Emergence of watermelon chlorotic stunt virus in melon and watermelon in the southwestern United States

Authors: Wintermantel, William; TIAN, TONGYAN - California Department Of Food And Agriculture; Chen, Carol; WINARTO, NICHOLAS - California Department Of Food And Agriculture; SZUMSKI, SHELLY - California Department Of Food And Agriculture; Hladky, Laura; GURUNG, SURAJ - Sakata Seed America, Inc; PALUMBO, JOHN - University Of Arizona

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2024
Publication Date: 11/12/2024
Citation: Wintermantel, W.M., Tian, T., Chen, C., Winarto, N., Szumski, S., Hladky, L.L., Gurung, S., Palumbo, J.C. 2024. Emergence of watermelon chlorotic stunt virus in melon and watermelon in the southwestern United States. Plant Disease. 108(12):3664. https://doi.org/10.1094/PDIS-05-24-1009-PDN.
DOI: https://doi.org/10.1094/PDIS-05-24-1009-PDN

Interpretive Summary: Watermelon and melon plants with leaves exhibiting mosaic symptoms or chlorotic spotting with limited leaf distortion were observed in commercial fields throughout Yuma County, AZ, and Imperial County, CA, in fall 2023. Older leaves, particularly in melon, also exhibited yellowing typical of infection by whitefly-transmitted viruses common in the region, and sweetpotato whiteflies were prevalent in fields. Plants were tested for the presence of known viruses, as well as for a type of virus that often induces symptoms similar to those observed. Results identified the presence of a new virus, watermelon chlorotic stunt virus (WmCSV), which was confirmed throughout Yuma and Imperial Counties by sequencing of the virus genome and molecular testing methods. This is the first report of WmCSV infecting cucurbits in the United States. Interestingly, nearly all melon and some watermelon plants infected with WmCSV were co-infected with cucurbit yellow stunting disorder virus. Research is in progress to determine the potential impact of WmCSV on the cucurbit virus complex in the Sonoran Desert and the U.S. as a whole, and to understand the epidemiological factors that influence WmCSV infection and spread.

Technical Abstract: Watermelon (Citrullus lanatus) and melon (Cucumis melo) plants with leaves exhibiting mosaic symptoms or chlorotic spotting, respectively, along with limited foliar distortion, predominantly on newer growth, were observed in commercial fields throughout Yuma County, AZ, and Imperial County, CA, in fall 2023. Older leaves, particularly in melon, also exhibited yellowing typical of infection by whitefly-transmitted viruses common in the region, and whiteflies (Bemisia tabaci) were prevalent in fields. Symptomatic plants were tested using a multiplex RT-PCR for cucurbit yellow stunting disorder virus (CYSDV), cucurbit chlorotic yellows virus (CCYV), squash vein yellowing virus (SqVYV), and cucurbit aphid-borne yellows virus (CABYV), and separately for cucurbit leaf crumple virus (CuLCrV). Most plants were infected with CYSDV, but unusual symptoms on newer growth suggested the possibility of infection by a begomovirus. Rolling circle amplification and DNA sequencing of nucleic acid extract from a symptomatic melon plant collected in Dome Valley, AZ, identified the presence of watermelon chlorotic stunt virus (WmCSV), a bipartite begomovirus (Geminiviridae), but no other begomoviruses. Sequencing of the complete genome determined that DNA A shared 99% identity with WmCSV isolates from cactus and melon in Sonora, Mexico, and DNA B shared 96% and 94% identity with WmCSV isolates from watermelon in Palestine and Sonora, respectively. PCR targeting both WmCSV DNA A and B was used for secondary confirmation, and confirmed WmCSV infection. PCR using the DNA A or B primers confirmed the presence of WmCSV from additional watermelon and melon samples collected from Yuma and Imperial Counties. This is the first report of WmCSV infecting cucurbits in the United States. Interestingly, nearly all melon and some watermelon plants infected with WmCSV were co-infected with CYSDV but not by other whitefly-transmitted viruses. Most fall cucurbits in the Sonoran Desert production region become infected with CYSDV, and many are also infected with CCYV, SqVYV, or other viruses. However, incidence of CCYV and SqVYV in the region was extremely low during fall 2023. Research is in progress to determine the potential impact of WmCSV on the cucurbit virus complex in the Sonoran Desert and the United States as a whole, and to understand the epidemiological factors that influence WmCSV infection and spread.