Researcher(s)
- Morgan Oliver, Plant Science, University of Delaware
- Shiv Singla, Plant Science, University of Delaware
Faculty Mentor(s)
- Alyssa Betts, Plant and Soil Science, University of Delaware
Abstract
Phytophthora capsici is a devastating pathogen of cucurbits that causes significant yield losses. Watermelon is one of DE’s most valuable cucurbits, ranking 8th nationally. Additionally, pumpkins are another important crop grown on 17% of DE’s vegetable farms. The fungicide active ingredient mefenoxam is widely used to manage diseases caused by oomycetes, but increased resistance to mefenoxam has been reported among P. capsici isolates. Mefenoxam sensitivity screening conducted in 2014-2015 showed that 6% of the isolates were insensitive and 28% isolates had intermediate sensitivity to mefenoxam. To update sensitivity profiles, 18 isolates of P. capsici collected from pumpkin fields in 2023 were screened using mefenoxam amended media at concentrations 0, 0.01, 0.1, 1, 10, and 100 ug/ul. Measurement of mycelial growth at these concentrations was used to determine the effective concentration to inhibit mycelial growth by 50% (EC50). In initial screening, 28% of isolates (n=5) were not inhibited by 100 ug/ul concentrations. Isolates with reduced sensitivity will be selected as candidates for molecular analysis to confirm resistance. In addition to fungicide sensitivity screening, isolates were screened for A1 and A2 mating type and it was determined that both mating types are present, suggesting persistence of these isolates through overwintering oospores. Knowledge of the current sensitivity profiles of P. capsici will help to improve disease management recommendations as mefenoxam sensitivity shifts in P. capsici populations.