Isolation and identification of an endophytic and antagonistic bacterium from rice roots

Abstract:

[Background] Endophytic bacteria in crop roots are beneficial to fix nitrogen, secrete hormones and produce resistant substances to pathogenic fungi. The isolation and application of endophytic bacteria in roots has become one of the hotspots in environment-friendly prevention and control technology. Although the rice planting area in saline alkali soil is increasing, the isolation and application of endophytic bacteria from rice roots in saline-alkali soil are still limited. [Objective] To isolate endophytic bacteria from rice roots in saline-alkali soil in Daqing, to screen promoting-growth bacteria with antagonistic effect on plant fungal diseases, to investigate its bacteriostasis and promoting-growth effect, and to provide the bacteria resources for further studies on bacteriostasis and promoting mechanism. [Methods] Sterilized the root surface and then grinded the rice root, which were used to isolate the endophytic bacteria. Screened endophytic antagonistic strains and determined the ability of endogenous bacteria to secreting indole-3-acetic acid (IAA) by using confrontation culture method and modified Salkowski colorimetry method, respectively. The taxonomic status of the strains with broad-spectrum bacteriostatic effect was determined by using morphological identification, Gram staining, physiological and biochemical analysis, phylogenetic analysis of 16S rRNA structural genes and srfA/ituA/fenB functional genes. [Results] The SM13 strain was an candidate of endophytic bacterium isolated from rice roots, which showed broad-spectrum bacteriostatic effect. The bacteriostasis rates for Curvularia lunata, Sclerotinia sclerotiorum (Lib.) de Bary, Magnapporthe grisea, and Fusarium graminearum Schw were 59.38%, 78.13%, 53.12% and 37.50% respectively, and the ability to secrete IAA was 5.56±0.41 μg/mL (n=6). SM13 strain was identified as Bacillus subtilis by morphological, physiological and biochemical tests and phylogenetic analysis. The strain grew well in NA medium under pH 11.0 and salt concentration 10% condition, so it had higher salt tolerance and alkalinity tolerance. [Conclusion] The rice roots endophyte SM13 has the ability of tolerance to saline-alkaline, promoting-growth and biocontrol. It could be used as the material of microbial pesticides and biofertilizers.