Allelopathic effects of Eichhornia crassipes roots on Alexandrium tamarense.

Allelopathic effects of dry powder and acetone/ethyl acetate extract of Eichhornia crassipes roots on Alexandrium tamarense (HK strain) were evaluated. E. crassipes root powder at 0.1, 0.5, 1.0, 1.5 and 2.0 g/litre were added to flasks containing 6000 cells A. tamarense/ml. Initially, 0.01, 0.03, 0.05 and 0.07 g/litre of the extracts were placed into weighted slides. The slides were then added to the flasks containing 100 ml of A. tamarense. At the end of the experiment, the slides were removed, dried and weighed. The actual concentration of extracts in the cultures was obtained from the loss in weight. The growth of A. tamarense was absolutely inhibited when the algae was exposed to dry powder of E. crassipes roots at more than 1.5 g/litre. When the concentration of dry powder of E. crassipes roots were 0.5 and 1.0 g/litre, the growth of algae increased after 3 days. The growth of A. tamarense was also inhibited with 0.038 and 0.022 g/litre acetone and ethyle acetate extract of E. crassipes roots, respectively. It suggested that E. crassipes could be a potential algaecide to control harmful algal blooms.