Biological and eco-friendly control agents have recently gained more attention due to environmental pollution and weed species' resistance to synthetic herbicides. As allelochemicals, essential oils (EOs) and terpenoid volatile compounds have been considered suitable alternatives to develop environmentally friendly herbicides. This work aimed to evaluate the phytotoxic activity of Artemisia austriaca Jacq. essential oil (AAEO), and its major constituents, i.e. the oxygenated monoterpenes camphor and 1,8-cineole, on seed germination and seedling growth of the weed Avena fatua L. The AAEO was rich in oxygenated monoterpenes, mostly comprising of camphor (21.62 %), 1,8-cineole (13.45 %), beta-myrcene (7.77 %), and borneol (7.06 %). The AAEO, 1,8-cineole, and camphor completely suppressed the seed germination of A. fatua at 200 ppm and reduced seedling growth. Simultaneously, the photosynthetic pigments and total soluble protein content of seedlings were also decreased (up to 99.52 and 60.26 %, respectively). Phenols and flavonoids were increased up to 3.93-fold at low concentrations, while their content decreased after exposure to high concentrations of terpenoids. The enzymatic antioxidant defense system reacted variably to the volatile compounds. CAT and POD activities decreased at high concentrations up to 75.82 %, while they increased at low concentrations up to 2.79-fold. The content of H2O2, 2 O 2 , O 2 , OH, , MDA, and REL highly enhanced in A. fatua seedlings when treated with AAEO, 1,8-cineole, and camphor up to 13.58-fold, 75.06 %, 22.66-fold, 2.31-fold and 3.58-fold, respectively. Overall, the present results revealed that AAEO and its major constituents possess noteworthy phytotoxic activity on A. fatua by inducing oxidative stress and reducing cell viability. Therefore, they can be considered as valid candidates to develop natural herbicides in sustainable agriculture.
