First report of Cucumber mosaic virus in Farfugium japonicum in Korea

Farfugium japonicum is a species of flowering plant of the family Asteraceae, also known as leopard plant or green leopard plant. It is native to streams and seashore of Korea, and the plant species has become an ornamental garden plant in East Asia as well as Europe. During April 2015, virus-like foliar symptoms, including a mosaic with dark green islands surrounding the veins, were observed on leopard plants in a garden located on Jeju island, Korea. To identify a causal virus, five symptomatic leaf samples were analyzed by transmission electron microscopy (TEM) of leaf dip preparations. Icosahedral virus particles (~30 nm in length) were observed from all test leaf samples. Then, the symptomatic leaf samples were analyzed using lateral flow immunoassay for some plant viruses developed by our laboratory and a commercial company (Agdia, Elkhart, U.S.A.). 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 (called CMV-RIGS kit). The presence of CMV was also confirmed by serological detection with a commercially available DAS-ELISA kit. The virus (named CMV-Leo) caused necrotic local lesions on Chenopodium amaranticolor at 5 days post-inoculation (dpi), while mild to severe mosaic was observed in Nicotiana glutinosa, N. tabacum ‘Samsun NN,’ Cucurbita pepo ‘Super-Top,’ Cucumis sativus, Capsicum annuum, Physalis angulate, Raphanus sativus, and Solanum lycopersicum ‘Unicorn’ 10 to 14 dpi. To verify whether CMV-Leo was the cause of disease symptoms observed in leopard plants, five virus-free leopard plants were mechanically inoculated by sap from symptomatic tobacco leaves infected with CMV-Leo. At 6 weeks after inoculation, all plants produced systemic mosaic symptoms, resulting in positive reactions for CMV using a lateral flow immunoassay kit specific to CMV, whereas mock-inoculated leopard plants remained symptomless and virus-free. The presence of CMV-Leo in all naturally infected and mechanically inoculated plants was further verified by RT-PCR (Han et al. 2012). Multiple alignment of the CMV-Leo CP sequence (accession no. LC169487) with CP sequences of other CMV isolates using MEGA6.0 software revealed 96.8 to 99.1% and 71.0 to 73.0% identities to those of CMV subgroup I and subgroup II, respectively. These results provide additional confirmation of CMV-Leo infection. Being perennial, leopard plants could serve as a reservoir for CMV to infect other ornamentals and cultivated crops (Palukaitis and Garcia-Árenal 2003). To our knowledge, this is the first report of CMV infection in the leopard plant species in the world.