Abstract: In this study, a bacterial isolate ST15 was isolated from the rhizosphere soil of pear trees, which has strong antagonistic activity against Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc), and the antibacterial circle diameters were 1.50—3.97 cm. Based on the colonial and cellular morphology, physiological and biochemical characteristics, partial nucleotide sequences of 16S rDNA and gyrB gene, the isolate was identified as Bacillus altitudinis. The sterile filtrate of ST15 had strong antagonistic activity against Xoo and Xoc, and its antagonistic activity was 1.54—1.64 times that of 1 mg/mL zinc thiazole solution and 1.32—1.52 times that of 10 μg/mL benziothiazolinone solution, respectively. The secondary antibacterial substances of ST15 showed good stability to high temperature, protease, pH (3.0—11.0) and ultraviolet light treatment. In addition, ST15 can significantly promote the growth of rice roots (P＜0.01), and had strong tolerance to zinc thiazole, benziothiazolinone and trichloroisocyanuric acid which were the main chemical bactericides against rice bacterial leaf streak and bacterial leaf blight. Field test showed that when applied ST15 biocontrol agent twice continously at a dose of 15 L/hm², the control efficacy against rice bacterial leaf streak was(63.51±3.28)%, which was equal to that of the chemical bactericide 3% benziothiazolinone suspension. To sum up, B. altitudinis ST15 is a promising biocontrol bacterium for the control of rice bacterial leaf streak and bacterial leaf blight.

Key words: Bacillus altitudinis, Xanthomonas oryzae, biological control, growth promotion