Chronic toxicity of a triazole fungicide tebuconazole on the growth and metabolic activities of heterocystous, nitrogen-fixing paddy field cyanobacterium, Westiellopsis prolifica Janet.

This study explored the chronic and harmful effects of different doses of the triazole fungicide, tebuconazole, on the growth, and metabolic and enzymatic variations in the filamentous paddy field cyanobacterium, Westiellopsis prolifica Janet. The growth of the cyanobacterium was determined by an estimation of the change in pigment contents. Chlorophyll-a, carotenoids and accessory pigments such as phycocyanin, allophycocyanin and phycoerythrin, were shown to decline over a 16-day period by a factor of 92%, 93%, 83%, 95% and 100%, respectively, with increasing doses of the fungicide. Metabolic and enzymatic activities were also adversely affected. Over the 16 days, a gradual rise in the total phenol content was recorded when Westiellopsis prolifica Janet was treated with 60 ppm of the fungicide, despite the reduction in carbohydrates, proteins and amino acids by 96%, 92% and 90%, respectively. Moreover, the enzymes nitrate reductase (NR), glutamine synthetase (GS) and succinate dehydrogenase (SDH) also registered reductions of 93%, 90% and 98%, respectively. This study indicates that tebuconazole, although an important fungicide used extensively in rice fields, exhibits an inhibitory effect on the growth and metabolic activities of Westiellopsis prolifica Janet and hence possibly on other varieties as well.