Sensitivity of Sclerotinia sclerotiorum to fluopyram and its mixtures in Henan Province

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a devastating disease and can significantly reduce production in oilseed rape. To determine the sensitivity of S. sclerotiorum to fluopyram, 127 S. sclerotiorum isolates were collected from different oilseed rape fields from 5 cities in Henan Province in 2015 and 2016, and the median effective concentrations (EC₅₀ values) of fluopyram for S. sclerotiorum isolates were analyzed by the mycelial growth rate method. The result showed that the EC₅₀ values ranged from 0.0100 to 0.0989 μg/mL, and the mean EC₅₀ value was (0.0546 ± 0.0228) μg/mL (mean ± SD). The frequency distribution of the EC₅₀ values for 127 S. sclerotiorum isolates was a unimodal and continuous curve, which demonstrated that there was no resistant subpopulation among these isolates. Thus, the mean EC₅₀ value could be used as a baseline for monitoring fluopyram resistance in field isolates of S. sclerotiorum in Henan Province. The allied toxicity of fluopyram and prothioconazole, metconazole, carbendazim, fludioxonil or dimethachlone at volume ratios of 1 : 5, 1 : 3, 1 : 1, 3 : 1 and 5 : 1 to S. sclerotiorum were detected by the method of mycelial growth assay. The result showed that the mixtures of fungicides with the volume ratio of 1 : 5, 1 : 3, 1 : 1, 3 : 1, and 5 : 1 showed a synergy ratio ranging from 0.51 to 5.86, indicating an additive or synergistic inhibition effect. The mixture of fluopyram and fludioxonil with a volume ratio of 1 : 1 was demonstrated to have the strongest synergistic inhibition effect with the maximum synergy ratio. The results indicated that fluopyram be used in combination with prothioconazole, metconazole, carbendazim, fludioxonil, and dimethachlone, and these results could provide a basis in controlling the Sclerotinia stem rot caused by S. sclerotiorum.