Soil Microorganisms

DNA probes for identifying Verticillium dahliae were selected from genomic DNA of an isolate of V. dahliae TV103 pathogenic to tomato by differential hybridization. The fungal DNA was digested with EcoRI, followed by ligation to pUC18 and was used to transform Escherichia coli. Four recombinant plasmids that hybridized to V. dahliae DNA but not to the DNAs of other fungi, including V. albo-atrum and Fusarium oxysporum were selected as probes by dot blot hybridization. Two of the probes specifically hybridized to the DNAs from all the isolates of V. dahliae and the other two probes were specific to the isolates pathogenic to tomato (tomato pathotype). Southern hybridization indicated that the latter two probes showed unique banding patterns for the isolates of the tomato pathotype. Analysis of these fragments provided one small DNA fragment, designated as S4, which was highly specific to the tomato pathotype of V. dahliae, suggesting that the S4 fragment could become a useful tool for the identification of V. dahliae isolates pathogenic to tomato.

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In order to examine the soil microbial activity of soils in an urban area, β-glucosidase activity, soil respiration rate and the amount of microbial biomass carbon were measured in soils from four parks in Kobe City. The soils were collected from three stands, bare ground, turf and forest, according to the land-use type. Soil microbial activity bases on the determination of the β-glucosidase activity and soil respiration rate, and the amount of microbial biomass carbon were highest in the forest soils, followed by the turf soils. The bare ground soils in all the parks showed a low activity and low values for microbial biomass carbon. Furthermore, the effects of the relative age of the parks on soil properties were examined in three parks, which had the same parent materials. In the bare ground soils, the microbial activity and the amount of microbial biomass carbon were the lowest, and did not change with time. In the turf soils, the values increased gradually with time. In the forest soils, these values significantly increased after about twenty years. It was found that the soil microbial activity and the amount of microbial biomass carbon in an urban area were affected by the land-use type, and that the activity and amount of biomass showed differences in the variation pattern according to the land-use type.

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