ARS | Publication request: Baseline Sensitivity of Phytophthora Capsici Isolates from the Southeast US to Mandipropamid

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 2, 2009
Publication Date: July 26, 2009
Citation: Kousik, C.S., Donahoo, R.S., Keinath, A.P. 2009. Baseline Sensitivity of Phytophthora Capsici Isolates from the Southeast US to Mandipropamid. Phytopathology. 99:S67.

Technical Abstract: The plant pathogen Phytophthora capsici is rapidly becoming an important limiting factor in vegetable production in the southeastern United States. In 2008, a new fungicide, mandipropamid (trade name: Revus) was labeled for managing P. capsici on vegetable crops. In this study, we used a collection of 28 P. capsici isolates from the southeastern United States to determine baseline sensitivity values to this new fungicide. Of these 28 isolates, 5 were from NC, 8 from SC, 9 from GA, and 6 from FL. All isolates were confirmed as P. capsici based on morphology and by using P. capsici-specific PCR primers. An in vitro biological growth assay using V8-juice agar amended with four concentrations of mandipropamid (0, 0.0015, 0.015, 0.15 mg/L) was used to determine EC50 values. The EC50 values for mycelial growth on amended media ranged from 0.0125 mg/L to 0.0292 mg/L (mean= 0.0219 mg/L). Mycelial growth of all isolates was completely inhibited at 0.15 ppm. EC50 values for production of sporangia ranged from <0.0015 mg/L to 0.032 mg/L. EC50 values for zoospore germination ranged from <0.0015 mg/L to 0.0105 mg/L. These baseline values will be useful in monitoring changes in sensitivity of P. capsici populations as mandipropamid is used across the southeastern United States in vegetable production.