Inhibitory effect of parthenium (Parthenium hysterophorus L.) residue on growth of water hyacinth (Eichhornia crassipes Mart Solms.) I. Effect of leaf residue

The allelopathic effect of parthenium (Parthenium hysterophorus L.) leaf residue (dry leaf powder, DLP) on water hyacinth (Eichhornia-crassipes Mail Solms.) was studied. The treatment caused wilting starting from the margins of the older leaves and desiccation of above-water plant parts (shoot). Appearance, persistence, and disappearance of symptoms depended on the level and duration of the treatment and recovery of the treated plants, if it occurred. The treatment drastically reduced the number of healthy leaves (HLN) add the plant biomass at 0.25% (w/v) DLP; the treated plants recovered in about one month. At and above 0.50% (w/v) DLP, the plants were killed in about one month, resulting in sinking of the dead mass in water. Physiological effects of the treatment included deterioration of membrane integrity, loss of dehydrogenase activity with concurrent drastic reduction or total failure of water absorption by the roots, and reduction of chlorophyll contents in the leaves. The results indicate that the inhibitors leached out of the DLP affected the water hyacinth plants through changes in macromolecules: protein, lipid, and nucleic acid, resulting in root dysfunction and other inhibitory activities both in the root and shoot. Phenolic and other inhibitors including those found in the parthenium plant (except sesquiterpene lactones which have not been tested) at 50 ppm, except p-hydroxybenzoic acid, did not affect the treated plants. Such a high concentration of the allelochemicals is unlikely to be present in the medium at the lethal dose (0.50% w/v) of the DLP. Even with p-hydroxybenzoic acid, the plants recovered subsequently and grew normally. Thus, it appears that other allelochemicals including sesquiterpene lactones were mainly responsible for the inhibitory activity of the DLP on water hyacinth plants.