Screening Endophytic Bacteria For Control Rice Bcterial Leaf Blight

A total number of 1057 endophytic bacterial strains were obtained from surface-sterilized roots, stems, leaves or sheathes of healthy rice plants collected from provinces including Hubei, Henan, Shandong and Fujian. The isolation frequency varied with rice tissues sequenced by stem (14.2%) < leaf (21.2%) < sheath (29.9%) < root (35.6%).Three in vivo screenings on rice plants in greenhouse experiments and outdoor experiments, 4 bacterial strains, designated as MB-1-6-6, MB-1-6-5, MB-2-2-4and MB-1-1-102, were selected. They showed a significant effect on suppression of rice bacterial leaf blight (Xanthomonas oryzae pv. oryzae, XOO) with the relative efficacy of 69.3%, 56.2%, 41.2% and 36.8%, respectively, in the outdoor screening experiment.The four bacterial strains were characterized for their taxonomic identities by observing morphology of bacterial cells and colonies and detecting physiological/biochemical features, together by analyses of their 16S rDNA sequence. The strains MB-1-1-102 and MB-1-6-5 were identified as Microbacterium sp. and Stenotrophomonas sp., respectively, whereas the strains MB-1-6-6 and MB-2-2-4 were identified as Enterobacter spp.In vitro antagonistic tests showed that the 4 bacterial strains did not show any antibiosis against 9 plant pathogenic fungi. Except for the strain MB-1-6-5, the other three bacterial strains did not produce any antagonistic effect on XOO. Inoculation of the strain MB-1-6-5 on rice leaves yielded disease symptoms, whereas the other three bacterial strains were avirulent to rice.The strain MB-1-6-5 could promote development of the lateral roots for rice. Under the outdoor conditions, the four selected bacterial strains showed a stable control effect against infection of rice by XOO with the relative efficacy ranging from 73% to 87. Inoculation of rice with the bacterial cells of each of the four selected bacterial strains yielded effective control against XOO and the control effect was 32-84%. Treatment of rice with cultures (bacterial cells and metabolites) of the strains MB-1-1-102 or MB-1-6-5, but not the strains MB-1-6-6 or MB-2-2-4, was effective for suppression of XOO, with the efficacy of 77.5% for MB-1-1-102 and 83.4% for MB-1-6-5. Treatment of cell-free cultural filtrates of the strains MB-1-1-102 or MB-1-6-6 produced weak suppressive effect on XOO with the efficacy of 30.9% for MB-1-1-102 and 32.8% for MB-1-6-6. Inoculation of the combined cultures of MB-1-6-5 and MB-1-6-6 showed 23.6% of efficacy against XOO, and other strain combinations did not have any suppressive effect on XOO. Additionally, coating rice seeds with bacterial cells of each strain showed control effect on XOO with the efficacy ranging from 33% to 47%.The results obtained in this study laid a solid foundation for exploitation of the endophytic bacteria to control rice bacterial leaf blight caused by XOO in the future.