Abstract: In this experiment， an endophytic bacterium named GN232 against Xanthomonas axonopodis pv. citri Xac. was isolated from navel orange and screened in plate and on leaf in vitro. And the identification and characterisics of its antibacterial active metabolites were studied. By the analyses of morphological， cultural， physiological， biochemical characteristics and 16S rDNA sequence， GN232 was indentified as Bacillus subtilis subsp. subtilis. The activity detection of its fermentation liquid indicated that the antibacterial substances were not sensitive to the temperature less than 100℃， and stable under neutral pH/trypsin， but the activity was decreased under ultraviolet radiation for 25 minutes. In addition， when the fermentation liquid was mixed with agricultural streptomycin， the inhibition effects on Xanthomonas axonopodis pv. citri were increased by 26.8% and 20.7% compared with using fermentation liquid or agricultural streptomycin separately.

Key words: endophytic bacteria, Xanthomonas axonopodis pv. citri Xac., bioactive metabolites