Sensitivity of Venturia carpophila from China to five fungicides and characterization of carbendazim resistant isolates.

Peach scab is a fungal disease caused by Venturia carpophila, which can significantly reduce peach yield and quality. Fungicide application is the main control measure for peach scab worldwide. For better understanding of the fungicide resistance status and making suitable management strategies, the sensitivity of 135 single-spore V. carpophila isolates to commonly used fungicides carbendazim, iprodione, propiconazole, azoxystrobin and boscalid were determined using microtiter plate test method. Results showed that the mean EC50 values of tested isolates to iprodione, propiconazole, azoxystrobin and boscalid were 16.287 µg/ml, 0.165 µg/ml, 0.570 µg/ml and 0.136 µg/ml, respectively. The EC50 values of V. carpophila isolates to four fungicides displayed unimodal frequency distributions, indicating no resistance occurred to these fungicides. On the other hand, bimodal frequency distribution was observed for carbendazim, indicating that the V. carpophila developed resistance to carbendazim. Actually, the resistance was widely detected from all of the 14 provinces. Molecular analysis showed that the point mutation E198K of the TUB2 gene determined the high resistance, while the E198G conferred the moderate resistance. Both moderate and high resistances were stable, and the resistant isolates did not show significant fitness penalties. On the contrary, some resistant isolates showed better competitiveness under certain stresses. This is the first report to detect the sensitivity of V. carpophila to fungicides which enables future monitoring of fungicide resistance and provides the basic information for making suitable peach scab management strategies.