Detection of Cucurbit Yellow Stunting Disorder Virus Infecting Watermelon in South Carolina

Watermelon is an important cucurbit crop grown in 44 states in the United States of America (USA). South Carolina (SC) had the seventh largest watermelon production area in USA with 4,500 acres in 2018 valued at approximately $17 million. In June 2019, four watermelon plants displaying symptoms of virus infection including stunting, leaf crumpling, interveinal chlorosis, and necrosis of leaf margins were observed in a research trial in Charleston, SC. Whiteflies were observed on the abaxial surface of the leaves. One plant was tested for the presence of whitefly-transmitted cucurbit leaf crumple virus (CuLCrV), cucurbit yellow stunting disorder virus (CYSDV), and squash vein yellowing virus and aphid-transmitted papaya ringspot virus by RT-PCR. Amplicons of the expected size were only observed for CuLCrV (∼1 kb) and CYSDV (∼0.7 kb). Because CYSDV was not previously reported from SC, we continued to monitor the field for virus symptoms during the summer season. By mid-August 2019, 15 additional plants (1.9% incidence) were observed with similar symptoms of virus infection. Two virus identification methods (CP and Hsp70h) confirmed that CYSDV was indeed present in watermelon samples in SC. The geographic range of CYSDV and other whitefly-transmitted viruses continues to expand into and within major cucurbit-producing regions with each production season, especially in the southeastern USA. This is the first report of CYSDV infecting watermelon or any other plant in SC. These three whitefly-transmitted viruses now need to be considered in management plans by SC growers. Knowledge of the presence of CYSDV, an additional virus, infecting cucurbits, in SC is also important from a regulatory perspective.