Balancing of Oxidative Stress and Antioxidant Accumulation in Finger Millet under High Temperature and Elevated CO₂ × Drought Stress Interactions

Abstract

Aims: The study aimed to evaluate the oxidative stress responses and antioxidant regulation in four finger millet genotypes (GPU 28, ML 365, GPU 66, and GPU 67) under high temperature and elevated CO₂ x drought stress interaction. Study Design: A controlled pot experiment was conducted with two-factorial Completely Randomized Design (CRD) to assess oxidative stress indicators and antioxidant activity under varied environmental stress combinations. Place and Duration of Study: The experiment was carried out at the College of Agriculture, Vellayani, using Polyhouse and Open Top Chamber (OTC) facilities during the 2023–2025 cropping seasons. Methodology: Four finger millet genotypes were exposed to high temperature and elevated CO₂ with drought treatments. Hydrogen peroxide (H₂O₂) accumulation in leaves was detected by 3,3′-diaminobenzidine (DAB) staining to visualize oxidative damage, while total antioxidant activity was estimated using the ferric reducing antioxidant power (FRAP) assay. The intensity of DAB staining and FRAP values were compared among genotypes and treatments to assess stress-induced variations in reactive oxygen species (ROS) accumulation and antioxidant defence. Results: High temperature stress caused intense DAB staining in all genotypes, indicating severe oxidative stress, with GPU 67 showing the highest H₂O₂ accumulation and GPU 28 the lowest. Under elevated CO₂ x drought interaction, lighter staining patterns were observed, suggesting reduced ROS buildup due to CO₂-induced mitigation of oxidative injury. Antioxidant activity increased significantly under both stress conditions, with the maximum increase recorded in ML 365 (5 fold) and GPU 28 (4 fold) under heat stress. Elevated CO₂ and drought also enhanced antioxidant levels, though to a lesser degree. Conclusion: High temperature imposed the greatest oxidative load on finger millet, while elevated CO₂ alleviated stress effects. Efficient antioxidant regulation indicates their potential resilience and productivity under future climate change scenarios. These findings provide valuable insights for breeding heat- and drought-resilient finger millet genotypes under future climate change scenarios.