Abstract: In a pot experiment, the effects of bio-control bacterial strains Paenibacillus polymyxa and Bacillus subtilis on the microbial community structure in the rhizosphere soils of cucumber and tomato were examined by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Principal component analysis (PCA) of DGGE banding patterns indicated that the effects of the two bacillus strains varied with cropped plants. In the rhizosphere soil of cucumber, no significant effects were observed on the structures of bacterial and fungal communities, but that of fungal community changed obviously with sampling time; while in the rhizosphere soil of tomato, the structure of bacterial community was less affected but changed obviously with sampling time, and the structure of fungal community was significantly affected. It was suggested that vegetable species was the major factor determining the microbial community structure in rhizosphere soil. Inoculation with test two bio-control bacterial strains had little effects on the structure of bacterial community, but its effects on fungal community structure differed with vegetable species.

Key words: Productivity, Crop-fruit ecological agriculture, Loess Plateau