Adaptive and compensatory mechanisms of Imazamox-tolerant sorghum (Sorghum bicolor L.) under combined herbicide and climatic stress

Herbicide-tolerant crops are often regarded as physiologically stable under chemical stress; however, tolerance does not necessarily preclude the activation of adaptive and compensatory mechanisms. The present study aimed to assess the adaptive responses of imazamox-tolerant sorghum (Sorghum bicolor L.) to increasing doses of the herbicide Pulsar 40 (imazamox) by analyzing growth dynamics and key structural elements of productivity. A three-year field experiment was conducted under rainfed conditions in South Central Bulgaria during 2023–2025. Plant height, panicle length, grain mass per panicle, and vegetative biomass were evaluated to identify compensatory responses under herbicide stress. The results revealed that moderate herbicide doses induced temporary growth suppression followed by partial compensatory enhancement of reproductive structures, while excessive doses led to incomplete compensation and reduced productivity. Interannual variability, supported by monthly temperature and rainfall records for April–September, highlighted the role of climatic conditions in modulating adaptive responses. The findings demonstrate that imazamox-tolerant sorghum exhibits dose-dependent adaptive and compensatory mechanisms, emphasizing the importance of optimal herbicide management to support crop resilience and yield stability.