Susceptibility to Tebuconazole and Suitability of Resistant Strains of Magnaporthe oryzae in Hainan Province
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(EC50)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 EC50 values of the 144 strains tested ranged from 0.176 9 to 0.998 0 μg/mL.The EC50 value of the least sensitive strain was 5.64 times that of the most sensitive strain.The average EC50 value was(0.476 3±0.174 5)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 0.476 3 μg/mL.Through indoor domestication of 15 sensitive strains,a total of two resistant strains were obtained.EC50 values were 1.289 5 μg/mL and 1.868 4 μg/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 EC50 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.
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