First report of Cucurbit chlorotic yellows virus infecting Cucumis melo (muskmelon and oriental melon) in Korea

Authors: CHO, IN-SOOK - Rural Development Administration - Korea; KIM, TAE-BOK - Rural Development Administration - Korea; YOON, JU-YEON - Rural Development Administration - Korea; CHUNG, BONG-NAM - Rural Development Administration - Korea; Hammond, John; LIM, HYOUN-SUB - Chungnam National University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2021
Publication Date: 2/2/2021
Citation: Cho, I., Kim, T., Yoon, J., Chung, B., Hammond, J., Lim, H. 2021. First report of Cucurbit chlorotic yellows virus infecting Cucumis melo (muskmelon and oriental melon) in Korea. Plant Disease. https://doi.org/10.1094/PDIS-11-20-2375-PDN.
DOI: https://doi.org/10.1094/PDIS-11-20-2375-PDN

Interpretive Summary: Virus infections in crops can reduce yield and quality of the crop. Many of these viruses are transmitted by insect vectors such as whiteflies, which are difficult to control in greenhouse or field conditions. The whitefly-transmitted cucurbit chlorotic yellowing virus (CCYV) was first reported in Japan, and has since been reported in other parts of Asia, Europe, parts of Africa, and in the USA; however, CCYV had not been identified in Korea. Scientists in Korea observed a few plants of muskmelon growing in a greenhouse in 2018 with foliar yellowing and vein clearing symptoms. They identified the causal agent as CCYV, and subsequently observed levels of 80-90% incidence of similar symptoms in greenhouse crops of muskmelon and oriental melon in the summer of 2020. CCYV was confirmed from all of the symptomatic samples tested, with no findings of three other whitefly-transmitted viruses known to cause similar symptoms. CCYV appears to now be established in Korea and could represent a serious threat of yield losses to cucurbit crops in Korea. It is important to control vector populations to prevent spread of CCYV in the field.

Technical Abstract: In December 2018, leaves showing virus-like symptoms of yellowing and vein clearing were observed on 2% of muskmelon (Cucumis melo L.) plants grown under plastic houses in Gyeongsang province, Korea. Total RNA from a sample of leaves from two plants was extracted using RNeasy Plant Mini Kit (Qiagen, Germany) and subjected to high throughput sequencing. After pre-processing and Ribo-Zero rRNA removal, a cDNA library was prepared using an Illumina TruSeq Stranded Total RNA kit and sequenced on an Illumina NovaSeq 6000 system (Macrogen Inc. Korea). De novo assembly of the 88,222,684 reads was performed using Trinity software (r20140717); the initially assembled 146,269 contigs were screened against the NCBI viral genome database using BLASTN. By these means, two contigs derived from cucurbit chlorotic yellows virus (CCYV) reported to cause yellowing disorder were identified. Contigs with lengths of 8,539 and 8,040 nt shared highest nt identities of 99.89 and 99.91% with segment RNA1 and RNA2 of two distinct CCYV isolates (GenBank JN641883 and MH819191, respectively). CCYV was first reported from Japan (Okuda et al., 2010), and soon after from Taiwan and China (Huang et al., 2010; Gu et al., 2011); the ten sequences most closely-related to each RNA of the Korean isolate (=99% coverage and =99.60% nt identity) were from Japan, China, or Taiwan, except for isolate IL from Israel. To confirm CCYV infection, reverse transcription-polymerase chain reaction (RT-PCR) was performed using virus-specific primers, RdRp-F/RdRp-R (5’-ACCGAACACTTGGCTATCCAA-3’/5’-CTTAATGCCGCGTATGAACTCA-3’) and HSP-F/HSP-R (5’-TGAACGACACTGAGTTCATTCCTA-3’/5’-CGCCAAGATCGTACATGAGGAA-3’) designed based on the contig sequences of the RNA dependent RNA polymerase (RdRp) region of RNA1 and the heat shock protein 70 homolog (HSP70h) region of RNA2, respectively. RT-PCR products of the expected 450 bp and 510 bp were obtained from the two symptomatic samples and two asymptomatic samples were negative. Amplicons were cloned into the pGEM-T Easy Vector (Promega, USA) and two clones for each amplicon were bidirectionally sequenced (BIONEER, Korea). The sequence was deposited in NCBI GenBank (accession no. LC592226 and LC592227) showed 100% and 99.22% nt identity with the corresponding sequences of RdRp and HSP70h gene of Chinese isolate SD (MH819190 and MH819191) and others, respectively. Other cucurbit-infecting criniviruses: beet pseudo-yellows virus (BPYV), cucurbit yellow stunting disorder virus (CYSDV) and cucurbit aphid-borne yellows virus (CABYV) were not detected in the samples. In June and September 2020, muskmelon and oriental melon (Cucumis melo L. var. makuwa) plant showing yellowing disease incidence of 80 to 90% were observed in Gyeonggi and Jeolla provinces, respectively. Whiteflies were observed in all investigated plastic houses. Symptomatic leaf samples (muskmelon, 14; oriental melon, 6) were collected and tested by RT-PCR. Of 20 symptomatic samples, 19 were positive for CCYV, while BPYV, CYSDV and CABYV were not detected. The sequence (LC592230) showed 100% nt identity with the corresponding sequence of HSP70h from China (MH819191). To our knowledge, this is the first report of CCYV infecting muskmelon and oriental melon in Korea. Whitefly-transmitted CCYV could represent a serious threat of yield losses to cucurbit crops in Korea. It is important to control vector populations to prevent spread of CCYV in the field.