Quinoa (Chenopodium quinoa Willd.) is a newly emerging crop of the world, but is sensitive to episodes of heat stress especially at terminal growth stage. Therefore, strategies need to be adopted for improving terminal heat stress tolerance in quinoa. In this study, an elite quinoa genotype (UAF Q7) was grown to examine the effect of terminal heat stress in terms of physiological attributes and seed yield and quality attributes and their possible improvement with the foliar spray of water and optimized levels of moringa fresh leaf extract (MLE, 3%), Sorgaab (3%), hydrogen peroxide (H2O2, 100 mu M) and ascorbic acid (AsA, 500 mu M). Analysis of leaves in close proximity to the inflorescence revealed that heat stress reduced the chlorophyll (Chl) a, b and carotenoids. Heat stress also inhibited the net rate of photosynthesis (Pn), transpiration rate (E), and stomatal conductance (gs) as a function of closure of stomata and increased the sub-stomatal CO(2 )concentration (Ci) as a function of reduced ability of mesophyll parenchyma to assimilate CO2 present intercellular. The foliar spray of MLE, Sorgaab, H2O2 and AsA was promising in averting (up to 55-70%) the terminal heat stress induced changes on the photosynthetic pigments and gas exchange attributes. A prominent increase in the concentration of leaf H2O2 and malondialdehyde (MDA) due to heat stress was markedly declined with the foliar spray of the abovementioned foliar spray agents. The activity of antioxidants including catalase, peroxidase and dismutase was improved with all foliar spray treatments but was the highest with MLE and Sorgaab. Heat stress induced deterioration in the seed yield and seed nutritional quality was substantially improved with all the foliar spray treatments but more distinctly with MLA and Sorgaab and lesser with water. In crux, terminal heat stress induced reductions in physiological, seed yield and seed nutritional quality of quinoa can be successfully recuperated with foliar spray especially of MLE and Sorgaab. (C) 2020 Friends Science Publishers
