Screening and identification of antagonistic bacteria against clubroot of Brassica rapa var.glabra Regel in Yunnan province
[Objective]The microbial strains with effective antagonistic effect against Yunnan cabbage clubroot were obtained through screen-ing,which provided potential strain resources for the biological control of Yunnan cabbage clubroot.[Method]Chinese cabbage plants with normal growth or mild disease and their rhizosphere soil were selected from the plot of the greenhouse in Sanbao town,Qilin district,Qujing city,Yunnan province.The strains with good bacteriostatic effect were isolated and screened,and their morphological characteristics,physi-ological and biochemical detection and molecular sequence analysis were performed.[Result]A total of 46 bacterial isolates were obtained through preliminary screening.Thirty bacterial strains were isolated from soil samples,of which TB-7 had the best inhibitory effect,and the inhibition rate of dormant spore germination was 76.88％;Sixteen strains of endophytic bacteria were isolated from Chinese cabbage,of which EB-15 had the best inhibitory effect and the germination inhibition rate of dormant spores was 67.38％.Through comparative analy-sis,strain TB-7 with the best antibacterial effect was selected as the target strain,and identified as a gram-positive Bacillus,with small colo-nies,pale yellow color,smooth and flat surface,and moist cells,opaque,with regular edges.The results of physiological and biochemical indexes showed that TB-7 was aerobic,and the test indicators of V-P,starch hydrolysis and growth at pH 5.7 were positive,citrate,propio-nate,d-xylose,L-arabinose,D-mannitol,gelatin liquefaction,7％NaCl growth and nitrate reduction were negative;The amplified product of 16S rDNA was about 1500 bp.The sequencing results showed that the homology between TB-7 strain and Cytobacillus firmus of the genus Bacillus reached 100％.[Conclusion]Through preliminary screening and identification,an antagonistic strain was screened with an inhibi-tion rate of 76.88％to dormant spores of Chinese cabbage clubroot,which would lay a foundation for the biological control of the increasingly serious local cabbage clubroot in Yunnan province.
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