Abstract
The soil distributed to the fields around Hokkaido Kitami Agricultural Experiment Station in Kitami district, Hokkaido (called Kitami soil hereafter) is suppressive to bean root rot pathogen, Fusarium solani f. sp. phaseoli. Macroconidial germination of the pathogen is strictly inhibited in the soil (Furuya and Ui, 1981). It has been suggested that both chemical and microbiological factors are involved in the inhibition as causal agents. The former is reported to be operative only under acidic conditions (Furuya, 1982). Exchangeable aluminum of the soil samples was reduced to 2.0meq/100g or less, when the inhibition is eliminated by addition of calcium carbonate. Among 15 soil samples collected from the fields around the Agricultural Experiment Station, 7 of them with less exchangeable aluminum than 2.0meq/100g did not show inhibition at all. Macroconidial germination is highly sensitive to aluminum, as it was inhibited at the concentration of 0.015meq/100ml in vitro. Manganese, another possible substance that could be toxic or inhibitory in acid soils, was not detected in Kitami soil at a concentration enough to inhibit the germination. These results suggest that aluminum toxicity plays a substantial role in the inhibition of macroconidial germination in the suppressive soil.
