Baseline sensitivity and control efficacy of fluazinam against Sclerotinia sclerotiorum

Abstract

Sclerotinia sclerotiorum is a filamentous fungal phytopathogen capable of infecting many economically important crops and vegetables. The dinitroaniline fungicide fluazinam had not been registered for control of S. sclerotiorum in China until April 2014. In this study, control efficacy of fluazinam was determined and baseline sensitivity of S. sclerotiorum to this fungicide was established based on EC50 values of 150 isolates sampled from different regions of China in 2013. Results showed that the frequency distribution of fluazinam EC50 values was a unimodal curve with a mean EC50 value of 0.0019 ± 0.0013 (SD) μg/ml and a range of individual EC50 values from 0.0004 to 0.0056 μg/ml. Applied as a preventive fungicide in pot experiments, fluazinam at 2, 8 and 32 μg/ml provided control efficacies of 39, 88 and 100 %, respectively, which were much higher than those of dimethachlon. Curative control efficacy of fluazinam was significantly lower than its preventive control efficacy. There was no positive cross-resistance between fluazinam and carbendazim or dimethachlon. These results indicate that fluazinam is highly effective and should be used as a preventive rather than curative fungicide for control of S. sclerotiorum. In addition, no significant correlation (P = 0.245) was found between EC50 values for fluazinam and those for pyraclostrobin. No significant correlation (P = 0.350) between fluazinam EC50 values and levels of virulence to oilseed rape plants was detected, either, whereas there was a significantly negative correlation (P = 0.009, r = −0.562) between fluazinam EC50 values and mycelial growth on PDA media.