Allelopathic effects of Acacia nilotica leaf residue on Pisum sativum L.

A greenhouse pot experiment was conducted to assess the allelopathic effects of Acacia nilotica leaves on the growth and metabolic activities of 45-day-old pea (Pisum sativum L.) plants. Qualitative and quantitative HPLC analysis of water extract of Acacia nilotica leaves revealed that protocatechuic and caffeic acids were the principal phenolic compounds accompanied by major amounts of ferulic, cinnamic acids and apigenin; whereas, pyrogallic, p-coumaric, syringic acids and coumarin were found in trace amounts. The lower doses of Acacia leaf residue (0.25 and 0.5 %, w/w) stimulated the growth of pea shoot and root, but the higher doses (0.75, 1.0, 1.5 and 2 %, w/w) were inhibitory to seedling growth and the effect was concentration dependent. The total phenolic content of pea shoots (particularly phenolic glycosides), increased at lower doses of Acacia residue and decreased with higher ones While, the phenolic aglycones increased with higher doses than lower ones. Chlorophyll a, b and carotenoids accumulated in pea shoot at lower doses of Acacia leaf residues, accompanied by accumulation of total sugar, mainly the insoluble fraction. On the other hand, the inhibition in the contents of photosynthetic pigments at higher doses of Acacia residues was paralleled by significant reduction in all sugar fractions. The contents of total nitrogen and phosphorus (their insoluble forms), increased with lower Acacia residues (0.25 and 0.5 %); whereas all nitrogen and phosphorus fractions declined by increasing Acacia doses up to 1 %. The total nucleic acids, including DNA and RNA increased with lower Acacia residue doses and gradually declined with the increase in Acacia level up to 1 %.