The Effect of Bipyridyl Herbicides on the Loss of Nutrients from Fungi

Paraquat and diquat cause rapid loss of potassium and phosphate from Aspergillus niger, Penicillium frequentans, Mucor hiemalis and Zygorrhynchus heterogamus. The rate of loss is greater at higher concentrations of herbicide, particularly from Zygorrhynchus and Mucor. A brief incubation in paraquat or diquat is followed by sustained loss of potassium when colonies of the four species are transferred to water. Sodium azide also stimulates loss of potassium but this ceases when colonies are transferred to water. Paraquat enhances the level of malondialdehyde, a breakdown product of membrane fatty acids, in Zygorrhynchus and Mucor. These results are discussed with reference to the possible mode of action of bipyridyl herbicides in fungi.