Allelopathic and phytotoxic effects of hexanic extract of leaves and flowers of Sinapis arvensis on Triticum aestivum: chemical composition and bioactivity

Abstract

The need to develop agricultural practices has intensified the search for natural alternatives to synthetic agrochemicals, with the aim of reducing the risks of these synthetic chemical compounds. This study compared the allelopathic and phytotoxic effects of Sinapis arvensis hexanic extract of leaves and flowers on the germination and early growth of Triticum aestivum . These biological activities were evaluated in relation to the chemical profiles, α-amylase inhibitory activities, as well as the antioxidant and antimicrobial properties of the extracts. The phytochemical profiles of the two extracts were established by gas chromatography–mass spectrometry (GC–MS) and tested for antioxidant, antimicrobial, and enzymatic inhibitory properties. The experiment followed a completely randomized design with three independent replicates per treatment. For each extract type (leaf or flower) and concentration (0, 0.625, 1.25, 2.5, and 5 mg/mL), three replicate Petri dishes containing 100 seeds each were used for every treatment combination. Control seeds received distilled water with 5% Tween-20 as a vehicle control. leaf hexane extract was composed mainly of trans-geranylgeraniol, isocitronellol, and fatty acid methyl esters, while flower hexane extract contained abundant sesquiterpenes such as cubenol, cedrol, and caryophyllene. Both hexanic extract of leaves and flowers exerted concentration-dependent inhibitory effects on seed germination, radicle and hypocotyl elongation, and seedling biomass, with the leaf hexane extract being remarkably more potent. The highest concentration (5 mg/ml) of leaf and flower extracts significantly reduced seed germination as well as radicle and hypocotyl growth (length and weight) compared to the control group. Notably, the extracts significantly decreased α-amylase activity in a dose-dependent manner. Moreover, both extracts showed moderate antioxidant activity with the flowers being more effective in radicals’ scavenging and exhibited antimicrobial effects mainly against Gram-positive bacteria. Overall, these findings demonstrate that S. arvensis is a rich source of bioactive secondary metabolites with potent allelopathic potential. The observed phytotoxic, antioxidant, and antimicrobial effects provide a mechanistic basis for understanding this allelopathic activity and its potential role in plant–plant interference.