Root system architecture responses to high-temperature stress in synthetic-derived wheat lines reveal distinct adaptive patterns

High-temperature stress poses a major threat to wheat productivity, particularly during early developmental stages. Root system architecture (RSA) plays a key role in stress adaptation; however, its variation under high-temperature stress remains insufficiently characterized, especially in genetically diverse populations. In this study, we evaluated RSA responses of representative genotypes from a Multiple Synthetic Derivatives (MSD) wheat population under control and high-temperature conditions using a time-resolved two-dimensional phenotyping platform. High-temperature stress significantly affected most root traits, with lateral root-related parameters, including second pair seminal root length (SPSRL), root system width (RSW), and convex hull area (CHA), showing relatively greater responsiveness than vertical traits. Integrative analyses combining stress indices and multivariate approaches revealed distinct genotypic response patterns. MSD417 and MSD034 maintained higher root performance under stress, indicating greater tolerance, whereas MSD392 exhibited pronounced sensitivity, and MSD054 showed limited responsiveness. These findings suggest the importance of distinguishing between active stress tolerance and apparent stability and indicate that lateral root-related traits may represent useful targets for selection. Overall, the findings of this study validate the practical usefulness of the RSA screening approach and identify MSD genetic resources harboring RSA traits relevant to breeding heat-resilient wheat.