黄瓜白粉病菌对甲基硫菌灵的敏感性及室内抗性突变体生物学性状
Sensitivity of Podosphaera xanthii to thiophanate-methyl and characteristics of resistant mutants

为明确山西省黄瓜白粉病菌对甲基硫菌灵的抗药性现状, 采用叶盘漂浮法测定了不同地区119株菌株对甲基硫菌灵的敏感性, 用紫外线照射和药剂驯化方式诱导获得了甲基硫菌灵抗性突变体, 并比较了亲本菌株与突变体的生物学性状。结果表明, 119株菌株的EC50在0.48～14.37 μg/mL之间, 平均EC50为2.89±2.69 μg/mL。不同地区菌株敏感性差异较大, 采自未使用过任何杀菌剂的忻州市菌株敏感性最高, 平均EC50为1.03±0.27 μg/mL, 可作为黄瓜白粉病菌对甲基硫菌灵的敏感基线;运城市菌株敏感性最低, 平均EC50为7.02±3.12 μg/mL, 其中菌株YC01的EC50是敏感基线的13.98倍。3株室内诱导突变体均为高抗, 突变体XZ11-2的抗性倍数达到94.96倍, 抗性突变频率为1.5×10-3。药剂处理条件下, 突变体的侵染频率、病情指数、产孢量和孢子萌发率均显著低于亲本敏感菌株;抗:感菌株分生孢子以80:20混合培养7代后, 抗性菌株频率变化不明显;以20:80混合培养7代后, 抗性频率降低甚至消失。表明黄瓜白粉病菌对甲基硫菌灵的抗性在选择压力低的情况下有可能丧失。
To assess the resistance risk of Podosphaera xanthii to thiophanate-methyl, the sensitivity of 119 isolates collected from Shanxi Province was detected by using leaf disk floating method; thiophanate-methyl resistant mutants were obtained by UV irradiation and chemical screening in the laboratory, and the fitness parameters and competition ability of resistant and sensitive isolates were measured. The results showed that the EC50 values of isolates from different regions varied from 0.48 to 14.37 μg/mL with a mean of 2.89±2.69 μg/mL. The mean EC50 value of 60 isolates collected from Xinzhou, where fungicide had not been used before, was 1.03±0.27 μg/mL, which could be regarded as the baseline sensitivity of P. xanthii to thiophanate-methyl. The sensitivity of isolates from Yuncheng was the lowest, with a mean EC50 value of 7.02±3.12 μg/mL, but the resistance ratio of YC01 was 13.98 times the baseline sensitivity. The resistance level of three thiophanate-methyl resistant mutants was high, and the resistance ratio of XZ11-2 was 94.96 times. The fitness of resistant mutants was significantly lower than sensitive isolates. The ratio of resistant and sensitive conidia had not significantly changed when they were cultured at the proportion of 80:20 for seven generations; however, the frequency of resistant isolates decreased when mixed with 20:80. The results indicated that the resistance of Podosphaera xanthii to thiophanate-methyl could gradually decline when the selection pressure became lower.