Hormetic responses of niger (Guizotia abyssinica Cass.) to imazethapyr under field conditions

This field experiment, conducted in 2023, assessed the effects of ten imazethapyr dosages (0, 0.375, 0.75, 1.5, 3, 6, 12, 25, 50, and 100 g a.i. ha⁻¹) on the activities of the antioxidant enzymes catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX), as well as on growth and grain yield of niger plants. No visible phytotoxicity was detected at 0.375-0.75 g a.i. ha⁻¹, whereas leaf scorch increased markedly at 1.5 g a.i. ha⁻¹ and higher. Some recovery was observed at dosages of 1.5 to 12 g a.i. ha⁻¹ while chlorosis at dosages of 25 to 100 became progressively more severe over time. Overall, high imazethapyr concentrations reduced photosynthetic pigments and growth parameters, while antioxidant enzyme activities showed dose-dependent increases. High herbicide concentrations reduced grain yield and elevated malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and proline levels, whereas lower concentrations produced the opposite pattern of response. Chlorophyll exhibited greater sensitivity to imazethapyr than carotenoids. Among the antioxidant enzymes, GPX showed the greatest dose‑responsive change to imazethapyr application. The results of this experiment indicated a hormetic response of imazethapyr on niger plants, as reactive oxygen species (ROS) production and consequently membrane lipid peroxidation were decreased while grain yield was increased at low herbicide concentrations. Moreover, the activity of CAT, compared to those of APX and GPX showed a stronger correlation with the hormetic effects of imazethapyr. These findings suggest that applying imazethapyr at lower concentrations may improve crop performance under specific conditions and support more efficient and sustainable management practices.