Assessment of differences in ascomycete communities in the rhizosphere of field-grown wheat and potato.

To assess effects of plant crop species on rhizosphere ascomycete communities in the field, we compared a wheat monoculture and an alternating crop rotation of wheat and potato. Rhizosphere soil samples were taken at different time points during the growing season in four consecutive years (1999-2002). An ascomycete-specific primer pair (ITS5-ITS4A) was used to amplify internal transcribed spacer (ITS) sequences from total DNA extracts from rhizosphere soil. Amplified DNA was analyzed by denaturing gradient gel electrophoresis (DGGE). Individual bands from DGGE gels were sequenced and compared with known sequences from public databases. DGGE gels representing the ascomycete communities of the continuous wheat and the rotation site were compared and related to ascomycetes identified from the field. The effect of crop rotation exceeded that of the spatial heterogeneity in the field, which was evident after the first year. Significant differences between the ascomycete communities from the rhizospheres of wheat in monoculture and one year after a potato crop were found, indicating a long-term effect of potato. Sequencing of bands excised from the DGGE gels revealed the presence of ascomycetes that are common in agricultural soils.