Location: Crop Improvement and Protection Research
Project Number: 2038-22000-018-009-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Nov 1, 2019
End Date: Jun 30, 2022
Cucurbit yellow stunting disorder virus (CYSDV) has been impacting production of California melon and watermelon in the Imperial Valley and other desert production regions since 2006, and eliminated fall cucurbit production due to whitefly and virus pressure. Recently, CYSDV-resistant melon varieties have become commercially available, and there are efforts to return to summer and fall melon production in the region with these varieties. However, in 2014, Squash vein yellowing virus (SqVYV) emerged, which can cause collapse of watermelon vines, and in 2018, Cucurbit chlorotic yellows virus (CCYV) was identified, which looks identical to CYSDV but is not controlled by CYSDV resistance. We will enhance management and by determining reservoir hosts of CCYV and SqVYV in California, develop a universal detection system to rapidly differentiate all three viruses, which will improve resistance breeding efficiency, and develop recommendations to reduce virus transmission to cucurbits.
Molecular primers and probes will be developed (ARS PI) as a single reaction test for standard molecular detection (RT-PCR) for presence absence, and quantitative detection (RT-qPCR) of all three whitefly-transmitted viruses affecting California cucurbit production (CCYV, CYSDV, SqVYV) as well as Cucurbit aphid-borne yellows virus which cannot be distinguished visibly from the others. Standard detection will determine presence or absence of each virus, whereas quantitative detection will provide levels of each virus in a single reaction. Validation will be performed on known samples from both UC Davis and USDA labs and new field collections. New methods will be used to evaluate presence and titer of target viruses in weed and crop plants collected from field locations in Imperial County and nearby regions (UC Davis/USDA), as well as to scout for the emergence of these viruses during the fall whitefly outbreaks in the Central Valley. A minimum of 12 melon or watermelon fields sampled in desert each late spring melon season, and as many as available during the fall season. Weed samples will be collected from near melon/watermelon fields in spring and fall, as well as sampling of nearby crops to determine incidence and titer of each virus in regional plants (UC Davis/USDA). High titer hosts of CCYV and SqVYV identified in year 1 will be used to evaluate efficiency of transmission from these hosts to melon and watermelon) (USDA/UC Davis). Primers developed in Year 1 will be used to evaluate germplasm for incidence and titer of target viruses in field trials for resistance (USDA) to whitefly-transmitted viruses in Imperial Valley in both years (USDA). Results will be reported through meetings and publications, with relevant summary information added to the UC IPM website as described below.