Field and laboratory studies for evaluating the toxicity of the insecticide Reldan on soil fungi

The response of soil fungi to the insecticide Reldan (chlorpyrifos-methyl) was studied under field and laboratory conditions. The colony forming units (CFU) of fungi were determined by means of serial dilution technique after 1 day, 7, 14, and 28 days of the insecticide application in soil. The plate count data indicated that the insecticide affected the number of fungi in treated soil compared with the untreated soil; the developed colonies decreased after 1–7 days of insecticide application and then increased with increasing application time. The effect of different concentrations of insecticide on the morphological features and sporogenesis of Aspergillus flavus, Fusarium culumorum, and Drechslera biseptata was studied. Relative conidiospore formation was sharply decreased and the conidiophores were deformed in A. flavus, while F. culumorum and D. biseptata failed to produce conidiospores, although chlamydospores were formed in large numbers when cultivated on the growth medium containing insecticide.