First Report of Cucurbit Aphid-Borne Yellows Virus on <i>Sicyos angulatus</i> in Korea

Bur cucumber (<i>Sicyos angulatus</i>), known as gasibak in Korea, is an invasive species that has spread widely since its introduction. In July 2024, populations were surveyed along riverbanks in five southeastern regions of South Korea (Andong, Daegu, Cheongsong, Chilgok, and Gunwi). Across these locations, approximately 5% of the plants displayed viral symptoms such as yellowing and mosaic. A total of 25 symptomatic and asymptomatic leaf samples were collected. To identify viral infections, RT-PCR was conducted to detect nine cucurbit viruses common in Korea (Kwak et al., 2018; Park et al., 2011): cucumber mosaic virus (CMV, <i>Cucumovirus CMV</i>), cucumber green mottle mosaic virus (CGMMV, <i>Tobamovirus viridimaculae</i>), cucurbit aphid-borne yellows virus (CABYV, <i>Polerovirus CABYV</i>), cucurbit chlorotic yellows virus (CCYV, unclassified genus <i>Crinivirus</i>), kyuri green mottle mosaic virus (KGMMV, <i>Tobamovirus kyuri</i>), melon necrotic spot virus (MNSV, <i>Gammacarmovirus melonis</i>), papaya ringspot virus (PRSV, <i>Potyvirus papayanuli</i>), watermelon mosaic virus (WMV, <i>P. citrulli</i>), and zucchini yellow mosaic virus (ZYMV, <i>P. cucurbitaflavitesselati</i>). WMV and WMV+CABYV were present in 16 and 6 samples, respectively, across four regions, with no viral infections detected in Andong. All positive samples were infected with WMV, with no CABYV alone and none of the other seven viruses were detected. WMV-infected samples primarily showed mosaic symptoms with irregular discoloration and mottling, while co-infected samples displayed more pronounced yellowing or chlorosis in addition to mosaic patterns. This suggests a specific association of CABYV with the yellowing symptoms, significantly contributing to chlorosis alongside WMV. The observed co-infection aligns with prior reports of WMV and CABYV in cucurbits, emphasizing the need for monitoring both viruses due to their combined impact on symptom severity and yield losses (Rabadán and Gómez, 2023). Asymptomatic samples tested negative for viral infections. To confirm the CABYV infection, cDNA synthesis was conducted on a CABYV-positive sample, followed by PCR with newly designed coat protein gene-specific primers (5'-GTCTCGTTACCAAGAGTCCA/CGACGAACTCACCATCAGC-3'). The resulting amplicon was cloned, sequenced, and submitted to GenBank (accession no. PQ303621.1). This CABYV sequence, designated as isolate Gasibak, showed 100% identity (600/600 bp) with five isolates (KR231962.1, KR231961.1, KR231959.1, KR231949.1, and KR231944.1) previously identified from Korean melons through a BLASTn search. This marks the first report of bur cucumber as a natural host of CABYV worldwide. CABYV belongs to the genus <i>Polerovirus</i> in the family <i>Solemoviridae</i> (Sõmera et al., 2021). Although not commonly found in Korea in the past, this virus has become increasingly prevalent, particularly in oriental melon crops. Recently, Korean authorities recognized that CABYV causes yellowing symptoms in various cucurbit crops, leading to economic damage. While WMV has been reported in bur cucumber (Park et al., 2020), details remain limited. Both WMV and CABYV are known to be transmitted by aphids, raising the possibility that bur cucumber may contribute to the spread of these viruses, particularly in areas near cucurbit crops. Previous studies have shown that bur cucumber can rapidly spread along riverbanks and into agricultural areas, potentially impacting nearby ecosystems and crops (Osawa et al., 2013).