Effect of selected herbicides on growth and lipid content of Nannochloris oculata

Nannochloris oculata (Droop) D.J. Hibberd has attracted attention as a potential source of biofuels because of high oil content and rapid growth rate. The effect of selected herbicides on algal growth and total lipid content was examined. Twenty-two herbicides representing 14 modes of action were assayed. Photosystem II inhibitor diuron was the most toxic herbicide to algal growth. At low concentrations, sethoxydim was not toxic to algae but decreased its lipid content significantly. Photosystem I inhibitor diquat at low concentration did not affect algal growth, but algal growth inhibition increased with increasing concentration. Diquat at 0.1 and 1 mg L^-1 decreased lipid content to 8.66 and 8.53%, respectively. At 5 mg L^-1, glyphosate stimulated algal growth but decreased lipid content to 5.60% of dry weight. S-metolachlor had a significant effect on both algal biomass and lipid content. 5-metolachlor at 0.1 mg L^-1 decreased algal biomass to 75% of untreated control and decreased lipid content from 13.33 to 6.21% of dry weight. Fluridone at 0.1 mg IT¹ decreased algal biomass to 84% of untreated and completely killed algae when the concentration increased to 1 mg L^-1. Simazine at 0.1 mg L^-1 had no significant effect on algal growth but decreased lipid content from 13.33 to 5.15% of dry weight. Pendimethalin and dinoterb had no significant effect on algal growth but reduced lipid content to 6.19 and 6.03%, respectively. The use of algae as a source of fuel will undoubtedly require the use of outdoor, open-pond systems. These results will be useful for developing management systems to control invasive algal species in outdoor, open-pond systems, ultimately keeping the oil-producing algae pure.