Comprehensive Evaluation of Root Morphological Indices of 204 Gossypium hirsutum Germplasm in Seedling Stage

The root phenotype of cotton seedlings serves as a criterion for selecting high-vigour varieties, yet systematic evaluations of Upland Cotton germplasm resources remain limited. We measured nine root- and shoot-related traits in 204 Gossypium hirsutum accessions from diverse ecological regions. Correlation analysis revealed that root surface area, volume, and fresh weight were closely interrelated indicators. Principal component analysis extracted two biologically meaningful factors—‘absorptive capacity’ and ‘morphological strategy’—with a cumulative contribution of 55.72%. Cluster analysis classified the accessions into three functional groups: high-yield potential (n = 15), balanced adaptation (n = 135), and fine-root dominance (n = 54). These clusters corresponded with ecological origins and breeding periods, reflecting local adaptation. We propose root surface area, volume, and fresh weight as cost-effective screening indicators and identified 15 elite accessions as potential parents for root-centred breeding. These findings are particularly relevant for the arid production environments of Northwestern China.