Growth Inhibition of Soil Fungi by Insecticides and Annulment of Inhibition by Yeast Extract or Nitrogenous Nutrients

Abstract

SUMMARY: Seventeen fungal species from Wisconsin prairie soils were grown on Czapek nutrient media that had been treated with the insecticides aldrin, lindane, parathion, phorate or carbaryl. All five insecticides inhibited to some extent the growth of most fungal species; this inhibition was a result of a particular insecticide-fungus combination. Threshold concentrations of insecticides, at which no decrease in growth of Aspergillus fumigatus or Fusarium oxysporum occurred, differed for each insecticide and also for each of the two fungi. Since most of the insecticides had some fungicidal effect, it was not surprising that none of the 17 fungi was able to utilize any of the insecticides as a carbon or phosphorus source. Carbaryl or aldrin at 20 μg./ml. inhibited growth of F. oxysporum by 37 to 44 %. However, the addition of yeast extract, asparagine, ammonium sulphate, ammonium nitrate or ammonium sulphamate to the culture media resulted in a complete suppression of the growth inhibitory effect of carbaryl and that of aldrin to a large extent. Replacement of yeast extract with a vitamin mixture had no effect; fungal growth was still inhibited.