Heat stress is a major abiotic constraint that increasingly threatens plant survival, growth, and productivity under changing climatic conditions. Like many crops, chilli is also highly sensitive to heat stress. This study was planned to understand the biochemical response, identify the critical growth phase and physio-reproductive parameters of chilli genotypes under heat stress. The present study elucidates heat stress mediated alterations in lipid peroxidation and antioxidant defense mechanisms in chilli genotypes during dual phases of plant growth I.e. vegetative and reproductive stages. Twenty-two chilli genotypes were exposed to conditions of ambient temperature (Control/AT; 30–35 °C) and Heat stress (HT; 36–42 °C) regimes to evaluate oxidative stress responses and adaptive defense strategies. Key biochemical indicators, including proline accumulation, hydrogen peroxide (H₂O₂), malondialdehyde (MDA) content, and activities of major antioxidant enzymes, were quantified to assess reactive oxygen species (ROS) scavenging efficiency. Among the evaluated genotypes, A-17-10, A-17-2, and A-5-4 exhibited markedly higher proline accumulation under heat stress. Lipid peroxidation, as indicated by MDA content, was highest in LCA-424 (32.95µmol/gFw) and lowest in A-17-10 (26.34µmol/gFw), highlighting substantial genotypic variability in membrane stability. Hydrogen peroxide levels across both growth stages peaked in Anugraha (2.21 μmol g⁻1 FW), indicating its sensitivity to heat stress. Antioxidant enzyme profiling revealed maximum peroxidase activity in A-17-2 and minimum activity in Swati Palampur. Superoxide dismutase (SOD) activity during the vegetative stage was highest in A-17-10 and lowest in Swati Palampur, while catalase activity ranged from 14 Unit activity/gFw in A-17-2 to 10.08 Unit activity/gFw in Pusa Sadabahar. Heat stress had a greater impact at the reproductive stage, as shown by higher catalase, SOD, and peroxidase activities. The strong antioxidant response in A-17-2 and A-17-10 indicates inherent, stage-specific mechanisms that limit oxidative damage under high temperatures. Factorial analysis grouped genotypes into four clusters, revealing distinct adaptive responses to heat stress. The study identifies key antioxidant traits and elite genotypes that can be utilized for developing climate-resilient chilli cultivars to sustain productivity under rising temperatures. Future research focusing on molecular mechanisms in chilli will further elucidate cellular responses to heat stress and support advanced breeding strategies.
P.V. et al. (Fri,) studied this question.