Toxicity of a rice field herbicide in some nitrogen-fixing algae

The incorporation of diquat into cultures of Nostoc muscorum and Cylindrospermum sp. Proved to be highly toxic. The range of various concentrations employed varies from 1 microgram/ml 15 micrograms/ml. Relatively higher does (above 5 micrograms/ml) reduced the chlorophyll a content and a progressive decrease in algal growth and ultimately complete lysis of the cells was recorded with the increasing level of the herbicide. A concentration of 15 micrograms/ml has been found to be algicidal for both the test organism.