ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 73 Number 2
Toxicity of three pesticides to several rice-field cyanobacteria
Ten species of heterocystous cyanobacteria belonging to five genera, viz. Anabaena, Nostoc, Calothrix, Scytonema and Westiellopsis, were isolated from costal rice fields. Orissa State, India and their relative tolerance to Sevin (carbaryl 50% WP) Rogor (dimethoate 30% EC), and Hildan (endosulfan 35% EC) was determined. The 10 species differed widely with respect to their tolerance to the pesticides; variation in the tolerance level to a specific pesticide existed among species of the same genus and also between genera. Through some of the species belonging to the genera Calothrix and Scytonema, which possess a sheath layer around their trichome, were comparatively more tolerant to the pesticides, the presence of additional cell envelope layers was not always found to be the only factor responsible for their tolerance to higher levels of the pesticides. Although the application of the recommended rates of these pesticides may not significantly reduce the growth of the cyanobacteria, higher levels, e.g., double the levels of Sevin and Hildan, in particular, can exceed the EC50 level of most of the cyanobacteria studied.
Keywords: Pesticides; Cyanobacteria; Rice field; Relative tolerance; Ensheathed forms