Abstract:Bacillus subtilis XF-1 had good control effects on clubroot of Chinese cabbage both in the greenhouse and in the field plots. Colonization dynamics and the impact factors of XF-1 by biotics marker and pot-culture were studied to understand the bacterial control mechanism and provide the theoretical basis of commercialization. The greenhouse experiment results indicated that it could colonize in the rhizosphere, root surface and root of Chinese cabbage successfully. The survival number of B.subtilis XF-1 in the rhizosphere and root surface remained 103 CFU/g soil and 102 CFU/g inside the root after inoculation of 60 days. The trend of colonization in rhizosphere and root surface increased first, then decreased and increased again and finally stabilized. The trend of colonization inside the root was rising and then falling. The 15-day-old root of Chinese cabbage was used to make paraffin section and observed the bacterium under microscope. The results showed that XF-1 cells were observed in parenchyma and trachea of the root, its ability of colonization was affected by temperature, concentration, media and soils. Its colony number in sterilized soil was more than that in natural soil. The higher its suspension concen tration, the more colony number was. XF-1 could colonize in Chinese cabbage rhizosphere with 105 CFU/g soil after 28 days in 16 ℃ incubator. The colony number of Chinese cabbage rhizosphere was higher when potato juice sucrose (PS) was used than that when potato juice dextrose (PD) as a medium. XF-1 could also colonize in the rhizosphere of maize.