Abstract
In vitro studies were conducted on the mode of death of Fusarium oxysporum f. sp. raphani in three kinds of soil flooded with glucose solution. A marked decrease was observed in the fungal population in each of the three soils when it was flooded with 1.8-2.4% glucose solution. The redox potential and the pH value of the soil dropped at first, and then the fungal population decreased to about one-thousandth of the initial population in infested Tsukuba soil flooded with 3% glucose solution. Fifty-five% of chlamydospores of the fungus were killed during the first 24hr of incubation, when they were seeded in the glucose-amended flooded soil preincubated for 5 days. Few chlamydospores were found alive 48hr after seeding. The centrifuged supernatant of glucose-amended flooded soil showed only a weak antifungal activity. When the chlamydospores were exposed to a head-space gas above the soil, 99% of the chlamydospores were killed during the first 2 days of exposure. The fungicidal activity of the head-space gas was approximately equal to that of the soil. In conclusion, the death of the fungus in the soil flooded with glucose solution was attributable to a volatile or evolved fungicidal substances in the soil.
