Physiological response of imazamox-tolerant sorghum (Sorghum bicolor L.) to increasing doses of imazamox under field conditions

Herbicide-tolerant sorghum hybrids provide expanded opportunities for chemical weed control; however, herbicide tolerance does not necessarily imply the absence of physiological stress. The present study aimed to evaluate the physiological response of the imazamox-tolerant sorghum hybrid Sentinel IG to increasing doses of the herbicide Pulsar 40 (active ingredient: imazamox). A field experiment was conducted under rainfed conditions during the 2024 growing season in South Central Bulgaria. Net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), and chlorophyll concentration were measured at two time points after herbicide application. In addition, plant height was recorded at key developmental stages. The results demonstrated a clear dose-dependent reduction in chlorophyll concentration, photosynthetic activity, and transpiration intensity with increasing herbicide dose. Although partial recovery of physiological parameters was observed over time, the highest dose (480 ml da⁻¹) resulted in sustained physiological stress and growth suppression. The findings confirm that even herbicide-tolerant sorghum hybrids exhibit measurable physiological responses when exposed to elevated doses of imazamox, highlighting the importance of dose optimization to ensure crop safety under field conditions.