Allelopathic Effect of Hultholia mimosoides (Lam.) Gagnon & G. P. Lewis and Phytochemical Analysis of Methanol Extract

Abstract

The study evaluated the allelopathic potential of aqueous plant extracts of Hultholia mimosoides, which is an emerging troublesome weed in the plantations of Kerala. The allelopathic effect of the plant was evaluated in laboratory and pot experiments using aqueous leaf extracts. The test crops were rice (Oryza sativa) and cowpea (Vigna unguiculata) and were treated with varied concentrations of 0, 2, 4, 6 and 8 % solution of extract. In the Petri dish study, the aqueous extracts did not significantly affect the germination percentage (above 90% at all concentrations) of both crops.  However, inhibitory effects on root and shoot growth were evident, with inhibition more at higher concentrations and root growth being more sensitive than shoot growth.  In rice, root length decreased from 4.87 cm to 2.81 cm when treated with 8% extract, while in cowpea it reduced from 3.62 cm to 1.25 cm when observations were recorded at seven days after treatment application. Similarly, shoot length declined from 8.12 cm to 6.81 cm in rice and 11.62 cm to 7.37 cm in cowpea seedlings. However, in pot culture with soil media, no significant inhibition of shoot or root growth was observed, indicating the absence of allelopathic effect under natural conditions due to losses from soil or bio-degradation of active principles due to microbial action. The study also aimed to identify the biochemicals present in the plant using GC-MS analysis of methanolic extract. The major compound identified was 1,2,3-benzenetriol (pyrogallol), accounting for 46.29% of the total chromatogram area, which is a gallic acid derivative that possesses allelopathic property. The chromatographic analysis revealed the presence of several other bioactive compounds, including phenolic compounds, esters, and fatty acid derivatives. Many of these compounds have been reported to possess antioxidant, antimicrobial, and allelopathic activities.