RESUMO
Aqueous extracts ofNuphar lutea (L.) Sibth. & Sm. leaves (blades plus petioles) and roots plus rhizomes were tested for allelopathic activity using lettuce seedling andLemna minor L. assay systems. The 12.5, 25, 125, and 250 parts per thousand (ppt) treatments of both extracts killed the lettuce seedlings. At 2.5 ppt of extract, radicle growth of lettuce was 29% of the control for leaves and 31% of the control for roots plus rhizomes.Lemna minor frond number was reduced to 34% of the control by the 25 ppt leaf extract and to 43% of the control by the 25 ppt roots plus rhizomes extract.L. minor was killed by concentrations of 125 ppt and above of both plant part extracts. As expected, the frond number and total chlorophyll content measured by theL. minor assay were highly correlated. Osmotic potentials below 143 mOsmol/kg had no influence onL. minor growth. Neither the osmotic potential nor the pH of the undiluted extracts ofN. lutea were in the range known to influence the growth of either lettuce seedlings orL. minor. Nuphar lutea extracts were many times more inhibitory than 16 other hydrophytes we previously examined.
RESUMO
Antialgal, antibacterial, and allelopathic properties of the submersed, aquatic, dicotyledonous water shield,Brasenia schreberi Gmelin (Cabombaceae), were examined. Extracts ofB. schreberi were found to inhibit the eukaryotic alga,Chlorella pyrenoidosa, and the prokaryotic alga,Anabena flosaqua, as well as nine different bacteria. Lettuce seedling bioassay showedB. schreberi to be allelopathic. These phytotoxic properties probably contribute to the observed dominance ofB. schreberi in aquatic environments and also make it a promising candidate for allelopathic plant management of aquatic weeds.
