Humic Acid and Selenium Supplementation Modulate the Growth and Antioxidant Potential of Chili under Cadmium Stress

Maximizing food production under adverse conditions is a major challenge to food security and sustainability in the face of population growth and climatic change. The use of amendments applied as a supplement under adverse conditions may play a significant role in the mitigation of biotic and abiotic stress. This study aimed to explore the morpho-physio-biochemical changes in chili in response to cadmium (Cd) stress. The present study investigated the effects of foliar-applied selenium (Na₂SeO₄) (3 µM) and soil-applied humic acid (250 mg kg⁻¹ <i>w</i>/<i>w</i> soil) in the sole and synergistic form under varying levels of cadmium stress (0, 2, and 4 mM using CdCl₂) in chili. Results revealed that a linear decrease was noticed in the growth, biomass, and phenological attributes of chili plants by increasing the Cd stress. More reduction was noticed at the higher levels of Cd stress as compared to control due lowering plant dry weight (18.15 and 39.67%), relative water content (RWC) (10.73 and 24.17%), total chlorophyll concentrations (16.01 and 31.44%) and increased electrolyte leakage (49.44 and 129.35%) and malonaldehyde contents (MDA) (68.41 and 104.04%). Dry biomass significantly increased with humic acid and selenium treatments, regardless of cadmium level. The reduced enzymatic activities associated with reactive oxygen species (ROS) detoxification, underscores the pivotal role of Se and humic acid in maintaining redox homeostasis. The combined effect of selenium and humic acid proved better results as compared to the sole application in minimizing Cd uptake in roots and fruit. This study demonstrates that the application of humic acid and selenium activates physio-biochemical defense responses against cadmium stress in chili plants and provides significant pavement for the cultivation of chili in cadmium-containing soils with a target of high-yielding and quality.