BACKGROUND: Wheat agronomic performance and grain quality vary substantially depending on environmental conditions. However, few studies have evaluated agronomic performance, grain quality stability, and growth stage‐specific climatic regulation together across representative Korean wheat‐production environments. RESULTS: Phenological traits and amylose content showed relatively high stability across multiple environmental conditions, whereas yield components and protein‐related quality traits exhibited pronounced environmental variability. Climatic gradients integrating radiation, temperature, and moisture structured environmental differences and were differentially associated with crop responses across growth stages. Early season climate primarily influenced phenological development, whereas climatic conditions during reproductive growth exerted the strongest control over yield formation and protein‐related traits. An integrated grain quality index further showed that environmental effects were reflected through changes in overall quality performance and differences in interannual stability. CONCLUSION: Variations in wheat performance and grain quality across different environments were governed by structured climatic gradients and developmental timing rather than by isolated site effects. This study provides an analytical framework for distinguishing stable and environment‐sensitive wheat traits by integrating multi‐environment field trials, growth stage‐specific climate gradients, and composite grain quality assessment under Korean agro‐climatic conditions. © 2026 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

This study was conducted to evaluate regional variation in wheat traits within the same genetic background using the Korean-bred cultivar ‘Saekumkang’, thereby minimising genetic effects. Field trials were conducted across six major wheat-growing regions in Korea: Gyeongsangnam-do (GN), Gyeongsangbuk-do (GB), Jeollanam-do (JN), Jeollabuk-do (JB), Chungcheongnam-do (CN), and Chungcheongbuk-do (CB). Regional grain-filling environments were characterised using temperature, vegetation indices, and photosynthesis-related traits measured at approximately 20 days after anthesis. Differences in grain-filling environments and leaf physiological status were accompanied by variation in grain morphology, starch composition, and protein-related traits. Grain area was highest in GN (17.92 ± 0.33 mm²) and lowest in CB (13.41 ± 0.49 mm²). Total grain protein concentration was highest in GB (12.39 ± 3.70 mg/g) and lowest in JN (5.40 ± 1.93 mg/g), whereas total grain starch content was highest in GN (45.09 ± 0.33%) and lowest in CB (36.48 ± 0.22%). Principal component analysis and partial least squares discriminant analysis showed that grain size- and starch-related traits were mainly associated with GN, whereas photosystem II energy flux and protein-related traits were associated with CB or GB. These results indicate that regional grain-filling environments are closely associated with coordinated changes in leaf physiology, grain development, and starch- and protein-related quality traits within a single cultivar, providing baseline information for region-specific wheat quality management.