Effective phytotoxicity of Rhazya stricta essential oils on the weeds Dactyloctenium aegyptiumand Chenopodiastrum murale

AbstractEssential oil (EO) allelopathy has been considered as potential applications in organic agriculture and weed management, where the EOs can be used as eco-friendly natural herbicides. Rhazya strictais a widely distributed dwarf shrub in the Arabian Peninsula and is characterized by its toxicity. The present study aimed to investigate the chemical composition of the R. strictaEO using quantitative and qualitative analysis via Gas chromatography/ mass spectroscopy (GC-MS) and GC-flame ionization detection (GC-FID) as well as assess its phytotoxicity on weeds. Fifty-four volatile components were identified, representing 97.5% of total oil. The terpenes were found as the backbone of the oil constituents including mono- (55.28%) and sesqui-terpenes (27.35%), alongside non-terpenoid constituents (13.63%). From the overall identified oil constituents, trans-chrysanthenyl acetate (31.57%), cis-verbenol (11.84%), octadecenoic acid, methyl ester (4.84%), cubenol (4.82%), davana ether (4.79%), (E)-9-octadecenoic acid ethyl ester (3.93%) represented the abundant compounds. The EO exhibited strong phytotoxicity on the germination and seedling growth of weeds Dactyloctenium aegyptiumand Chenopodiastrum muralecompared to the crop Triticum aestivum. The EO showed an IC50of 6.66, 7.75, and 6.45 mg/L for seed germination, shoot growth, and root growth, respectively for the weed D. aegyptium, while it showed 5.41, 8.33, and 6.82 mg/L for C. muralecompared to 16.9, 18.5, and 19.5 for T. aestivummg/L for seed germination, shoot growth, and root growth, respectively. The observed strong phytotoxicity could be ascribed to the higher content of the oxygenated terpenoid compounds, whereas, further study is recommended to evaluate the phytotoxicity of the major compounds either singularly or in combination against weeds and determine their mode(s) of action as bioherbicides.