Azadirachta indica leaf methanol extract inhibits acetolactate synthase, thioesterase and antioxidant enzymes in Euphorbia heterophylla and Chromolena odorata weeds

Synthetic herbicides generate resistance in weeds and cause environmental toxicity affecting other organisms in the ecosystem. Azadirachta indica (Neem) contains diverse phytochemicals with reported pharmacological and allelopathic potentials which could be employed in controlling growth of weeds. This study examined the bioherbicidal potential of A. indica against Euphorbia heterophylla, and Chromolena odorata. Fresh leaves of A. indica were collected, air-dried and ground into fine powder. The powdered sample was subjected to methanol Soxhlet extraction to obtain Azadirachta indica leaf methanol extract (AILME), followed by rotary evaporation and oven-drying to obtain dry AILME. Fresh leaves of Euphorbia heterophylla and Chromolena odorata weeds were collected, washed, and macerated (10 g in 30 ml phosphate buffer) and used for biochemical assays. The AIMLE was analyzed using High-performance liquid chromatography (HPLC) and Gas Chromatography-Flame Ionization Detection (GC-FID). In-vitro effects of the extract were tested on the activities of acetolactate synthase (ALS), thioesterase, superoxide dismutase (SOD), catalase and glutathione transferase (GST) in E. heterophylla and C. odorata. The HPLC identified B-Caryophyllene, Trans-B-Farnes, Alpha Ionone, Quercetin and Azadirachtol, while GC-FID showed Azadirachtol and Azadirachnol as major compounds in AIMLE. The AILME reduced ALS and thioesterase activities comparable to the standards, glufosinate and glyphosate in Euphorbiaheterophylla. The AILME reduced SOD and GST activities in C. odorata weed comparable to standards. This study thus indicates that A. indica leaf extract contains phytochemicals, exerting herbicidal potential involving oxidative stress and disruptions of amino acid and fatty acid biosynthesis in E. heterophylla and C. odorata.