Salt Tolerance Variation among Chenopodium quinoa Accessions of Contrasting Geographic Origins: Germination Performance and Antioxidant Defense under NaCl Stress.

<b>Background and Objective:</b> Chenopodium quinoa Willd. is a strategic crop for food security in salt-affected regions; however, genotype-specific physiological responses to salinity during early germination remain insufficiently characterized. Understanding variation among geographically distinct accessions is essential for identifying salt-tolerant genotypes. This study aimed to evaluate germination performance and antioxidant defense responses of three quinoa accessions of contrasting geographic origins under salinity stress. <b>Materials and Methods:</b> Three quinoa accessions 18GR (Ames 13724, USA), R-132 (PI 478418, Bolivia) and DE-1 (PI 674266, Ecuador) obtained from the USDA National Plant Germplasm System were evaluated under four NaCl concentrations (0, 100, 200 and 300 mM) under controlled laboratory conditions. Germination percentage, mean germination time (MGT), radicle length and germination kinetics were recorded. Reversibility assays were conducted to differentiate osmotic and ionic effects of salinity. Oxidative stress markers, including Hydrogen Peroxide (H<sub>2</sub>O<sub>2</sub>) and malondialdehyde (MDA), were quantified along with antioxidant enzyme activities such as peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX). Proline accumulation was also assessed as an indicator of osmotic adjustment. <b>Results:</b> Salinity significantly affected germination traits in an accession-dependent manner. At 300 mM NaCl, germination rates were 90, 60 and 33.33% for 18GR, R-132 and DE-1, respectively. Reversibility assays indicated osmotic stress predominance at 200 mM, while ionic toxicity dominated at higher concentrations. NaCl stress increased H<sub>2</sub>O<sub>2</sub> and MDA accumulation in all accessions. POD activity increased consistently across treatments. CAT and APX activities in 18GR showed a biphasic response, being stimulated up to 200 mM and inhibited at 300 mM, indicating stress threshold regulation. Proline accumulation increased with salinity, with 18GR showing the highest osmotic adjustment capacity. <b>Conclusion:</b> Geographic origin significantly influences salt tolerance during germination in quinoa. Accession 18GR exhibited superior stress tolerance and antioxidant regulation, making it a promising candidate for saline agriculture. The contrasting biochemical responses provide a physiological basis for selecting salt-tolerant quinoa genotypes adapted to arid and semi-arid environments.