Interference of aquatic plants associated with wild rice (Zizania palustril L.)

Abstract

The objective of this thesis was to determine the interference potential of aquatic plants to wild rice (Zizania palustris L. ) through field and laboratory studies. Three companion papers describe the influence of aquatic plants on growth of wild rice; the allelopathic potential of aquatic plants and the isolation and identification of allelochemicals from two selected plants. The growth of wild rice in the presence cind in the absence of different plemt species, namely Eleocbaris smallii, Scirpus acutus, Equisetum fluviatile, Nymphaea odorata, Nupheur variegatum, Sparganium fluctuans, ttyriophyllum verticillatum and Potamogeton natans was studied. Number of wild rice plants and their growth decreased in the presence of different plant species. Environmental factors had no influence on the growth of wild rice, either in the presence or absence of different species. It is suggested that the adverse effects of different species on wild rice may be due to either their early growth habit, shading the wild rice plant, or to their allelopathic effects. The allelopathic potential of the above mentioned plant species was examined using lettuce and wild rice seedling bioassays. The root length of lettuce and the total root length of wild rice seedlings were significantly reduced by aqueous extracts of these plant species. The lettuce seedling bioassay was more responsive than that of wild rice. Shoot growth was less affected. Bioassay with an aqueous extract of lake sediments associated with these species had little inhibitory effect on growth of wild rice seedling. The use of teurget species as a bioassay material and further studies on phytotoxic effect of lake sediments have been emphasized for evaluating their ecological significemce. The phytotoxic compounds from water extracts of the rhizome of Scirpus acutus and the shoot of Eleocbaris smallii were isolated by ethyl acetate extraction emd identified by GC-Mass spectroscopy. The ethyl acetate organic fraction of water extract of Scirpus rhizomes contained lactic, succinic, fumaric, 2-hydroxy succinic, 2-phenyl lactic, m-hydroxy benzoic, p-hydroxy benzoic, protocatechuic, dehydroêüaietic and ferulic acids; p-hydroxy benzyl alcohol, p-hydroxy phenyl ethanol and a dye, catechin. The organic fraction of the extract of Eleocbaris shoots contained 4-methoxy phenol, benzofuran, benzene acetic acid, l-hydroxy-5-methyl acetophenone and 1,3,4-dimethoxy phenyl ethanone. The growth inhibiting properties of some of these compounds under field conditions are discussed.