Sensitivity baseline of Alternaria solani to pyrisoxazole and the mode of action of pyrisoxazole

To study the sensitivity of Alternaria solani to pyrisoxazole, 166 single-spore isolates were collected from tomato fruits or leaves infected by A. solani without exposure to pyrisoxazole in open field or greenhouse in Shanxi province, Inner Mongolia Autonomous Region, Shandong province, Hainan province, Jiangsu province, Fujian province and Shaanxi province. The sensitivity of each isolate to pyrisoxazole was determined by mycelial growth inhibition rate. The range of EC50 values were from 0.11 mg/L to 2.29 mg/L, and the sensitivity frequency was normally distributed. Thus, the sensitivity baseline was established with the mean EC50 value (0.56 ±0.39) mg/L of pyrisoxazole. There were significant differences in the mean EC50 value of each collected district. The isolates from Fujian province were the most sensitive, while the isolates from Shanxi province (Datong, Jinzhong and Changzhi) were the least sensitive to pyrisoxazole. Pyrisoxazole provided excellent protective and curative activity on A. solani when applied at 200 mg/L, and it showed the best control efficacy before the artificial inoculation in 4 days and after inoculation in 2 days. Consequently, there is a good application prospect to pyrisoxazole for controlling tomato early blight.