Degradation of dyfonate in soil inoculated with Rhizopus arrhizus.

Abstract

The fungus Rhizopus arrhizus, capable of degrading the soil insecticide Dyfonate in shake cultures, was added to a 14C-Dyfonate-treated soil (Piano silt loam) to test its capability to degrade the insecticide in a soil environment. Scanning electron microscopy showed that this soil was a poor substrate for the growth of microorganisms and that the fungus grew well only when a glucose-containing nutrient medium was added to the soil. It was under these conditions that 14C-Dyfonate was degraded during a 21-day incubation period as indicated by a recovery of only 12% of the applied insecticide, by the production of its oxygen analog, dyfoxon, and by the appearance of significant amounts of water-soluble metabolites (11% of the applied 14C). Inoculation of soils with fungal spores in water also resulted in a metabolism of the insecticide, but at a slower rate. The addition of nutrient media, but no fungal spores, to Dyfonate-treated soil, enhanced the growth of naturally occurring microorganisms and resulted in some degradation of the insecticide.