THE EFFECTS OF THREE PHENOLIC COMPOUNDS ON LEMNA GIBBA L. PERFORMANCE: A NEW ALLELOPATHY BIOASSAY

Abstract

Lemna gibba L. (duckweed) characterized by its gibbosity or swollen fronds on the abaxil side was used as a bioassay organism to test the allelochemical effects of salicylic acid, ferulic acid and umbelliferone. Growth rate (K) of individual fronds, biomass production or dry weight (DW) and chlorophyll production were the parameters measured. A bioassay procedure using 50 ml of E medium with and without sucrose in 125-ml Erlenmeyer flasks plus the selected concentration of allelochemical was developed. After 7 days growth, parameters were evaluated. L. gibba was affected by the 3 compounds. Salicylic acid affected the plant at concentrations as low as 0.02 mM causing stimulation of K and chlorophyll production, while the DW production was inhibited. Higher concentrations inhibited all the parameters. Ferulic acid and umbelliferone began affecting L. gibba at 0.10 mM, causing stimulation of the arameters up to the 1.00 mM concentration where inhibition was apparent. The addition of organic sources (sucrose and tartaric acid) reduced the sensitivity of L. gibba to the allelochemicals. L. gibba was found to be a sensitive organism for use in the bioassays to detect allelopathic effects.