Dynamics of the diversity of fungal and Fusarium communities during continuous cropping of cucumber in the greenhouse

microbial community; PCR-DGGE; pot experiment; quantitative RT-PCR; soil sickness. The continuous cropping of cucumber in the same potting soils may result in a reduction of yield and quality of the crop, a phenomenon described as soil sickness. The changes of soil microbial communities as affected by continuous cropping and the link between these changes and soil sickness of cucumber are still not clear. In the present study, cucumber was cropped in pots under greenhouse conditions for nine successive cropping cycles. Structures and sizes of rhizosphere fungal and Fusarium (Ascomycota, Fungi) communities, both ubiquitous and ecologically important in soils, were analysed with PCR-dena-turing gradient gel electrophoresis and quantitative reverse transcription PCR, respectively. Cucumber showed retarded growth in the seventh cropping cycle. The RNA- and DNA-based fungal community structures derived from the same sample differed from each other, and the active soil fungal communities were more sensitive to continuous cropping. The RNA-based fungal and Fusa-rium community sizes were larger in the seventh cropping cycle than in the other cropping cycles. Overall, the findings of this study indicate that the pop-ulation sizes rather than the diversity of fungi and Fusarium communities are linked to the soil sickness associated with cucumber cultivation