华南地区瓜类疫霉对甲霜灵的田间抗药性

Field resistance of Phytophthora melonis to metalaxyl in South China

摘要:

摘要: 【目的】了解华南地区瓜类疫霉( Phytophthora melonis) 对甲霜灵的田间抗药性。【方法】2007－2010年从广西、广东两省( 区) 9 个市冬瓜和黄瓜产区采集疫病样品，分离纯化瓜类疫霉，分别采用菌落生长速率法和叶盘漂浮法测定瓜类疫霉对甲霜灵的敏感性，并用药剂驯化方法从敏感性菌株诱导瓜类疫霉抗甲霜灵突变体。【结果】从9 个市24 个样点共分离纯化获得193 株瓜类疫霉，抗药性检测结果表明，敏感菌株、中等抗性菌株和抗性菌株分别占测试菌株的29. 0%、18. 1% 和52. 8%;

Abstract:

Abstract: ［Objective］Phytophthora melonis is the casual agent of wax gourd and cucumber Phytophthora blight which becomes a constraint for sustainable production of the related crops．Metalaxyl is one of the principal fungicides for controlling the disease now． The objectives of the present study were: (1) to investigate the baseline sensitivity and field resistance of P．melonis to metalaxyl in South China;(2) to test the occurrence of metalaxyl-resistant mutants from metalaxyl-sensitive wild type strains exposed to the fungicide; and (3) to monitor the development of metalaxyl resistance in P． melonis population．［Methods］ Over 400 samples of wax gourd and cucumber Phytophthora blight were collected from Guangxi Zhuang Autonomous Region and Guangdong province during 2007-2010，and 193 strains of P．melonis were isolated and purified．The sensitivity of the isolated strains to metalaxyl was tested using mycelial growth rate method in vitro and floating-leaf-disk method in vivo，respectively． The metalaxyl-sensitive strains were induced on PDA plates containing 10 μg/mL metalaxyl．［Results］The sensitive，moderately resistant and resistant strains were recorded as 29.0%，18.1% and 52.8%，respectively，among 193 tested strains．The frequency and level of resistance of P．melonis from Guangdong were higher than that from Guangxi．The strains from cucumber was generally more resistant to metalaxyl than those from wax gourd． The metalaxyl-resistant strains were frequently detected as predominant populations in most of the sampling sites and the highest resistance index (4226.9) was confirmed．Metalaxyl-resistant (Mrt) mutants could be isolated from approximately 60% of the sensitive wild-type strains．The resistance level of the Mrt mutants was 189－407 times higher than that of their sensitive parental strains．The EC50 values of 9 sensitive strains from a sampling site without a record of phenylamide fungicide application ranged from 0.0429 to 0.5461 μg/mL．Their mean EC50 value (0.3200±0.1617μg/mL) was considered as the baseline sensitivity of P． melonis to metalaxyl in South China．［Conclusion］Metalaxyl-resistant strains universally occur in South China，especially in the vegetable-growing areas with a longer history of metalaxyl application． The establishment of the baseline sensitivity of P． melonis to metalaxyl will provide a sciencebased guide for evaluating and further monitoring resistance of the pathogen to the fungicide．