Baseline Sensitivity to Mandipropamid Among Isolates of Phytophthora capsici Causing Phytophthora Blight on Pepper

Sensitivity to the new carboxylic acid amide fungicide, mandipropamid, of Phytophthora capsici causing pepper Phytophthora blight was determined on 187 isolates collected in Korea over 3 years, from 2005 to 2007. All isolates were sensitive to mandipropamid, with EC50 values for growth of mycelia ranging from 0.001 to 0.037 mu g/ml. Among the isolates, 147 (79.0%) isolates were sensitive to metalaxyl, whereas others were resistant to this fungicide. Mandipropamid had the same effect on mycelium growth of both metalaxyl-sensitive and metalaxyl-resistant isolates, indicating an absence of cross-resistance between these two fungicides. Comparison of the sensitivities of P capsici isolates showed a positive correlation between sensitivity to mandipropamid and dimethomorph (r(2)=0.8533). The results of this study indicate that there is no evidence for development of resistance to mandipropamid in this population of P capsici isolates collected in Korea.