The experiment was conducted to observe the inhibitory effects of the leaf extract derived from neem (Azadiracta indica) on germination and growth behavior of some cowpea varieties (receptor). Experiments were set on sterilized petridishes with a photoperiod of 24 hours at room temperature of 27-30 o C. The effects of the different concentrations of aqueous extracts were compared with distilled water (control). The aqueous extracts of leaf caused significant inhibitory effects on germination, root and shoot elongation and development of lateral roots of treated plants. Bioassays indicated that the inhibitory effect was proportional to the concentrations of the extract, as concentration increased the extent of inhibition also increased. The study also revealed that inhibitory effect was much pronounced in root and lateral root development rather than germination and shoot growth.
The preliminary Phytochemical investigations and phytotoxic effects of aqueous leaf extracts of Albizia lebbeck on Sorghum bicolor was assessed. The result from phytochemical screening revealed that all the allelochemicals tested where found present except steroids and phlobatannins when petroleum ether, methanol and water extracts were used. Petroleum ether extract show the presence of amino acids, protein and glycosides while methanol and water extracts showed their absence. Alkaloids, anthraquinones and acids were found present when methanol was used and absent using petroleum ether and water extracts. These allelochemicals are all important allelopathic sources. The leaf extract slowed down the rate of growth of the radicle and plumule of Sorghum bicolor seeds when compared to control. But these inhibitions were not significantly different at 5% level. The degree of inhibition increased with increase of concentration of the extracts hence inhibitions were prominent at extract of higher concentrations.
A laboratory experiment was conducted to assess the effects of allelochemicals of Eucalyptus camaldulensis, Eucalyptus citriodora and Eucalyptus globules on germination and root elongation using leguminous crop ground nut ( Arachis hypogea) as bioassay material. The experiments were conducted in sterilized petridishes. The effect of different concentration of aqueous extracts was compared with distilled water (control). The result revealed that different concentrations of E. globulus and E. camaldulensis extracts caused highly significant (p=0.05) inhibitory effect on germination and root elongation. The bioassays indicated that the inhibitory effect was proportional to the concentrations of the extracts so that higher concentration has a stronger inhibitory effect. The study also revealed that inhibitory effect was much pronounced in root development rather than seed germination.
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