Nanopore Sequencing Reveals the First Report of Poinsettia Mosaic Virus Infecting Euphorbia milii in South Korea

The poinsettia mosaic virus (PnMV) was first identified in Euphorbia milii in South Korea using nanopore sequencing; the complete genome of this isolate, named PnMV-CNU, has subsequently been assembled and characterised. The transcriptomic analysis results were further validated by RT-PCR using PnMV-specific primers and Sanger sequencing. The PnMV-CNU genome consisted of 6094 nucleotides, encoding a polyprotein with conserved domains typical of the Tymoviridae family, including methyltransferase, protease, helicase, RNA-dependent RNA polymerase and coat protein. Phylogenetic analysis demonstrated a close relationship between PnMV-CNU and other isolates, suggesting a broad geographical distribution of the virus. Mechanical inoculation of PnMV-CNU onto Chenopodium album confirmed its infectivity, resulting in systemic foliar necrosis on inoculated plants. To our knowledge, this study represents the first report of PnMV infecting E. milii, expanding the known host range of the virus and highlighting the importance of rapid diagnostic tools such as nanopore sequencing. These findings underscore the need for vigilant surveillance to mitigate the impact of PnMV on Euphorbia species.