PHYTOTOXICITY OF SESQUITERPENE LACTONE PARTHENIN ON AQUATIC WEEDS

The sesquiterpene lactone parthenin, one of the major toxins in an obn oxious weed, parthenium (Parthenium hysterophorus L.), was toxic at 50 ppm to the floating aquatic weeds pistia (Pistia stratiotes L.) and l emna (Lemna pausicostata Hegelm.) and at 100 ppm to water hyacinth (Ei chhornia crassipes Mart Solmns.), salvinia (Salvinia molesta Mitchell) , azolla (Azolla nilotica Decne.), and spirodella (Spirodella polyrhiz a L. Schleid). The lethal dose for the submerged weeds najas (Najas gr aminea Del.), ceratophyllun (Ceratophyllum demersun L.), and hydrilla (Hydrilla verticillata L. f. Royle) was 25 ppm. The submerged aquatic weeds were more sensitive to parthenin. Water hyacinth was used as a r epresentative for studying the phytotoxicity of pathenin on aquatic we eds. Inhibition of water hyacinth by parthenin was associated with dec line in water use, root dysfunction, excessive leakage of solutes from roots indicative of massive damage to cellular membranes, loss of deh ydrogenase activity in the roots, and loss of chlorophyll in the leave s. Plant death occurred in a period of one to two weeks. Parthenin phy totoxicity is gradually lost in an aquatic environment as a lethal dos e became nonlethal in about 30 days under outdoor conditions. Possible buildup of a toxin concentration may affect population dynamics and a shift in the aquatic weed flora in the immediate area of parthenium s tands. Accumulation of the toxin in an aquatic environment, however, a t a level sufficient to produce such changes in a natural ecosystem as a consequence of rain washing parthenium plants and leaching of toxin from their residue appears to be unlikely.