Sensitivity And Resistance Risk Assessment Of Clarireedia Spp.to Three Fungicides In Beijing And Tianjin

Dollar spot is one of the most common turf diseases,which seriously damages the ornamental and use value of lawns.At present,chemical control is still the main way to control the dollar spot.Since the mainstream fungicides in the market have been used for decades,some research on the decrease of sensitivity of Clarireedia to fungicides have been reported in recent years.However,there are no research data on the resistance of Clarireedia to boscalid,iprodione and fludioxonil in Beijing and Tianjin.Therefore,this article established a sensitivity baseline and carried out a resistance risk assessment by measuring the susceptibility of 154 strains of dollar spot pathogen in Beijing and Tianjin to three different types of boscalid,iprodione and fludioxonil..The results of the study are as follows:The frequency distribution of sensitivity of 154 strains in this experiment to three different fungicides is a continuous single peak curve,and the verified curve obeys the normal distribution.The average EC₅₀ measured in this study can be used as the sensitivity baseline of the three fungicides in Beijing and Tianjin.The baseline sensitivity to boscalid,iprodione and fludioxonil were（4.5837±0.8249）μg/m L,（0.3608±0.0426）μg/m L and（0.0011±0.0006）μg/m L.154strains have different degrees of resistance to boscalid,and the resistance levels of different golf courses are different.There was no obvious correlation between the sensitivity of the pathogen to boscalid and iprodione,boscalid and fludioxonil.The 154 strains of dollar spot pathogens were classified into three resistance phenotypes:high resistance（HR）,low resistance（LR）and sensitive（SS）.strains based on their resistance to boscalid in this study,two strains from the above resistance phenotypes,respectively,were selected and the hyphae growth,biomass,oxalic acid production of these pathogens were measured,along with the disease incidence,disease index and malondialdehyde（MDA）content in creeping bentgrass leaves were determined after creeping bentgrass were inoculated by the 6 strains to evaluate the pathogenicity of pathogens with different sensitivities to boscalid.The results showed that the pathogenicity of dollar spot pathogen strains with different sensitivity to boscalid was significantly different.Compared to the LR and SS strains,the HR strains performed lower hyphae growth rate（decreased by 25.2%）,biomass and oxalic acid production as well as the lower diseases incidence（decreased by more than 32.4%,27.3%）,diseases index decreased by 49.5%～84.1%.MDA decreased by more than 38.4%.On the whole,the pathogenicity of strains with high resistance to boscalid was the weakest,the pathogenicity of strains that sensitive to boscalid was the strongest,and that of LRs was between the two.The results serve a useful reference for appropriate application of fungicides and effective control of dollar spot.