PURPOSE:To provide a novel microorganism useful for the growth of healthy seedling of beet and a process for the use of the microorganism. CONSTITUTION:This novel antagonistic bacterial strain SB-K88 is useful for the growth of healthy beet seedling, free from pathogenicity to beet and belongs to the genus Xanthomonas. This invention also relates to its cultured product and its treated material. The damping-off of seedling can be controlled and the initial germination is improved to enable the growth of a healthy seedling by treating seed of beet with the novel antagonistic bacterium SB-K88, its cultured product or its treated material.