Melon yellow spot virus (MYSV), a tentative member of the genus Tospovirus, is considered a distinct serotype due to the lack of a serological relationship with other tospoviruses in its nucleocapsid protein (NP). Recently, a virus isolate collected from diseased watermelon in central Taiwan (MYSV-TW) was found to react with a rabbit antiserum (RAs) prepared against the NP of Watermelon silver mottle virus (WSMoV), and a monoclonal antibody (MAb) prepared against the common epitope of the NSs proteins of WSMoV-serogroup tospoviruses, but not with the WSMoV NP-specific MAb, in both enzyme-linked immunosorbent assay (ELISA) and western blotting. In this investigation, both RAs and MAb against MYSV-TW NP were produced. Results of serological tests revealed that the RAs to MYSV-TW NP reacted with the homologous antigen and the crude antigens of members of the WSMoV serogroup, including members of the formal species WSMoV and Peanut bud necrosis virus, and members of three tentative species, Watermelon bud necrosis virus, Capsicum chlorosis virus and Calla lily chlorotic spot virus. The MAb to MYSV-TW NP reacted only with the homologous antigen and the other geographic isolates of MYSV from Japan (JP) and Thailand (TH). Our results of reciprocal tests indicate that the NP and the NSs protein of MYSV are serologically related to those of WSMoV-serogroup tospoviruses. Furthermore, we show that both the MYSV NP MAb and the WSMoV NP MAb are reliable tools for identification of MYSV and WSMoV from single or mixed infection in field surveys, as verified using species-specific primers in reverse transcription-polymerase chain reaction.

Calla lily chlorotic spot virus (CCSV) collected from calla lily plants showing symptoms in Taiwan has been identified as a tentative species of the genus Tospovirus based on the comparison of S RNA sequences. In this investigation, the complete sequences of its L and M RNAs were determined. The L RNA contains 8911 nucleotides (nt) and encodes a putative RNAdependent RNA polymerase of 2882 amino acids (aa) (332 kDa) in the viral complementary (vc) sense. The M RNA was shown to be 4704 nt in length, encoding a nonstructural NSm protein of 309 aa (35 kDa) in the viral sense and a Gn ⁄ Gc glycoprotein precursor (GP) of 1123 aa (128 kDa) in the vc sense. Phylogenetic analysis of the individual tospoviral proteins indicated that CCSV is closely related to Tomato zonate spot virus, a new tentative tospovirus isolated from tomato in southern China. Two degenerate primer pairs gL2740 ⁄ gL3920c and gM410 ⁄ gM870c, designed, after sequence comparison, from the highly conserved regions of the L and NSm genes, respectively, were successfully used to detect 12 greenhouse-cultured tospoviruses, including six formal species and six tentative species, by reverse transcription-polymerase chain reaction. They were also used to detect Melon yellow spot virus and Watermelon silver mottle virus from field cucurbit samples in Taiwan. The results indicate that the two degenerate primer pairs can be used for prompt detection of most tospoviruses and exploration of unknown tospovirus species.

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Chilli pepper (Capsicum annuum L.) is one of the most important crops in Yunnan Province, China. An orthotospovirus isolate 14YV855 was isolated from a diseased chilli pepper plant exhibiting yellow ringspots and necrosis on leaves in Shiping County, Honghe Hani and Yi Autonomous Prefecture, Yunnan Province in 2014. The complete genome sequence of 14YV855 was determined. The small, medium, and large RNAs are 3,428, 4,781, and 8,917 nucleotides long, respectively. The complete nucleocapsid (N) protein of 14YV855 shares a high amino acid identity of 84.8 to 89.9% to that of Capsicum chlorosis virus (CaCV), Groundnut bud necrosis virus (GBNV), Watermelon bud necrosis virus (WBNV), and Watermelon silver mottle virus (WSMoV), which is slightly less than the 90% identity threshold for the demarcation of new Orthotospovirus sp. Phylogenetic analyses revealed that the N protein and RNA-dependent RNA polymerase of 14YV855 are the most related to WSMoV, while the NSs, NSm, and Gn/Gc proteins are similar to those of GBNV. As expected, 14YV855 is serologically related to CaCV, GBNV, WBNV, and WSMoV when the monoclonal antibody against the N protein of WSMoV was used; however, 14YV855 can be distinguished from other orthotospoviruses by reverse-transcription PCR using the specific primers. Our results indicate that 14YV855 is a new Orthotospovirus sp. belonging to the WSMoV serogroup and is provisionally named Chilli yellow ringspot virus.