Screening And Identification Of Antagonistic Bacteria Against Xanthomonas Oryzae And Antagonistic Mechanism Research

Bacterial leaf streak(BLS),caused by Xanthomonas oryzae pv.oryzicola(Xoc),is a destructive bacterial disease in rice growing areas and is currently most common in southern part of China.At present,there is a lack of effective disease-resistant varieties and thus chemical pesticides like zinc and copper are used for the control of bacterial leaf streak.The use of chemical pesticides causes environmental pollution problem and are persistent in the plant.To excavate effective microbial resources in the soil for the control of bacterial leaf streak,a total of 249 soil samples were collected in this study.By using the wild type Xoc strain RS105 as the target bacteria,38 strains of Pseudomonas with antagonistic activity on RS105 were isolated.Strain 1257 was identified as Pseudomonas entomophila through the morphological,physiological,biochemical and molecular tests.Bacteriostatic and biochemical tests showed that 1257 could specifically antagonize Xoc and Xoo,has proteolytic enzyme activity,and could produce trace amounts of siderophore.Greenhouse experiments showed that 1257 could control the BLS with control efficiency of 35%-55%.Bioinformatics analysis showed that there are eight secondary metabolite-synthesize gene in the 1257 genome.Further,the use of Tn5 Transposon-mediated mutant library screening and functional complementation experiments of mutant genes proved that car A,car B,pur F and ser C are important functional genes that antagonize Xoc RS105.In addition,28 strains of Bacillus with antagonistic activity were isolated in this study.Strain 504 was identified as Bacillus velezensis and strain 512 was identified as Bacillus cereus,respectively.Bacteriostatic and greenhouse experiments showed that strains 504 and 512 could inhibit Xanthomonas oryzae,and have the most significant antagonism effect on Xoo.In high-susceptible rice variety Yuanfengzao,strain 512 had a significant inhibitory effect on the water-soaked symptoms caused by the bacterial leaf streak in rice leaves.These studies provide a theoretical foundation for the development of biocontrol agents of Xanthomonas oryzae and provided useful clues for the analysis of biocontrol mechanisms of Pseudomonas entomophila.