Exploring possibility of controlling Microcystis population using terrestrial plant extracts and indigenous technologies

Algaecide property of leaf aqueous extracts (LAEs) of three plants viz., Azadiracta indica, Tridax procumbens, Calotropis procera as well as two indigenous technologies (ITKs) viz., application of neem oil and cow urine were evaluated against wild Microcystis bloom and pure culture of Microcystis aeruginosa in laboratory. Five treatments were designated as LAE of A. indica (T-1), neem oil (T-2), LAE of T. procumbens (T-3), LAE of C. procera (T-4) and cow urine (T-5). Inhibitory effects of these agents were studied in terms of colonial morphological alterations in bloom and reduction of cell density in pure culture. Cell density of 2.0 x 105 cells ml-1 was achieved through inoculation of Microcystis from pure culture and each inhibitor was added at 50 ml l-1 to the flasks. All flasks were maintained for 14 days at 300C with continuous aeration and illumination (2000 Lux). After 14 days, cow urine (T-5) showed the highest cell inhibition (87.3%) followed by T-1 (82.7%) and T-3 (61.6 %) (p<0.05), whereas there were 82, 259 and 371% rise in the cell density in T-2, T-4 and control, respectively, compared to the base population seeded on day-0. Indirect measurement through daily record of absorbance in treatments at 680 nm also revealed the growth rate to decrease in the order, control>T-4>T-2>T-3>T-1>T-5. Keywords: Algal bloom, Algaecide property, Leaf aqueous extracts, Microcystis aeruginosa, Terrestrial plants