Allelopathic Potential of the Aromatic Plants Cymbopogon nardus and Lantana camara Against Distinct Malaysian Weedy Rice Biotypes (Early view)

Abstract

Weedy rice (Oryza sativa complex) remains one of the major constraints in Malaysian rice production, as continuous herbicide dependence has intensified resistance issues and increased environmental concerns. This study evaluated the allelopathic potential of two aromatic plants, Cymbopogon nardus and Lantana camara, against two weedy rice variants (WRN and WRE) and the cultivated MR220 CL2 variety. Volatilisation, foliage leachate and plant-box root exudation assays were conducted to determine their inhibitory effects under different exposure pathways. C. nardus consistently produced stronger and more selective inhibition than L. camara, with the greatest reduction in radicle elongation recorded in WRN and WRE at shorter distances from the donor plant. Regression analysis further demonstrated a distance-dependent inhibitory pattern, particularly in the weedy rice variants, whereas MR220 CL2 showed comparatively lower sensitivity. GC–MS analysis revealed that the methanolic extract of C. nardus was dominated by volatile monoterpenes, including geraniol, citral, citronellol, caryophyllene and geranyl acetate, while the aqueous extract contained mainly semivolatile fatty acid methyl esters such as methyl palmitate, methyl stearate and 9,12-octadecadienoic acid methyl ester. The contrasting chemical profiles suggest that C. nardus expresses both volatile- and water-mediated allelopathic activity through multiple classes of secondary metabolites. Overall, the stronger inhibitory effects observed against the weedy rice variants indicate that C. nardus may serve as a promising allelopathic donor species for future studies on sustainable weed management in rice production systems.