Haplotype‐based insights into seminal root angle in barley

Root system architecture (RSA) plays a crucial role in crop adaptation and yield stability, especially in the context of climate change and variable growing conditions. Despite this, the genetic basis of RSA remains poorly understood in barley (Hordeum vulgare L.), necessitating the need for more research to better characterize this architecture and explore the potential of diverse germplasm for trait improvement. In this study, we aimed to dissect the genetic basis of seminal root angle (SRA) by examining natural variation within a diverse global collection of 816 barley accessions, including both landraces and modern cultivars. Using a haplotype-based mapping approach, which reflects the recombination patterns considered in breeding programs, we identified chromosomal regions associated with SRA variation. Notably, two major genomic regions on chromosome 5H were identified as novel, while a previously reported region, RAQ1, was confirmed on chromosome 3H. Our analysis revealed significant genetic diversity for SRA within the global collection, with accessions from distinct geographic origins exhibiting unique haplotype combinations. This finding underscores the quantitative nature of the SRA trait and suggests the likelihood of inadvertent selection through polygenic traits related to canopy or yield in commercial breeding programs. To further explore the genetic potential of SRA, we employed a simulation approach to evaluate the feasibility of creating an "ultimate genotype" for narrow SRA. Our results highlight the challenges associated with significantly altering SRA through traditional breeding approaches due to its quantitative, polygenic nature. Consequently, we recommend the integration of predictive and precision breeding techniques, such as genomic selection and gene editing, to effectively capture genetic diversity and accelerate RSA improvement in barley.