In recent years,the'black stalk disease',a new symptom of radish,had become increasingly serious in Tianjin.The purpose of this study was to accurately identify the pathogen,and carry out fungicide toxicity test in lab for screening of high efficiency,low toxicity fungicide in the light of target pathogens.In this study,the occurrence of radish'black stalk'in the field in Tianjin was investigated.The pathogen was identified by morphological,pathogenicity and molecular biology.Nineteen kinds of fungicides commonly used for bacterial control were selected for screening by the inhibition comparison and toxicity testing.The results showed that the pathogenic bacteria causing the'black stem disease'of local Weiqing radish were Xanthomonas campestris pv.campestris(Pam.)Dawson,which was a new symptom of radish black rot disease.The isolated pathogenic strains exhibited pathogenicity differentiation,among which the highly pathogenic strain LB-B was selected.The results of laboratory toxicity test showed that there were 10 kinds of fungicides with different effects of inhibition on radish black rot.Among them,0.3%tetramycin AS and 10%propylthiazole SC had the best inhibition effect on radish black rot,and their inhibition rates were above 89.52%at 1 000 mg·L-1 concentration.The EC50 of 0.3%tetramycin AS and 10%propylthiazole SC were 156.69 mg·L-1 and 174.04 mg·L-1,respectively,which showed the stable and the long duration of efficacy in the field.The above experimental results provided candidate fungicide for effective control of radish black rot disease.
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