First report of pepper mild mottle virus ( Tobamovirus capsici ) infecting figwort ( Scrophularia buergeriana ) in Korea

Figwort (Scrophularia buergeriana) is a perennial herb of the family Scrophulariaceae, naturally occurring in moist mountainous areas and cultivated as a medicinal plant in Korea. It is traditionally used as a febrifuge and distributed mainly in northern Gangwon Province, Korea. Viruses previously reported to infect Scrophularia spp. include figwort mosaic virus (Shepherd, R. J., et al. 1987), scrophularia mottle virus (Rana, G. L., M. A. Castellano, and R. Koenig. 1988) and beet western yellows virus confirmed in Korea (Jeon, S. G., et al. 2021). However, no other viral diseases of figwort have been documented. In August 2022, mosaic and yellowing symptoms were observed on two of 20 figwort plants collected from Taebaek, Gangwon province, Korea. Total RNA was extracted separatly from the two symptomatic plants using the RNeasy Mini Kit (QIAGEN, Germany) and pooled prior to high-throughput sequencing (HTS). HTS was performed on the NovaSeq 6000 platform (Macrogen, Seoul, South Korea) using the TruSeq Standard Total RNA with Ribo-Zero Plant Kit (Illumina, San Diego, USA). De novo assembly of 28,668,016 reads using Geneious Prime v2023.2.1 and BLAST analysis against the NCBI virus genome database revealed a 6,356-nt contig corresponding to a near-complete genome sequence (GenBank accession no. LC793741) showing 99% nucleotide identity with pepper mild mottle virus (PMMoV-Kr, AB126003). This isolate was designated PMMoV-Scr. RT-PCR using tobamovirus-degenerate primers (forward: GAY GGN GTB CCN GGN TGY GG, reverse: CAN GAV TBN ABC TGT AAT TGC TAT) targeting a portion of the replication-associated protein gene (nt 2538-3418) (Li et al. 2018) amplified the expected product from symptomatic samples, and sequencing confirmed 96.02% nucleotide sequence identity of the RT-PCR amplicon with PMMoV-Kr. The difference in nucleotide identity values likely reflects variation among genomic regions, as the HTS-derived sequence represents a near-complete genome whereas the RT-PCR product covers only a partial region of the replication-associated protein gene. Sap inoculation of PMMoV-Scr was conducted on Nicotiana benthamiana, N. tabacum cv. Xanthi nc, N. glutinosa, Capsicum annuum cv. Bukang, and Chenopodium quinoa. PMMoV infection in inoculated plants was confirmed by RT-PCR using the tobamovirus-degenerate primers. In N. benthamiana, mosaic symptoms developed on the upper leaves. N. tabacum cv. Xanthi nc and N. glutinosa developed a hypersensitive response (HR) consistent with resistance mediated by the N gene. C. annuum cv. Bukang remained symptomless but tested positive by RT-PCR, whereas C. quinoa developed necrotic local lesions. These results confirm that figwort is a natural host of PMMoV in Korea. Further studies are warranted to assess its epidemiological significance and impact on medicinal plant cultivation and virus transmission dynamics.