First report of cucurbit chlorotic yellows virus infecting cucumber in South Korea

Authors: KWAK, H.-R - Korean Rural Development Administration; BYUN, H.-S - Korean Rural Development Administration; CHOI, H.-S - Korean Rural Development Administration; HAN, J.-W. - Chungcheongnam-Do Agricultural Research And Extension Services; KIM, C.-S - Korean Rural Development Administration; Wintermantel, William - Bill; KIM, J.-E - Chungbuk National University; KIM, MIKYEONG - Chungbuk National University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2021
Publication Date: 4/22/2021
Citation: Kwak, H.-R., Byun, H.-S., Choi, H.-S., Han, J.-W., Kim, C.-S., Wintermantel, W.M., Kim, J.-E., Kim, M. 2021. First report of cucurbit chlorotic yellows virus infecting cucumber in South Korea. Plant Disease. https://doi.org/10.1094/PDIS-10-20-2254-PDN.
DOI: https://doi.org/10.1094/PDIS-10-20-2254-PDN

Interpretive Summary: In October 2018, cucumber plants showing yellowing and chlorotic mottle symptoms were observed in a greenhouse in Chungbuk, South Korea. The observed symptoms were similar to those caused by cucurbit aphid-borne yellows virus (CABYV), which has been detected on cucumber plants in the region since it was reported on melon in Korea in 2015. To identify the potential agents causing these symptoms, 28 samples from symptomatic leaves and fruit of cucumber plants were for infection by CABYV using RT-PCR. CABYV was detected in 17 of the 28 samples, while 11 symptomatic samples tested negative. In order to identify the cause of the symptoms, RT-PCR was performed using primers specific to cucurbit chlorotic yellows virus (CCYV) and cucurbit yellow stunting disorder virus (CYSDV). Eight of 28 samples were positive for CCYV; seven samples were infected with only CCYV and 1 contained a mixed infection of CABYV and CCYV. CYSDV was not detected in any sample. This study documents the first report of CCYV in Korea. CCYV has the potential to become a serious threat to production of cucurbit crops in Korea, particularly due to the increasing prevalence of the whitefly, Bemisia tabaci, in greenhouse production in Korea. It will be important to continue monitoring for CCYV and determine potential alternate hosts in the region to manage and prevent further spread of CCYV in Korea.

Technical Abstract: In October 2018, cucumber plants showing yellowing and chlorotic mottle symptoms were observed in a greenhouse in Chungbuk, South Korea. The observed symptoms were similar to those caused by cucurbit aphid-borne yellows virus (CABYV), which has been detected on cucumber plants in the region since it was reported on melon in Korea in 2015. To identify the potential agents causing these symptoms, 28 samples from symptomatic leaves and fruit of cucumber plants were subjected to total RNA extraction and RT-PCR was performed on total RNA using CABYV specific primers. CABYV was detected in 17 of the 28 samples, while 11 symptomatic samples tested negative. In order to identify the cause of the symptoms, RT-PCR was performed using cucurbit chlorotic yellows virus (CCYV) and cucurbit yellow stunting disorder virus (CYSDV) specific primers. Eight of 28 samples were positive using the CCYV specific primers; seven samples were infected with only CCYV and 1 contained a mixed infection of CABYV with CCYV. CYSDV was not detected in any sample tested. The expected 373 nt amplicons were bi-directionally sequenced, and BLASTn analysis showed that the nucleotide sequences shared 98 to 100% identity with CCYV isolates from East Asia, including NC0180174 from Japan. Two pairs of primers for amplification of the complete coat protein and RNA-dependent RNA polymerase (RdRp) genes were used to amplify the 752bp coat protein and 1514bp RdRp genes, respectively, which were cloned into the pGEM T- Easy vector and sequenced (Genbank accession nos. MW033300, MW033301). The CP and RdRp sequences demonstrated 99% nucleotide and 100% amino acid identity with the respective genes and proteins of the CCYV isolates from Japan. This study documents the first report of CCYV in Korea. CCYV has the potential to become a serious threat to production of cucurbit crops in Korea, particularly due to the increasing prevalence of the whitefly, Bemisia tabaci, in greenhouse production in Korea. It will be important to continue monitoring for CCYV and determine potential alternate hosts in the region to manage and prevent further spread of CCYV in Korea.