Sensitivity of Fusarium asiaticum to a novel succinate dehydrogenase inhibitor fungicide pydiflumetofen

Fusarium head blight (FHB) or scab mainly caused by Fusarium asiaticum is a devastating fungal disease in wheat. In China, carbendazim (MBC) and its co-formulated mixture with other fungicides are the main fungicides for controlling the disease. But resistant populations have developed severely in the field. The fungicides for controlling the disease are limited. So screening novel fungicides for controlling FHB is urgent. The fungicide pydiflumetofen (development code number: SYN545974),3-(Difluoromethyl)N-methyl-N-[1-methyl-2-(2,4,6-trichlorophenyl)ethyl]-1H-pyrazole-4-carboxami.d.e, is a novel succinate dehydrogenase inhibitor (SDHI) that was developed by Syngenta. In this study, the baseline sensitivities for different isolates of F. asiaticum from various regions of China to pydiflumetofen were established. The 50% effective concentration (EC50) value of pydiflumetofen on suppressing mycelial growth against 116 isolates of F. asiaticum was 0.019-0.2084 μg/ml and their average value was 0.0745 ± 0.0367 μg/ml. The EC50 value of pydiflumetofen on suppressing conidium germination was 0.0583-0.4237 μg/ml and their average value was 0.1813 ± 0.0861 μg/ml. The results indicated that the fungicide had strong inhibition effect on mycelial growth and conidium germination against F. asiaticum in vitro. The EC50 values distribution of 116 isolates measured by mycelial growth assay or by conidium germination assay was a unimodal curve and could be used for detecting any sensitivity changes of F. asiaticum populations to pydiflumetofen in the future. The results of cross-resistance analysis indicated that there was no positive or negative cross-resistance between pydiflumetofen and carbendazim/phenamacril. In field trials, though FHB was very severe, pydiflumetofen at 125, 150 and 200 g ai ha−1 all provided more than 80% control efficacy which was significantly higher than that of phenamacril at 375 g ai ha−1 or MBC at 600 g ai ha−1 in 2015 and 2016. In conclusion, pydiflumetofen had very high activity against F. asiaticum in vitro and excellent efficacy for controlling FHB could also manage carbendazim-resistant F. asiaticum populations in the field.