Characterization of Calla lily chlorotic spot virus as a new tospovirus species
Yeh S-D1, Chen T-C1, Lin Y-H1, Hsu H-T2, Chen C-C3
1Department of Plant Pathology, National Chung Hsing University, Taichung, 40227, Taiwan.
2US Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Beltsville, MD20705, USA
3Taichung District Agricultural Improvement Station, Changhua, 515, Taiwan
Correspondence: sdyeh@nchu.edu.tw
A new tospovirus designated Calla lily chlorotic spot virus (CCSV) that caused chlorotic spots ranging from light green to yellow on the middle leaves of the affected calla lilies was isolated from central Taiwan. Virions of 75 to 105 nm in diameter were found present in crude extracts and ultra thin sections of diseased leaves by electron microscopy, and the transmission by Thrips palmi was evidenced. Polyclonal and monoclonal antibodies (MAbs) to the nucleocapsid protein (NP) of CCSV were produced. Weak cross-reaction was observed when the rabbit antiserum to the CCSV or Watermelon silver mottle virus (WSMoV) NP was used to react with the heterologous antigen in indirect enzyme-linked immunosorbent assay (ELISA) and immunoblotting. On the contrary, MAbs produced to CCSV NP or WSMoV NP reacted specifically with the homologous antigen but not with the heterologous antigen in both ELISA and immunoblot analyses. Results of reverse transcription-polymerase chain reaction (RT-PCR) showed that the conserved regions of the L genes of tospoviruses are present in CCSV, but primers specific to the N gene of WSMoV failed to amplify DNA fragments from total RNA extracts of CCSV-infected plants. The CCSV S RNA was determined to be 3,172 nts in length, with an inverted repeat at 5' and 3' ends and two open reading frames encoding the NP and a non-structural (NSs) protein in an ambisense arrangement. A typical 3'-terminal sequence (5'-AUUGCUCU-3') shared by all members of the genus Tospovirus was also noticed. Sequence analysis indicated that the CCSV NP and NSs protein share low amino acid identities, 20.1 to 65.1% and 19.9 to 66.1%, respectively, with those of reported tospoviruses. Phylogenetic dendrogram analysis indicated that CCSV is a distinct member in the genus Tospovirus. We conclude that CCSV is a new tospovirus species belonging to the WSMoV serogroup.
