University of Tabriz Journal of Plant Physiology and Breeding 2008-5168 16 2 2026 05 01 Physiological responses associated with improved yield performance under heat stress in proso millet: the role of rice bran-coated urea in re-programming growth and partitioning 1 20 21330 10.22034/jppb.2026.70781.1404 EN Sirous Hassannejad Department of Plant Eco-Physiology, University of Tabriz, Tabriz, Iran. Shurooq Abbas Department of Plant Eco-Physiology, University of Tabriz, Tabriz, Iran. Soheila Porheidar Ghafarbi Dryland Agricultural Research Institute, Agricultural Research, Education, and Extension Organization (AREEO), Maragheh, Iran. 0000-0003-0789-2534 Journal Article 2025 12 18 <strong>Objective: </strong>Heat stress disrupts the photosynthetic machinery and shortens developmental phases, leading to yield loss in cereals. This study investigated the potential of rice bran-coated urea (RBCU) to ameliorate heat-induced constraints on growth, phenology, and dry matter partitioning in proso millet (<em>Panicum miliaceum</em> L.).<br /><strong>Methods:</strong> A two-year field experiment evaluated uncoated urea (UCU), RBCU, gypsum-coated urea (GCU), and cement-coated urea (CCU) at four nitrogen rates (0, 60, 80, and 120 kg urea ha^-¹) under optimal (spring) and heat stress (summer) conditions. The experiment was conducted as a split-plot factorial arrangment based on a randomized complete block design with three replications. The main plots included planting season (spring and summer seasons), while the subplots consisted of the factorial combination of coating type and urea-N rate. In this study, several traits, including days to heading, days to physiological maturity, chlorophyll a, total carotenoids, leaf area, panicle length, biomass, grain yield, and harvest index,<em> </em>were measured.<br /><strong>Results: </strong>The<strong> </strong>results indicated that RBCU at 80 kg urea ha^-¹ generally ranked among the best-performing treatments, particularly under summer conditions. Under summer heat stress, RBCU maintained significantly higher chlorophyll a and carotenoid contents, increasing chlorophyll <em>a</em> and carotenoids by 25.4% and nearly twofold, respectively, compared with the stressed UCU control. It concurrently improved canopy architecture, increasing leaf area and panicle length by 14.9% and 15.2%, respectively. RBCU also modulated crop phenology by delaying heading by 11.5%, and was associated with an improved dry matter partitioning efficiency, reflected in a higher harvest index. It increased total biomass by 17.3% and, most importantly, enhanced the harvest index by 6.3% under severe stress, indicating a more efficient allocation of assimilates to grains. Consequently, grain yield with RBCU at 80 kg urea ha^-¹ was 17.5% higher than that with UCU under summer conditions.<br /><strong>Conclusion: </strong>RBCU was associated with improved physiological performance and higher yield under summer heat conditions, likely through coordinated effects on canopy traits, phenology, and harvest index. https://breeding.tabrizu.ac.ir/article_21330_faabf5173c6ae93e0c635ffbbbb593be.pdf