Snsitivity Of Valsa Mali To Difenoconazole In China

Apple Valsa Canker,commonly known as rot skin disease,caused by the fungus Valsa mali(anamorph: Cytospora sacculus),mainly in the adult fruit trees,is one of the major diseases of apple in China.The disease causes the decline in apple production,poor quality,and restricts the development of China’s apple industry.In order to confirm the sensitivity of Valsa mali to triazole fungicides difenoconazole,109 strains of Valsa mali were isolated from the representative location of Shaanxi,Henan,Shanxi,Shandong,Xinjiang and Liaoning province.The effective dose to reduce mycelial growth by 50%(EC50 values)of each strain to triazole fungicide difenoconazole was determined by five different concentrations of fungicides.The results demonstrated that the 50% effective concentration values(EC50 values)of the 109 strains to difenoconazole ranged from 0.003 to 0.123 μg/m L,and the mean EC50 values were 0.044 ± 0.029 μg/m L,and most of them are gathered between 0.003 to 0.09 μg/m L.The difference of the maximum value and the minimum value was 0.12 μg/m L,indicating that the range of EC50 values of Valsa mali was big to triazole fungicides difenoconazole,indicating that there was different sensitivity to the drug between individuals in the group.The frequency distribution of the EC50 value is a continuous unimodal curve,and P=0.135>0.05 by Kolmogorov-Smirnov Test,therefore,the average EC50 of 109 strains was 0.044 μg/m L,which could be used as the sensitive baseline of Apple Valsa Canker to difenoconazole.The result of Duncan test showed that there were significant differences of the sensitivities of 109 Valsa mali strains to triazole fungicide difenoconazole in different years,the sensitivity of Valsa mali strains to difenoconazole was weakened year by year.Indicating that the continuous use of chemical pesticides for many years will cause increased resistance to plant pathogens.Frequent use of triazole fungicides may increase the resistance of pathogens to triazole pesticides.Many pathogens have different resistance to different pesticides,so the frequent use of other types of chemical pesticides may also increase the pathogen resistance to triazole pesticides.The result of Duncan test showed that the sensitivities to difenoconazole of Valsa mali from different regions were no evident difference in the strains.This showed that the isolates from Liaoning were more sensitive to difenoconazole than the isolates from other provinces,the EC50 value of strain from Liaoning was the lowest.The sensitivities to triazole fungicide difenoconazole of Valsa mali strains in Shaanxi province were disparity in different years.There were significant differences in the sensitivity of apple tree rotting bacteria to difenoconazole in Shaanxi Province in 2009,2010 and 2011,there was no significant difference between 2010 and 2012.