Sensitivity of potato Phytophthora infestans to novel fungicide cyazofamid in China and its inhibitory effect against pathogen
[Objective]The study aimed to monitor the resistance level of Phytophthora infestans populations on potato towards novel efficient fungicide cyazofamid,as well as to investigate its anti-oomycete effect so as to provide scientific reference for the green control of late blight and promote rational utilization of the fungicide.[Method]The sensitivity of P.infestans isolates collected from four dominant potato regions in China during 2015 to 2020 was determined by fungicide-amended plate method,and the EC50,resistance multiple and resistance index were calculated to assess the resistance level of P.infestans to cyazofamid in China.The inhibitory phenotypes of cyazofamid on different growth and development stages of P.infestans and its effect on pathogenicity were determined in vitro.[Result]The frequency distribution of sensitivity of 160 isolates of P.infestans from 4 dominant regions of China showed a continuous single peak curve,which was normal distribu-tion.The EC50 values ranged from 0.0666 to 3.8498 μg/mL,with an average EC50 value of(0.5286±0.5394)μg/mL.The results indi-cated that P.infestans isolates were more sensitive to cyazofamid,with a proportion of 89.0％.This suggested that the sensitive isolates of P.infestans were the predominant population.In addition,low-resistance isolates were detected,and moderate or high-resistant isolates were not detected.The resistance level showed that there was no significant difference in the average EC50 value and the average resistance multi-ple of P.infestans to cyazolium among the four dominant potato regions.The resistance frequency was more than 10％between northern sin-gle-planting region and southwestern mixed planting region.The results showed that cyazofamid significantly inhibited the life stages of P.in-festans such as mycelial growth,sporangium formation,direct sporangium germination,zoospore release and cyst germination.This inhibition seriously compromised the pathogenicity of P.infestans.[Conclusion]Chinese P.infestans isolates exhibite greater sensitivity to cyazofamid.The resistance index of P.infestans in the four dominant regions is found to be similar and extremely low,indicating a low resistance risk.Cyazofamid inhibites the growth and development of P.infestans,thereby affecting its pathogenicity.
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