Differential Effects of Agricultural Pesticides Endosulfan and Tebuconazole on Photosynthetic pigments, Metabolism and Assimilating Enzymes of Three Heterotrophic, Filamentous Cyanobacteria

Cyanobacteria are present abundantly in rice fields and are important in helping to maintain rice field fertility through nitrogen fixation. Application of agricultural pesticides for improving crop productivity has become necessary in the present day agricultural practices. This has resulted in either stimulatory or inhibitory effects on the soil microflora including nitrogen-fixing cyanobacteria. The response of three nitrogen fixing cyanobacterial species to two pesticides (Endosulfan, an insecticide and Tebuconazole, a fungicide) was hence selected. A tremendous reduction in the photosynthetic pigments, metabolic as well as enzymatic activities of all the three organisms in response to the pesticides was recorded after sixteen days. All the pigments, metabolites and enzymatic activities of Anaabena fertilissima, Aulosira fertilissima and Westillopsis prolifica were dropped by between 59 to 96% upon various doses of pesticide treatments. The results showed that An.fertilissima was more tolerant to both the pesticides, whereas between the two tested pesticides, Tebuconazole found higher toxicity to Aul. fertilissima and W. prolifica.