Catharanthus roseus, commonly known as Madagascar rosy periwinkle (also called vinca), is a tropical perennial herb of the family Apocyanaceae. Periwinkle is a bedding plant widely used in Korea because of its drought tolerance, low maintenance, and varied flower colors. In May 2013, virus-like foliar symptoms, including a mosaic with malformation of leaves, were observed on a periwinkle plant in a greenhouse located in Chonbuk Province, Korea. Cucumber mosaic virus (CMV) was identified in the symptomatic plant by serological testing for the presence of CMV coat protein (CP) with an immune-strip kit developed by our laboratory. The presence of CMV was confirmed by serological detection with a commercially available double-antibody sandwich (DAS)-ELISA kit (Agdia, Elkhart, IN). Sap from the serologically positive sample was mechanically inoculated to test plants using 10 mM phosphate buffer (pH 7.0). The virus (named CMV-Vin) caused necrotic local lesions on Chenopodium amaranticolor at 5 days-post-inoculation (dpi), while mild to severe mosaic was observed in Capsicum annuum, Cucumis sativus, Cucurbita pepo ‘Cheonggobong,’ Nicotiana glutinosa, N. tabacum‘Samsun NN,’ Physalis angulate, and Solanum lycopersicum ‘Pink-Top’ 10 to 14 dpi. Examination of the inoculated plant leaves by DAS-ELISA and electron microscopy (leaf dips) showed positive reactions to CMV and the presence of spherical virions ~28 nm in diameter, respectively. To verify whether CMV was the causal agent for the disease symptoms observed in naturally infected periwinkle, virus-free periwinkle (10 plants) was mechanically inoculated by sap from local lesions on C. amaranticolor inoculated with CMV-Vin. At 6 weeks after inoculation, all plants produced systemic mosaic and distortion of leaves, resulting in strong DAS-ELISA reactions for CMV, whereas mock-inoculated periwinkle plants remained symptomless and virus-free. The presence of CMV-Vin in all naturally infected and mechanically inoculated plants was further verified by reverse transcription (RT)-PCR. Total RNAs were extracted with a RNeasy Plant Mini Kit (Qiagen, Valencia, CA) and RT-PCR was carried out with the One-Step RT-PCR Kit (Invitrogen, Carlsbad, CA) using a pair of primers, CMVCPFor and CMVCPRev (1), which amplified the entire CP gene. RT-PCR products (657 bp) were obtained from all naturally infected and mechanically inoculated plants as well as from a positive control (viral RNAs from virions), but not from healthy tissues. The amplified RT-PCR products were directly sequenced using BigDye Termination kit (Applied Biosystems, Foster City, CA). Multiple alignment of the CMV-Vin CP sequence (Accession No. AB910598) with CP sequences of other CMV isolates using MEGA5 software revealed that 91.8 to 99.0% and 71.0 to 73.0% identities to those of CMV subgroup I and subgroup II, respectively. These results provide additional confirmation of CMV-Vin infection. Being perennial, periwinkle plants could serve as a reservoir for CMV to infect other ornamentals and cultivated crops (2). To our knowledge, this is the first report of CMV infection on periwinkle in Korea.
References: (1) S. K. Choi et al. Virus Res. 158:271, 2011. (2) P. Palukaitis et al. Adv. Virus. Res. 41:281, 1992.
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