海南省稻瘟病菌对戊唑醇的敏感性及抗性菌株适合度

Susceptibility to Tebuconazole and Suitability of Resistant Strains ofMagnaporthe oryzae in Hainan Province

通过检测海南省稻瘟病菌对戊唑醇的敏感性及抗性菌株的适合度,了解海南省稻瘟病菌对戊唑醇的抗药性风险,为该杀菌剂的科学使用及抗性治理提供理论依据和策略。采用菌丝生长速率法测定2022年采集分离自海南省的144株稻瘟病菌株对戊唑醇的敏感性,根据菌株的敏感性频率分布,建立海南省稻瘟病菌对戊唑醇的敏感基线。选取敏感基线建立过程中测得的有效抑制中浓度(EC_(50))较低的敏感菌株15个,在连续选择压下进行抗药性驯化,对驯化出的菌株进行抗性水平划分,并测定抗性菌株的遗传稳定性及其对戊唑醇与杀菌剂吡唑醚菌酯、氟环唑、咪鲜胺、苯醚甲环唑、烯唑醇之间的交互抗性以及适合度。结果表明,供试144株菌株的EC_(50)值在0.176 9~0.998 0μg/mL,其中最不敏感菌株的EC_(50)值是最敏感菌株的5.64倍,EC_(50)平均值为(0.476 3±0.174 5)μg/mL。菌株的敏感性频率呈连续性单峰曲线分布,海南省稻瘟病菌对戊唑醇的敏感基线为0.476 3μg/mL。通过对15株敏感菌株进行药剂驯化共获得2株抗性菌株,其EC_(50)值分别为1.289 5μg/mL和1.868 4μg/mL,抗性倍数分别为5.38倍和6.65倍,均属低抗性水平。将上述2株抗性菌连续转接8代后,其始终保持低水平抗性。通过测定吡唑醚菌酯、氟环唑、咪鲜胺、苯醚甲环唑、烯唑醇对戊唑醇抗性菌株及亲本菌株的EC_(50)值并进行对比,结果显示,戊唑醇在对海南省稻瘟病菌的防治上与上述药剂均不存在交互抗性。对戊唑醇抗性菌株的离体适合度进行测定发现,相比于亲本菌株,2株抗性菌株的菌丝生长速率显著降低,且孢子产量均出现不同程度下降。此外,其对强酸和强碱环境更加敏感,致病力也大大减弱。因此,海南省稻瘟菌株对戊唑醇产生抗药性突变的频率较低,其抗性菌株的环境适合度显著下降,抗药性风险较低。此外,海南省稻瘟病菌对戊唑醇与常用杀菌剂无交互抗药性,可在生产上通过交互轮换使用或与多作用位点保护剂混合使用等策略来延缓抗药性的产生。

By detecting the susceptibility of Magnaporthe oryzae to tebuconazole in Hainan Province and studying the fitness of resistance strains,the resistance risk of M.oryzae to tebuconazole was understood,which would provide theoretical reference for the scientific use of fungicides and resistance management.The mycelial growth rate method was used to determine the susceptibility to tebuconazole of 144 strains of M.oryzae collected and isolated from Hainan Province in 2022,and the susceptibility baseline of M.oryzae in Hainan Province to tebuconazole was established based on the susceptibility frequency distribution of the strains.Fifteen susceptible strains with low effective inhibitory mid⁃concentration(EC_(50))measured during the establishment of the susceptibility baseline were selected for resistance domestication under continuous selection pressure,and the domesticated strains were classified into resistance levels,and the genetic stability and suitability of the resistant strains as well as the cross⁃resistance to the fungicides pyraclostrobin,flucycloxazole,imidacloprid,fenpyroximate,and aliconazole were determined.The EC_(50) values of the 144 strains tested ranged from 0.1769 to 0.9980μg/mL.The EC_(50) value of the least sensitive strain was 5.64 times that of the most sensitive strain.The average EC_(50) value was(0.4763±0.1745)μg/mL.The susceptibility frequencies of the strains were distributed in a continuous single⁃peak curve,and the susceptibility baseline to tebuconazole of M.oryzae in Hainan Province was 0.4763μg/mL.Through indoor domestication of 15 sensitive strains,a total of two resistant strains were obtained.EC_(50) values were 1.2895μg/mL and 1.8684μg/mL respectively,and resistance folds were 5.38 times and 6.65 times respectively,both of which were low resistance level.And after eight consecutive generations of transfer,the two resistant strains always maintained low⁃level resistance.The EC_(50) values of pyraclostrobin,epoxiconazole,prochloraz,difenoconazole,and diniconazole were measured and compared between the strains resistant to tebuconazole and their parental strains.The results showed that there was no cross⁃resistance in M.oryzae in Hainan Province between tebuconazole and the above chemicals.Through the in vitro fitness test of the tebuconazole⁃resistant strains,it was found that compared with the parental strains,the mycelial growth rate of the two resistant strains was significantly reduced,and the conidia production was reduced to varying degrees.In addition,they were more sensitive to strong acid and alkali environment,and their pathogenicity was greatly reduced.Therefore,the frequency of resistance mutations to tebuconazole in rice blast strains in Hainan Province is low,and the environmental suitability of their resistant strains is significantly reduced,resulting in a low risk of resistance.In addition,there is no cross⁃resistance between tebuconazole and commonly used fungicides in Hainan Province,and the development of resistance can be delayed by strategies such as cross⁃rotation or mixing with multi⁃site⁃of⁃action protectants in production.