Bioactivity of Y13149 and its sensitivity baseline of Rhizoctonia solani

The bioactivity of Y13149, N-(2-(2,4-dichlorophenoxy) phenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, a novel succinate dehydrogenase inhibitor discovered through pharmacophore-linked fragment virtual screening by Huazhong Normal University, was evaluated by the method of mycelial growth rate. Results indicated that it exhibited good inhibitory activities against 10 tested plant-pathogenic fungi with the EC50 of 0.008-15.25 mg/L and the highest inhibition rate was observed in the case of Rhizoctonia solani. However, Y13149 had lower activities against Phytophthora capsici and Pythium catenulatum. In field experiments, the control efficacy of Y13149 for the rice sheath blight disease is, on average, 79.6% at the dose of 75 g/hm2, which is comparable with that of trifuzamide (77.3% at the dose of 75 g/hm2). Further study suggested that the EC50 for the tested population (n=125) of R.solani collected from Zhejiang and Jiangsu Province fitted unimodal distribution and varied from 0.002 to 0.259 mg/L with the mean of (0.021 ±0.008) mg/L, which could be adopted as the baseline sensitivity of R.solani to Y13149 to monitor the sensitivity shift.