Salicylic Acid Pre-Treatment Reduces the Physiological Damage Caused by the Herbicide Mesosulfuron-methyl + Iodosulfuron-methyl in Wheat (Triticum aestivum)

Chemical herbicides are the most common method of weed control in crops, but they can also negatively affect the host crops, such as wheat (Triticum aestivum L.). The damage caused to the crop plants is often temporary and minor, but sometimes, it can be more substantial, requiring remedial measures. Salicylic acid (SA) is a plant hormone widely used to promote plant growth and to mitigate oxidative stress through its exogenous application. We evaluated the role of exogenously applied SA (as a pre-treatment) in ameliorating the oxidative damage caused by the herbicide mesosulfuron-methyl + iodosulfuron-methyl in wheat plants. The herbicide disrupted the physiological function of plants by affecting several enzymatic antioxidants. The hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents increased at herbicide concentrations higher than 18 g ai ha−1 compared with the untreated control. However, the SA decreased the H2O2 and MDA contents compared with plants that were not treated with SA prior to the herbicide application. The activity of superoxide dismutase (SOD) and polyphenol oxidase (PPO) enzymes increased with increasing rates of the herbicide, as well as over time, regardless of the SA treatment. The activity of catalase (CAT) increased up to the herbicide rate of 18 g ai ha−1 and then decreased at the higher rates, while SA pre-treatment enhanced the CAT activity. The activities of ascorbate peroxidase, peroxidase, and glutathione-S-transferase enzymes generally increased in response to the herbicide application and SA pre-treatment, but fluctuated across different days of sampling following the herbicide application. Herbicide stress also induced high levels of proline production in wheat leaves as compared with the untreated control, while SA pre-treatment decreased the proline contents. Overall, the pre-treatment with different concentrations of SA mitigated the herbicide damage to the physiological functions by regulating the enzymatic antioxidants.