Phytochemicals and Allelopathic Effects of Aqueous Extracts of Petiveria alliacea L. on Selected Key Agricultural Weeds: Euphorbia heterophylla L. and Cyperus esculentus L. in Ibadan, Nigeria

Abstract

Allelopathy contributes to sustainable agriculture by acting as a natural herbicide or growth regulator depending on specific phytochemicals and their concentrations. Petiveria alliacea, an indigenous shrub, exhibits allelopathic potential through its bioactive compounds. This study was carried out to investigate the phytochemical composition and allelopathic effects of aqueous shoot and root extracts of P. alliacea on the germination and early growth of Euphorbia heterophylla seeds and Cyperus esculentus corms in Ibadan, Nigeria. Mature shoots and roots were soaked in distilled water for 24 h, filtered, and subjected to qualitative and quantitative phytochemical analyses. Four concentrations (100, 75, 50, and 25%) of shoot and root extracts of P. alliacea were applied to seeds and corms in Petri dishes, with distilled water as control. Germination percentage, radicle, and plumule lengths were recorded on day seven and analyzed using ANOVA (α = 0.05). Results indicated the presence of saponins, terpenoids, anthraquinones, and flavonoids in both shoots and roots, while tannins, alkaloids, phenols, and cardiac glycosides were restricted to roots. Terpenoid levels were higher in shoots, whereas other phytochemicals were more concentrated in roots. All extract concentrations significantly inhibited germination and early growth of both species. Shoot extract at 100% showed the greatest suppression, reducing germination of E. heterophylla to 30% and C. esculentus to 63%, completely inhibiting radicle and plumule growth in E. heterophylla and substantially reducing shoot and root lengths in C. esculentus. These findings demonstrate that aqueous extracts of P. alliacea contain potent inhibitory phytochemicals capable of suppressing germination and seedling development, indicating their potential as effective pre-emergence bioherbicides for sustainable weed management.