| Summary: | Cold stress significantly impacts sesame during its early growth stages, with varying responses observed among different genotypes. Ten genotypes were evaluated for phenotypic response to various temperatures during germination. Cold stress at 10, 12, 14, and 16 °C inhibited germination, with zero germination at 10 °C. At 14 °C, genotypes showed significant germination variation, and it was selected as the threshold temperature for assessing cold tolerance in sesame. Four genotypes were grouped into two, and each group with extreme germination responses (high and low) were selected for further biochemical and physiological studies. Genotypes V5 and V7 exhibited higher cold tolerance, better germination percentage, and seedling parameters under low temperatures, while V8 and V9 showed significant reductions, indicating cold sensitivity. Biochemical analyses revealed that cold-tolerant genotypes had enhanced activities of antioxidant enzymes, including catalase, superoxide dismutase, and peroxidase, as well as higher proline accumulation compared to sensitive genotypes. These antioxidants played a crucial role in mitigating the oxidative stress induced by cold, as evidenced by lower levels of hydrogen peroxide and malondialdehyde in the tolerant genotypes. Cold-tolerant genotypes also accumulated higher soluble sugars and protein levels, contributing to osmotic regulation and membrane stability. The findings highlight the importance of enzymatic and non-enzymatic antioxidants in cold stress tolerance, suggesting these biochemical markers could be used to identify and develop cold-resistant sesame cultivars. The results offer valuable insights into the mechanisms underlying cold tolerance and provide a foundation for breeding efforts to improve sesame cold resistance.
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