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ARS Home » Southeast Area » Charleston, South Carolina » Vegetable Research » Research » Publications at this Location » Publication #359163

Research Project: Biology, Etiology and Host Resistance in Vegetable Crops to Diseases and Nematodes

Location: Vegetable Research

Title: Relative susceptibility of commercial watermelon varieties to powdery mildew

item Kousik, Chandrasekar - Shaker
item Ikerd, Jennifer
item MANDAL, MIHIR - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2019
Publication Date: 8/3/2019
Citation: Kousik, C.S., Ikerd, J.L., Mandal, M. 2019. Relative susceptibility of commercial watermelon varieties to powdery mildew. Crop Protection.

Interpretive Summary: Watermelon is an important vegetable crop grown in 44 states in the U.S.A. Many diseases and pests attack watermelon seedlings and plants and reduce their yield resulting in monetary loss for growers. One such disease, known as powdery mildew can infest watermelon seedlings and can cause reduced vigor or death of seedlings. Growers routinely spray pesticides to manage powdery mildew of watermelon. ARS scientists in Charleston, South Carolina evaluated many available varieties for their reaction to powdery mildew and identified that a few pollenizers and one variety has some level of resistance. The results indicate a need to develop newer varieties with resistance to powdery mildew as varieties with resistance to powdery mildew will help reduce the amount of pesticides applied on watermelon. The results of this study will be useful to watermelon growers, extension workers, seed industry and University researchers to help manage powdery mildew in the greenhouse where watermelon seedlings are generally grown.

Technical Abstract: Powdery mildew (PM) of watermelon caused by Podosphaera xanthii has been occurring frequently in recent years and growers routinely apply fungicides to manage PM. Powdery mildew is also known to cause a significant yield reduction in watermelon. The current study was conducted in 2014, 2015 and 2016 to determine the relative susceptibility of twenty six watermelon varieties (seeded and seedless) and three pollenizers to P. xanthii populations prevailing in Charleston, South Carolina. USVL677-PMS, which is highly susceptible to PM and USVL531-MDR, which is resistant to PM were included as controls. A randomized complete block design with three replications was used each year and plants were rated on a 0-10 scale of increasing disease severity. During all three years, USVL677-PMS was the most susceptible line with the highest area under disease progress curves (AUDPC). Disease severity durning last ratings on USVL677-PMS ranged from 61-82%. In comparison USVL531-MDR was very resistant to PM based on disease severity (1-3%) and AUDPC. The commercial pollenizers, SP5, SP6 and Lion were all resistant to PM (1-5% disease severity) and had significantly lower AUDPC compared to USVL677-PMS and most varieties. Among the red fleshed varieties, Suprema, (seedless variety) was relatively resistant compared to other seeded and seedless varieties. Most of the seeded varieties evaluated (e.g. Malali, Black Mama, Mickey Lee) were highly susceptible to PM, however, some were relatively less susceptible (e.g. Declaration) under field conditions. Currently very few to no varieties with high levels of resistance to PM are available and there is a need to develop newer resistant varieties as PM is occurring more frequently during the growing season.