Biological, Pathological, and Molecular Characteristics of a New Potyvirus, Dendrobium Chlorotic Mosaic Virus, Infecting Dendrobium Orchid

Dendrobium smillieae is one of the popular orchids in Taiwan. This report describes a new potyvirus tentatively named Dendrobium chlorotic mosaic virus (DeCMV) causing chlorotic and mosaic symptoms in D. smillieae. Enzyme-linked immunosorbent assay (ELISA) tests using six antisera against orchid-infecting viruses revealed that only a monoclonal antibody against the potyvirus group reacted positively with crude saps prepared from a symptomatic dendrobium orchid. Potyvirus-like, flexuous, filamentous particles were observed under an electron microscope, measuring approximately 700 to 800 nm in length and 11 to 12 nm in diameter. Sequence analyses revealed that DeCMV coat protein gene shared 59.6 to 66.0% nucleotide sequence identity and 57.6 to 66.0% amino acid sequence identity, whereas the DeCMV complete genome shared 54.1 to 57.3% nucleotide sequence identity and 43.7 to 49.5% amino acid sequence identity with those other known potyviruses. These similarity levels were much lower than the criteria set for species demarcation in potyviruses. Thus, DeCMV can be considered a new potyvirus. The whole DeCMV genome contains 10,041 nucleotides (GenBank accession no. MK241979) and encodes a poly-protein that is predicted to produce 10 proteins by proteolytic cleavage. In a pathogenicity test, results of inoculation assays demonstrated that DeCMV can be transmitted to dendrobium orchids by grafting and mechanical inoculation, as verified by ELISA and western blot analyses using the DeCMV polyclonal antiserum and by reverse transcription polymerase chain reaction using the coat protein gene-specific primers. The inoculated orchids developed similar chlorotic and mosaic symptoms. In conclusion, DeCMV is a novel orchid-infecting potyvirus, and this is the first report of a new potyvirus that infects dendrobium orchids in Taiwan.