Abstract: The mechanism of Bacillus subtilis B5423 to suppress the occurrence of rice sheath blight is mainly by means of antibiotics produced by B5423. Under field conditions, the experiment of B5423-R(marker strain of B5423, a Rifampicin-resistant mutant ) to suppress vertical spread of sheath blight was conducted by inoculating R. solani and spraying B5423-R in different methods (including spraying times, and spraying intervals). Successive 3-4 times spraying with an interval of one day made the population sizes of B5423-R on rice stems be higher than 1×10⁶ cfu/g within 6-7 days, and significantly reduced relative lesion height (RLH) of rice sheath blight. On the other hand, successive 3- 4 times spraying with an interval of four days made B5423-R on rice stems fluctuate from 1×10⁶ to 1×10⁵ cfu/g within 15 days, and not cause any significant reduction of RLH of rice sheath blight in 25 days. The above results revealed that the population threshold of B5423-R to suppress rice sheath blight should be higher than 1×10⁶ cfu/g during the early infection of R. solani (within 6-7 days).

Key words: antagonistic bacteria, biological control, rice sheath blight, threshold population size

摘要： 在菲律宾国际水稻研究所实验农场田间条件下，通过人工接种Rhizoctonia solani,采用不同的方法(喷雾次数、间隔期)喷雾B5423-R（B5423的标记菌株，为利福平Rifampicin抗性的突变体），在接种1 d后，采用2 d喷1次、连续3～4次喷雾的方法，使B5423R在稻株上的群体数量在6～7 d内维持在1×10[sup]6[/sup]cfu/g以上，在25 d内显著地降低相对病斑高率；而采用5 d喷1次、连续3～4次喷雾的方法，B5423-R在稻株上的群体数量在15 d内维持在1×10[sup]5[/sup]～106cfu/g，在25 d内相对病斑高率未能显著降低。表明在纹枯病侵染早期的6～7 d内，在稻株上B5423R维持在1×10[sup]6[/sup]cfu/g以上是抑制纹枯病的阈值群体数量。

关键词: 拮抗细菌, 生物防治, 水稻纹枯病, 阈值群体数量