LAUSR

ABSTRACT Soil microbial communities are crucial to the functioning of agricultural systems but little information is available on the effects of allelochemicals on soil microorganisms in vivo. Cucumber seedlings grown in soil were treated with different concentrations of vanillin (0.02–0.2 μmol/g soil), a phenolic compound with autotoxic activity. The community structures and abundances of Fusarium and Trichoderma spp. in cucumber rhizosphere were analyzed by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis and quantitative PCR, respectively. Results showed that vanillin changed the community structures of Fusarium and Trichoderma spp. Vanillin decreased the number of bands of Fusarium spp., but increased the number of bands, Shannon–Wiener and evenness indices of Trichoderma spp. (p < .05). Vanillin at all concentrations promoted the abundances of Fusarium and Trichoderma spp. (p < .05), and this stimulating effects increased with increasing concentration of vanillin. Overall, this study provided primary evidence that vanillin changed the community structures and abundances of Fusarium and Trichoderma spp., and that these two microbial groups showed different responses to vanillin.