First report of cucurbit yellow stunting disorder virus infecting cucurbit crops in Jamaica.

Abstract

The increasing prevalence of whitefly-transmitted viruses affecting cucurbit crops has emerged as a significant concern for global cucurbit production. Two of the most widely prevalent threats in the Americas are cucurbit yellow stunting disorder virus (CYSDV) and cucurbit chlorotic yellows virus (CCYV) (Crinivirus, Closteroviridae). These viruses induce similar foliar symptoms on cucurbit crops (Mondal et al., 2023) leading to loss of photosynthetic capability and decreased yields. Cantaloupe (Cucumis melo), watermelon (Citrullus lanatus), and cucumber (Cucumis sativus) are major cucurbit crops in St. Elizabeth, Jamaica, which is the principal fruit and vegetable producing region of the country. In August 2018, foliar symptoms were observed on cantaloupe, watermelon, and cucumber plants in several commercial farms in St. Elizabeth. These symptoms, mainly on the older leaves, consisted of severe yellowing or interveinal mottle and they appeared more pronounced on cantaloupe and cucumber plants compared to watermelon. Growers noticed the production of smaller than normal fruit. Disease incidence ranged from 10 to 100% and whiteflies (Bemisia tabaci Gennadius) were observed in the fields. To identify virus(es) associated with the disease, six plants (cantaloupe [n = 3], cucumber [n = 1] and watermelon [n = 2) exhibiting symptoms were sampled from four fields for preliminary screening. Total RNA was extracted from leaf tissues as described in Tamang et al. (2021) and samples tested by a multiplex reverse transcription RT-PCR method that targeted the RNA-dependent RNA polymerase (RdRp) of the whitefly transmitted viruses, CYSDV, CCYV, squash vein yellowing virus (SqVYV), and the aphid- transmitted cucurbit aphid-borne yellows virus (CABYV) (Mondal et al. 2023). RT-PCR amplified the expected 494-bp fragment of the CYSDV RdRp gene (Mondal et al., 2023) from two symptomatic plants; one cantaloupe, one cucumber, as well as from CYSDV-infected control plants but not from healthy controls. Further testing was conducted during the June-August 2020 growing season after similar symptoms were observed on additional farms in St. Elizabeth and two regions, Manchester and Clarendon, located to the east of St. Elizabeth. Twenty-one cucurbit leaf samples (11 cantaloupe, seven watermelon and two cucumber from St. Elizabeth and one cantaloupe from Clarendon) exhibiting foliar yellowing progressing from the crown outward, and mottling were collected. Whiteflies (5) from these fields in St. Elizabeth and 20 asymptomatic weed samples were also collected and sent to the USDA-ARS laboratory at Salinas, CA. Total RNA from leaf samples was extracted as described above and tested for CYSDV, CCYV, and CABYV. Total leaf DNA was also extracted (Mondal et al. 2016) and assayed with PCR (Gilbertson 2001) to detect the presence of the whitefly-transmitted cucurbit leaf crumple virus (CuLCrV), a begomovirus, commonly found in the southeastern United States (Gadhave et al., 2018; Keinath et al., 2018). Nineteen of the 21 cucurbit samples tested positive for the presence of CYSDV by RT-PCR (Mondal et al. 2023). Of the 19 CYSDV-positive samples, 13 cantaloupe, one cucumber, and five watermelon samples were singly infected with CYSDV, and one cantaloupe sample was infected with both CYSDV and CABYV. Amplicons of the Jamaica isolate from cantaloupe were sequenced (OR399555) and a 494 nt section of the RdRp gene was found to share 100% sequence identity to the Arizona 1 isolate (EF547827.1). The presence of CYSDV, was further confirmed using a second set of primers that amplified a 394-nt portion of the CYSDV coat protein gene (Polston et al., 2008). Among the weed samples, CABYV was detected in one sample from a Leonotis nepetifolia plant (Lamiaceae) and two Cleome sp. (Capparaceae) collected from St. Elizabeth. None of the crop and weed samples tested positive for CCYV or CuLCrV. DNA from whiteflies was extracted and assayed with PCR using species specific primers (Chen et al. 2016). All whiteflies were identified as B. tabaci cryptic species MEAM1, which is widely known an efficient vector of CYSDV (Berdiales, et al. 1999). This is the first report of CYSDV in Jamaica and its first known occurrence in these hosts within the country. Further monitoring of cucurbit crops and the whitefly vector is warranted to better understand the epidemiology.