First Report of Cotton Leafroll Dwarf Virus Infecting Hibiscus syriacus in South Korea (2022)

Three cotton leafroll dwarf virus (CLRDV; genus Polerovirus, family Solemoviridae) genotypes have recently been identified (Tabassum et al., 2021; Ramos-Sobrinho et al., 2021). This virus is widespread in the United States (Thiessen et al., 2020; Aboughanem-Sabanadzovic et al., 2019; Tabassum et al., 2020) and has also been reported to infect chickpea (Cicer arietinum) in Uzbekistan (Kumari et al., 2020). As well, CLRDV was detected from 23 weed species (16 families), including Hibiscus sabdariffa (Sedhain et al., 2021, Hagan et al., 2019). From June to September 2019, virus-like symptoms, including mild leaf stunting, crinkling, and deformation, were observed in multiple plants (n=14) in several provinces of South Korea (e-Xtra Table. 1). To characterize the associated viruses, pooled leaf tissues from all 14 samples were used for total RNA isolation, followed by paired-end high-throughput sequencing (HTS) on the Illumina NovaSeq 6000 platform (Macrogen, South Korea). A total of 614,424,952 trimmed and high-quality reads were assembled into 506,024 contigs using Trinity de novo transcriptome assembly. The resulting contigs were compared with viral sequences in the GenBank database using BLASTx analysis. Several viral contigs were identified, including cucumber mosaic virus, apple stem pitting virus, apple stem grooving virus, cherry virus A, and CLRDV. The CLRDV contig of 5,800 nucleotides (nt) with an average coverage of 307x shared 92.1% identity (query coverage: 99%) with the CLRDV isolate CN-S5 (KX588248). To confirm CLRDV infection and to obtain its complete genome sequence, total RNA was extracted from each of the 14 samples and used for reverse transcription (RT)-PCR with six overlapping sets of primers designed from the HTS contig (e-Xtra Table. 2). The expected product sizes were obtained only for the Hibiscus syriacus L. (family: Malvaceae) sample showing foliar mild vein clearing symptoms on the leaves (e-Xtra Fig.1). All RT-PCR products were cloned using the RBC TA Cloning vector (Taipei, Taiwan) and at least five positive clones per cloned DNA fragment were sequenced. The 5 and 3 termini sequences were determined as described previously (Zhao et al. 2016). The complete genome of CLRDV isolate SK (OK073299) was determined to be 5,862 nt and it shared 89-91% complete genome identity with 12 other CLRDV isolates based on pairwise comparisons (e-Xtra Table. 3). Maximum likelihood phylogenetic analysis based on the complete genome and P3-CP aa sequences showed that CLRDV-SK is more closely related CN-S5 (e-Xtra Fig. 2). In the fall of 2021, additional H. syriacus samples (n=18) with mild chlorosis, blistering and crinkling symptoms were collected from 2 provinces of South Korea and tested by RT-PCR using the primers: CLRDV-SK-101-120 For & CLRDV-SK-1021-1040 Rev targeting a region of the ORF0. Two of 18 samples (11.1%) tested positive for CLRDV. The 16 negative samples only showed symptoms of mild yellowing. The RT-PCR products were cloned and sequenced. In pairwise comparisons, the obtained sequences (OM339522-23) were 95.85% and 96.06% identical to the corresponding sequences of CLRDV isolate SK. This is the first report of CLRDV occurrence in H. syriacus in South Korea to the best of our knowledge. Our findings will assist further studies on the epidemiology and sustainable management of diseases caused by CLRDV. Acknowledgments This work was supported by IPET (Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries; Project No. AGC1762111), Ministry of Agriculture, Food and Rural Affairs, Republic of Korea. References Tabassum, A., et al., 2021. PloS One. 16: e0252523 Ramos-Sobrinho, R., et al., 2021. Viruses. 13:2230 Thiessen, L.D., et al. 2020. Plant Dis. 104:3275 Aboughanem-Sabanadzovic, N., et al. 2019. Plant Dis. 103:1798 Tabassum, A., et al. 2020. Microbiol. Res. Announce. 9:e00812-20 Kumari, S.G., et al. 2021. Plant Dis. 104:2532 Sedhain, N.P., et al. 2021. Crop protection 144:105604 Hagan, A., er al. 2019. Alabama Cooperative Extension System. ANR:2539 Zhao, F., et al. 2016. Arch. Virol. 161:2047 Conflict of interest The authors declare that they have no conflict of interest.