INHIBITION OF SALVINIA (SALVINIA-MOLESTA MITCHELL) BY PARTHENIUM (PARTHENIUM-HYSTEROPHORUS L) .1. EFFECT OF LEAF RESIDUE AND ALLELOCHEMICALS

Parthenium (Parthenium hysterophorus L.) leaf residue (LP, leaf powder ) inhibited salvinia (Salvinia molesta Mitchell) biomass and the numbe r of healthy fronds at 0.25% (w/v) and killed the treated plants at an d above 0.75% (w/v) in about 5-15 days, depending on the quantity of t he residue. At the lethal dose, the LP caused an abrupt desiccation of above-water plant parts, probably due mainly to root dysfunction. Thi s was concurrent with the loss of dehydrogenase activity in, and an in crease in solute leakage from, the roots and loss of chlorophyll a, b, and total chlorophyll contents in the fronds, resulting in death of t he treated plants. The LP appears inhibitory to salvinia through affec ting macromolecules-proteins, lipids, and nucleic acids. The inhibitor y activity of LP at the lethal dose suspended in water was completely lost when allowed to stand for 30 days under outdoor conditions and pr omoted growth of the salvinia plants placed in it, The standard allelo chemicals, including those present in parthenium LP, except parthenin and p-hydroxybenzoic acid, did not inhibit growth up to 100 ppm. Howev er, parthenin and p-hydroxybenzoic acid killed salvinia plants at 100 and 50 ppm, respectively. Since p-hydroxybenzoic acid is unlikely to b e present at such a high concentration, parthenin appears to be one of the main allelochemicals responsible for the inhibitory effect of par thenium leaf residue on salvinia.