Effects of three phenolic compounds onLemna gibba G3.

Lemna gibba L. G3, (duckweed) was used as a bioassay organism to test the allelochemical effects of salicylic acid (SA), ferulic acid (FA), and umbelliferone (UM). Growth rate (K), dry weight (DW) and total chlorophyll (CHL) production were measured after seven days of growth. The bioassay procedure used 50 ml of E medium with and without sucrose in 125-ml Erlenmeyer flasks plus the selected concentration of allelochemical. At concentrations of 50 μM and greater, SA caused inhibition of K and DW production inL. gibba G3, while the threshold for CHL reduction was 20 μM. FA inhibited the DW and CHL production at 100 μM when the compound was auto-claved in E medium containing sucrose. Treatments of UM were least toxic with an inhibition threshold of 500 μM for K and DW production in medium without sucrose. UM did not reduce CHL production until 750 μM. In some cases, different thresholds of inhibition were observed depending on the presence or absence of sucrose and tartaric acid in the medium, and whether or not the chemicals were autoclaved with the medium.