Baseline sensitivity of Brazilian Mycosphaerella fijiensis isolates to protectant and systemic fungicides

Black Sigatoka caused by Mycosphaerella fijiensis is a foliar disease that affects banana plants and large amounts of fungicides are required to prevent crop losses. Intensive applications of single-site fungicides can select for fungicide-resistant isolates. The objective of this study was to assess the sensitivity of 60 isolates of M. fijiensis to commonly used fungicides. Using two different protocols, microtiter and Petri plate tests, the effective concentration at which mycelium growth is reduced by 50% (EC50) was determined for thiophanate-methyl, tebuconazole, chlorothalonil and mancozeb. Additionally, partial sequences of the cytochrome b gene were obtained for 46 isolates to detect the G143A mutation, commonly associated with strobilurin resistance. The EC50 values for tebuconazole and thiophanate- methyl ranged from 0.02 to 1.39 and from 0.008 to 8.22 mu g mL(-1), respectively. For chlorothalonil, the lowest and highest EC50 values were 0.39 mu g mL(-1)and 53.7 mu g mL(-1), respectively. For mancozeb, approximately 50% of the isolates had EC50 values greater than 1000 mu g mL(-1). No mutation was found in the isolates assayed for strobilurin resistance. There was no correlation between sensitivity levels to any fungicide and geographic region. Low EC50 values were estimated for most fungicides but, some isolates had high EC50 values for mancozeb.