Evaluation of the Allelopathic Potential of Caralluma tuberculata N.E. Brown on Selected Vegetable Crops through Bioassays and Phytochemical Analysis

Abstract

Caralluma tuberculata N.E. Brown is a medicinal species valued for its pharmacological and nutritional properties. This study evaluated the allelopathic potential of C. tuberculata on selected vegetable crops using sandwich bioassays, pot experiments, and spectrophotometric analyses. In sandwich bioassays, dried plant material (0.05 and 0.10 g) was tested against Lactuca sativa, Raphanus sativus, Spinacia oleracea, Cucumis sativus, and Abelmoschus esculentus. Pot experiments employed n-hexane, acetone, and ethanol extracts at 1% and 3% (w/v) to assess seedling growth and morphology. Total phenolic and flavonoid contents were quantified and expressed as gallic acid equivalents (GAE) and quercetin equivalents (QE), respectively. The results revealed concentration-dependent inhibition of seed germination and seedling growth in most species, with significant reductions in radicle and hypocotyl lengths. Morphological abnormalities, including chlorosis, necrosis, wilting, reduced leaf production, and plant mortality, were observed. Raphanus sativus and Spinacia oleracea were the most sensitive species, whereas Abelmoschus esculentus exhibited partial tolerance and slight stimulation of hypocotyl growth under some treatments, suggesting a possible hormetic response. Phytochemical analyses confirmed the presence of phenolic and flavonoid compounds that may contribute to the observed phytotoxicity. However, inhibitory effects observed in solvent controls, particularly with n-hexane and acetone, indicate that solvent-induced phytotoxicity may have influenced the results. Overall, the findings demonstrate the allelopathic potential of C. tuberculata while highlighting the need for further isolation and characterization of its bioactive allelochemicals to clarify the mechanisms underlying its phytotoxic effects.

Keywords: Allelopathy, Caralluma tuberculata, germination, phytotoxicity, phenolic compounds, flavonoids, sandwich method, vegetable crops.