Screening and identification of antagonistic strain DL-59 of Bacillus velezensis against Alternaria brassicae and biocontrol efficiency

The experiment used the Alternaria brassicae as test microorganism.By using an improved agar plate diffusion method,one strain with a rather stronger antagonistic activity,which can produce spore,was isolated form soil.Morphological,physiological and biochemical tests combined with 16S rDNA sequence analysis were carried out to identify the strain DL-59.Its control effect was studied in the basin culture and the plot trials.The result showed that 200 strains were isolated from soil.Through the preliminary screening 20 antagonistic bacteria strains were obtained.After the secondary screening,a strain named DL-59 with a rather stronger antagonistic activity was obtained.Its diameter of inhibition zone reached 23 mm.It was identified as Bacillus velezensis.The control efficacy is 79.07%,and the result of the plot trials showed that DL-59 has a visible preventive effect on cabbage black spot disease.Since the strain could produce spores,it is important for the storage time of the microbial agents.