Abstract
Investigation was carried out on the phytochemical composition of methanolic and water aqueous extracts of Tithonia diversifolia and their phytotoxic effect on the growth of Sorghum bicolor (L.) Moench. The phytochemical analyses indicated the presence of bioactive substances such as alkaloids, saponins, glycosides, flavonoid, tannins, terpenoid and phenols in the methanolic extract and the later five allelochemicals in the water extract. The allelochemicals were of higher concentrations in the methanolic extract than in the water extract. The methanolic extract was found to be more phytotoxic than the water extract since the reduction of the germination percentage of the test crop was in the order of 100% methanolic extract > 50% methanolic extract >100% water extract. The germination and seedling growth inhibition was then extract concentration dependent and significant at P < 0.05. Both methanolic and water extracts have greater inhibitory effects on the growth of the radicle than on the plumule growth at 100% extract concentrations.
Highlights
The methanolic extract was more phytotoxic than the water extract and the inhibitory activity of the various extracts was concentration dependent since inhibition of these growth parameters increased as the concentration increased
The phenols content (0.31%) in the shoot of T. diversifolia at 12 weeks of growth in 100% water regime was the highest followed by alkaloids, tannins and flavonoids
The phytochemicals contents in the shoot of T. diversifolia in the 50% water regime was higher than that in the shoot of T. diversifolia grown in 100% water regime
Summary
Gray commonly referred to as Mexican sunflower is a member of the family Asteraceae It is a perennial broad-leaved weed which grows to about a height of five meters or more and varies from highly branched low population variety to unbranched high population variety. Rice (1984) and Putnam (1988) observed that chemicals with allelopathic potential i.e. allelochemicals are present in the root, rhizome, stem, leaves, flowers, inflorescence, pollen, fruits and seeds of plants. They further stated that leaves are the major sources of these allelochemicals. According to Gniazdowska and Bogatek (2005), the effects of allelochemicals action are detected at molecular, structural, biochemical, physiological and ecological levels of plant organization
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