Association between Spirodela polyrrhiza and blue green algae in aquatic habitats and in vitro conditions in relation to metabolite concentrations under monoculture and co-culture

Spirodela polyrrhiza samples were collected from various locations within the geographical periphery of Malda district in West Bengal, India. Samples collected from all sites were associated with algal colonies comprised of diatoms and blue green algae. Such association of different algal groups and greater duckweed in their natural habitat occurred in the lower epidermis of the fronds. Among the members of Cyanophyceae, Oscillatoria sancta was found to be abundantly associated with the fronds under in vivo conditions. To mimic the in vivo association, axenic monocultures of both S. polyrrhiza and O. sancta were maintained separately or by co-cultivation. Association with O. sancta under in vitro growth conditions prolonged the stationary growth phase of greater duckweed significantly. A growth-promoting association between the two species was shown by increased concentration of some metabolites of S. polyrrhiza. Correlation between growth of the two species were confirmed.