First report of cucurbit yellow stunting disorder virus and cucurbit chlorotic yellows virus in melon in the Central Valley of California

Authors: MONDAL, SHAONPIUS - Oak Ridge Institute For Science And Education (ORISE); Hladky, Laura; Fashing, Patricia; MCCREIGHT, JAMES - Retired ARS Employee; TURINI, THOMAS - University Of California; Wintermantel, William - Bill

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2021
Publication Date: 5/19/2021
Citation: Mondal, S., Jenkins Hladky, L.L., Fashing, P.L., McCreight, J.D., Turini, T.A., Wintermantel, W.M. 2021. First report of cucurbit yellow stunting disorder virus and cucurbit chlorotic yellows virus in melon in the Central Valley of California. Plant Disease. https://doi.org/10.1094/PDIS-01-21-0184-PDN.
DOI: https://doi.org/10.1094/PDIS-01-21-0184-PDN

Interpretive Summary: In the Central Valley of California, the leading melon (Cucumis melo) production region in the United States, sweet potato whitefly densities have increasingly reached levels causing damage to melons, resulting in increased potential for the emergence of whitefly-transmitted viruses. In California, the whitefly-transmitted yellowing viruses, cucurbit yellow stunting disorder virus (CYSDV) and cucurbit chlorotic yellows virus (CCYV) have been limited to the Sonoran Desert production regions of Imperial and Riverside counties since their emergence in 2006 and 2014, respectively where losses to these viruses have nearly eliminated fall melon production. CYSDV and CCYV have never been identified in the Central Valley, but the aphid-transmitted cucurbit aphid-borne yellows virus frequently infects Central Valley melon plants and produces symptoms identical to those of CYSDV and CCYV. Melon leaves showing symptoms typical of those caused by yellowing viruses, were collected from 106 melon plants in four commercial fields and a research plot in Fresno County, California, in October 2020. Molecular tests specific for detection of CYSDV, CCYV, CABYV, and cucurbit leaf crumple virus (CuLCrV) demonstrated that CABYV was by far the most prevalent virus, infecting 34/106 plants tested among the five fields. Seven plants from three fields were found to be infected with CYSDV. Only one plant was found to be infected with CCYV, and CuLCrV was not detected in any of the plants sampled. Each CYSDV and CCYV infection was confirmed using an additional detection method. This is the first report of CYSDV and CCYV in the Central Valley of California. In this survey, CABYV remained the predominant yellowing virus infecting melons in the Central Valley, but with 32 percent of plants infected by CYSDV, and the detection of CCYV, it will be necessary to monitor melons, other cucurbit crops and known alternate hosts of these viruses to determine the threat to melons in California’s Central Valley.

Technical Abstract: In the Central Valley of California, the leading melon (Cucumis melo) production region in the United States, whitefly (Bemisia tabaci Genn. MEAM1) densities have increasingly reached levels causing damage to melons, resulting in increased potential for the emergence of whitefly-transmitted viruses. In California, the whitefly-transmitted yellowing viruses, cucurbit yellow stunting disorder virus (CYSDV) and cucurbit chlorotic yellows virus (CCYV), both genus Crinivirus, fam. Closteroviridae, have been limited to the Sonoran Desert production regions of Imperial and Riverside counties since their emergence in 2006 and 2014, respectively where losses to these viruses have nearly eliminated fall melon production. CYSDV and CCYV have never been identified in the Central Valley, but the aphid-transmitted cucurbit aphid-borne yellows virus (CABYV; genus Polerovirus, fam. Luteoviridae) frequently infects Central Valley melon plants and produces symptoms identical to those of CYSDV and CCYV. Melon leaves exhibiting foliar mottling and interveinal chlorosis, symptoms typical of those caused by yellowing viruses, were collected from 106 melon plants in four commercial fields and a research plot in Fresno County, California, in October 2020. Total RNA and DNA were extracted separately from the same leaf from each plant to determine the presence of both RNA and DNA viruses. RT-PCR was used to amplify portions of the RNA dependent RNA polymerase (RdRp) gene of CABYV, CCYV and CYSDV. Total DNA was extracted and used in PCR to test for the presence of the whitefly-transmitted begomovirus, cucurbit leaf crumple virus (CuLCrV). Results demonstrated that CABYV was by far the most prevalent virus, infecting 34/106 plants tested among the five fields. Seven plants from three fields were found to be infected with CYSDV, and three of these from two fields were co-infected with CABYV. Only one plant was found to be infected with CCYV as a single virus infection, and CuLCrV was not detected in any of the plants sampled. Each CYSDV and CCYV infection was confirmed using a second set of primers that amplified sections of the coat protein gene of each virus. This is the first report of CYSDV and CCYV in the Central Valley of California. In this survey, CABYV remained the predominant yellowing virus infecting melons in the Central Valley, but with 32 percent of plants tested infected by CYSDV, and the detection of CCYV, it will be necessary to monitor both cucurbit crops and known alternate hosts for infection by these economically important viruses.