Field assessment of physiological and yield responses of potato to glyphosate hormesis

Hormetic effects refer to the phenomenon in which lowdoses of certain herbicides, such as glyphosate, stimulate plant growth rather than inhibit it. A field experiment was conducted using six glyphosate application rates (5, 10, 20, 40, 80, and 160 g a.e. ha^-1), along with an untreated control on potato plants. The activity of enzymatic antioxidants, including catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX), as well as levels of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and leaf protein content, were evaluated, along with plant height, tuber yield, and tuber size distribution. The highest yield was recorded at a low glyphosate dose of (20 g a.e. ha^-1), where tuber production increased by approximately 30% compared to the control. This treatment also resulted in a 54% increase in marketable tubers (> 150 g) and a 14% increase in total biomass. In contrast, the highest glyphosate rate (160 g a.e. ha^-1) significantly reduced total yield, marketable tubers, total biomass, and plant height. This treatment also led to the highest levels of APX and GPX activity, along with elevated concentrations of MDA and H₂O₂. However, the highest CAT enzyme activity was observed at 20 g a.e. ha^-1 glyphosate rate. These findings suggest that low-dose glyphosate applications, up to 20 g a.e. ha^-1, can enhance potato yield; however, rates exceeding this threshold may negatively affect yield.