The chemical contents and compositions of vegetables are generally influenced during their developmental stages. It is for this reason that the research was conducted in pot experiment to investigate the effect of reproductive phase (fruiting) on anti-nutrients (soluble and total oxalates), toxic substances (cyanide and nitrate) and some micronutrients namely, vitamin C, β-carotene (provitamin A) and mineral elements (Fe, Mg, Zn, Cu, Ca, Na and K) in Vernonia amygdalina grown on nitrogen and non-nitrogen treated soil. The leaves of V. amygdalina were harvested and analysed at vegetative phase (market maturity) and reproductive phase (fruiting). Results obtained showed that the levels of cyanide, nitrate, soluble and total oxalate, β-carotene and vitamin C were significantly elevated in the reproductive phase of V. amygdalina irrespective of soil nitrogen levels, except that the elevation in β-carotene concentration was only significant in control. The concentrations of Fe, Mg, Ca and K decreased during the reproductive phase, however, the reduction of Mg was observed only with the applied nitrogen fertilizer. The concentrations of Zn and Na were not significantly affected by the reproductive phase of V. amygdalina. The results conclude that phytotoxins are concentrated more at reproductive phase than at vegetative phase in V. amygdalina.
Key words: Vernonia amygdalina, anti-nutrients, toxic substances, micronutrients, vegetative phase, reproductive phase, soil nitrogen levels.
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