of two new families (Mymonaviridae and Sunviridae), the elevation of the paramyxoviral subfamily Pneumovirinae to family status (Pneumoviridae), the addition of five free-floating genera (Anphevirus, Arlivirus, Chengtivirus, Crustavirus, and Wastrivirus), and several other changes at the genus and species levels. This article presents the updated taxonomy of the order Mononegavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV).

We have determined the full-length 14,491-nucleotide genome sequence of a new plant rhabdovirus, alfalfa dwarf virus (ADV). Seven open reading frames (ORFs) were identified in the antigenomic orientation of the negative-sense, single-stranded viral RNA, in the order 3'-N-P-P3-M-G-P6-L-5'. The ORFs are separated by conserved intergenic regions and the genome coding region is flanked by complementary 3' leader and 5' trailer sequences. Phylogenetic analysis of the nucleoprotein amino acid sequence indicated that this alfalfa-infecting rhabdovirus is related to viruses in the genus Cytorhabdovirus. When transiently expressed as GFP fusions in Nicotiana benthamiana leaves, most ADV proteins accumulated in the cell periphery, but unexpectedly P protein was localized exclusively in the nucleus. ADV P protein was shown to have a homotypic, and heterotypic nuclear interactions with N, P3 and M proteins by bimolecular fluorescence complementation. ADV appears unique in that it combines properties of both cytoplasmic and nuclear plant rhabdoviruses.

“Mal de Río Cuarto” (MRC) is the most important viral disease affecting corn in Argentina. Reovirus-like particles were observed in diseased plants (1,4) and were later serologically related to an isolate of maize rough dwarf virus (3), though this relationship was recently questioned (2). Based on estimates of the prevalence and severity of MRC and yield losses, government agencies, corn hybrid seed companies, and growers agreed that the worst epidemic in the country occurred during the 1996 to 1997 agricultural year. Approximately 300,000 ha of corn were affected by the disease and yield losses were estimated at $120 million. Affected areas included the central and southern Santa Fe, the central, northern, southeastern, and western Buenos Aires, and the eastern and southern (originally the endemic center of MRC in Río Cuarto County) parts of Córdoba. Virus infections were confirmed by double-antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) in root samples from each surveyed location, using an antiserum to MRC virus. The occurrence of MRC in non-endemic areas suggests an unusual phenological coincidence of high vector populations, abundant natural virus reservoirs, and susceptible stages in the crop. Most commercial hybrids surveyed were apparently susceptible to the virus, although some were tolerant. References: (1) O. E. Bradfute et al. Phytopathology 71:205, 1981. (2) C. Marzachi et al. Sem. Virol. 6:103, 1995. (3) R. G. Milne et al. Phytopathology 73:1290, 1983. (4) S. F. Nome et al. Phytopathol. Z. 101:7, 1981.

A virus causing chlorotic mottling symptoms on sunflower was found in various locations in Argentina. Symptoms were small chlorotic spots, yellow blotches on leaves, and plant stunting. Virus transmission efficiency by mechanical inoculation was 73 to 100%, and by Myzus persicae was 31 to 49%. The host range included members of the Amaranthaceae, Asteraceae, Chenopodiaceae, and Solanaceae families. Electron microscopy of leaf dips from infected plants revealed flexuous particles 17 nm wide and 770 nm long. Cytoplasmic laminar aggregates and pinwheel inclusions were observed in ultrathin sections. Purified virus preparations analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis resolved a capsid protein of 33 kDa. A monoclonal antibody to aphid-transmitted potyviruses reacted with the capsid protein of this virus. In dot blot immunoassays, a polyclonal antiserum (early bleeding) reacted with infected sunflowers and weakly with Bidens mottle potyvirus, but not with either maize dwarf mosaic potyvirus or potato virus Y. The evidence suggests that a potyvirus is infecting sunflower, and a partial characterization of the causal agent is reported.

Alfalfa (Medicago sativa L.) is a major forage crop in Argentina with an estimated cultivated area of 4 million ha in the 2009–2010 season, which constitutes a primary component for the animal production chain. In early summer of 2010, alfalfa plants showing virus-like symptoms were identified in 20 commercial fields in La Pampa Province with 95% disease prevalence. Diseased plants had shortened internodes, a bushy appearance, deformations, puckering, epinasty of leaflet blades, vein enations, and varying sized papillae on the adaxial leaflet surfaces. Similar symptoms were observed in alfalfa crops in Buenos Aires, Cordoba, Santa Fe, and Santiago del Estero provinces. Electron microscopy (EM) and molecular assays were performed on leaf tissue from one asymptomatic and two symptomatic plants. EM of ultrathin sections revealed membrane-bound bullet-shaped particles associated with the endoplasmic reticulum of phloem cells from symptomatic plants only. Total RNA was extracted from symptomatic and asymptomatic plants with the RNeasy Plant Mini Kit (Qiagen, Hilden, Germany) for a template in one-step reverse transcription (RT)-PCR assays with the Access RT-PCR Kit (Promega, Madison, WI). RT-PCR assays employed degenerate primers targeting conserved regions of plant rhabdovirus polymerase (L) genes (2). An amplicon of approximately 1 kilobase pairs (detected only from symptomatic plants) was gel purified with the Wizard SV Gel and PCR Clean-Up System (Promega), cloned into pGEM-T Easy Vector System (Promega), and sequenced. Three independents clones were sequenced in both directions at Macrogen Inc. (Korea Republic) to generate a consensus sequence (GenBank Accession No. HQ380230) and compared to sequences of other plant rhabdoviruses available on GenBank. The partial L gene sequence of the alfalfa-infecting rhabdovirus shared highest nucleotide (68.0%) and amino acid (76.5%) sequence identity with the cytorhabdovirus Strawberry crinkle virus (Accession No. AY331390). A phylogenetic tree based on partial amino acid sequences of the polymerase gene indicated the alfalfa-infecting virus was more closely related to cytorhabdoviruses than to nucleorhabdoviruses. Symptoms observed resembled those reported for alfalfa plants infected with a plant rhabdovirus named Alfalfa enation virus (1), which has never been fully characterized. Collectively, the data implicate the observed rhabdovirus as the etiological agent. To our knowledge, this is the first report in Argentina (and South America) of a rhabdovirus infecting alfalfa. Additional field surveys and monitoring of vector/s and yield losses need to be conducted. References: (1) B. Alliot and P. A. Signoret. Phytopathol. Z. 74:69, 1972. (2) R. L. Lamprecht et al. Eur. J. Plant Pathol. 123:105, 2009.