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Korean ginseng (Panax ginseng) is a dicotyledonous, medicinal, perennial plant belonging to the genus Panax of the family Araliaceae. We investigated the occurrence and incidence of plant viruses in Panax ginseng in Korea. A total of 656 leaf samples were combined into one and total RNA was extracted from the polled sample, using RNA sequencing (RNA-Seq), a metatranscriptome analysis of the plant virome was conducted. The virus present in Panax ginseng was confirmed by reverse transcription polymerase chain reaction (RT-PCR) assay using virus-specific primers. In RNA-Seq data analysis, the multiplication protein of four viral contigs including Aristotelia chilensis virus 1 (AcV1), Turnip mosaic virus (TuMV), Watermelon mosaic virus (WMV), and Tobamovirus multiplication protein were discovered. From our metatranscriptome analysis and RT-PCR assay, TuMV and WMV were detected, whereas the three viruses reported in China such as tomato yellow leaf curl China virus; panax notoginseng virus A; and panax virus Y were not found in this study. The distribution of domestic ginseng viruses seems different from that recorded in China. Overall, this is the first plant virome analysis of Panax ginseng in Korea.

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The Cnidium officinale plant, which belongs to the Apiaceae family, has been widely used as a side dish and a traditional medicine to treat a variety of diseases in South Korea as well as other East Asian countries (Kumar et al. 2013). Recently, two distinct viruses, cnidium vein yellowing virus -1(CnVYV-1) and CnVYV-2 (family Secoviridae) (Yoo et al. 2015) and cnidium virus X (family Alphaflexiviridae) (Honma et al. 2019) have been reported in C. officinale in South Korea and Japan, respectively. In May 2018, 43 individual C. officinale plants showing symptoms of leaf mosaic, vein clearing and mild mottling were observed in the garden of the National Institute of Forest Science in Seoul, South Korea. Total RNA was extracted from a pool of 43 samples using the easy-spin total RNA extraction kit (iNtRON Biotechnology, Inc., South Korea), and ribosomal RNA was removed using Ribo-ZeroTM rRNA Removal Kits (Plant Leaf) (Epicentre, Madison, WI, USA) before complementary DNA library construction. Library was generated using an Illumina TruSeq RNA sample prep kit (Illumina, San Diego, CA, USA) and sequencing performed by the Illumina HiSeq4000 system at Macrogen (Daejeon, Korea). In total, 97,718,248 high quality reads were obtained after trimming, which were assembled into 75,798 contigs. The contigs were analyzed using the BLASTn and BLASTx searches to identify sequences in the high throughput sequencing (HTS) data similar to the reference genome sequences in the GenBank which showed that the C. officinale plants were infected with several previously known plant viruses, including CnVYV-1, CnVYV-2 and cucumber mosaic virus. In addition, we identified 12 contigs with lengths of 238 to 4,180 bp which showed query coverage of 94 to 100% and 79.71 to 89.07% nucleotide (nt) identities with RNA1 and RNA2 segments of CNSV isolates in the GenBank database. To further confirm HTS data and detect the presence of CNSV, reverse transcription-polymerase chain reaction (RT-PCR) was performed using virus-specific primer sets of CNSV RNA1 (F1: 5'-AATGCTTATGTTTTCGGAGAAAGAG-3', R1: 5'- GTTGGTACATATGGGTCCAATC-3') and of CNSV RNA2 (F2: 5'-GTGCCGCACTATTAATTTTACTC-3', R2: 5'-ATTTTTCCCTTTTGGTGTAGTGAA-3') (Supplementary Table 1). The expected size RT-PCR fragments, 1,334 bp and 442 bp were amplified from RNA extracted from one C. officinale sample (#7) with vein clearing symptom out of the 43 samples tested (Supplementary Fig 1). The RT-PCR products were directly sequenced by Sanger sequencing and the partial sequences of the amplicons corresponding to CNSV RNA-1 and RNA-2 have been deposited at the GenBank database under the accession numbers MN905738 and MN905739, respectively. BLASTn analysis demonstrated that RT-PCR products shared 86.80% (RNA1) and 84.20% (RNA2) nt identities with CNSV RNA1 (GenBank accession: BK010916) and RNA2 (GenBank accession: BK010917), respectively. The cycas necrotic stunt virus (CNSV), a member of the genus Nepovirus in the family Secoviridae, was first detected in cycas (Cycas revoluta) in Japan (Kusunoki et al. 1986). CNSV has been detected in other hosts and geographical areas (Jiang et al. 2019). To our knowledge, this is the first report of CNSV infecting C. officinale in South Korea. Further research is needed to understand the transmission, epidemiology and pathological properties of the virus. References Kumar, H., et al. 2013. Molecules 18: 14670-14693. doi: 10.3390/molecules181214670 Honma, H., et al. 2019. Arch. Virol. 164:1931-1935. doi: 10.1007/s00705-019-04261-6. Jiang,P., et al.2019. Microbiol Resour. Announc. 8. pii: e00981-19. doi: 10.1128/MRA.00981-19. Kusunoki, M., et al. 1986. Ann Phytopath Soc Japan 52: 302-311. doi:org/10.3186/jjphytopath.52.422 Yoo R.H., et al. 2015. Arch. Virol. 160:2911-4. doi: 10.1007/s00705-015-2557-1 Compliance with Ethical Standards Conflicts of interest: The authors declare that they have no conflicts of interest. Ethical approval: This article does not contain any studies with human participants or animals performed by any of the authors.