Phenotypic Diversity, Oil Quality Evaluation, and Elite Germplasm Screening of Xanthoceras sorbifolium Germplasm Resources

To enrich the breeding resources of Xanthoceras sorbifolium and provide support for its industrialization, we conducted multi-trait comparisons and comprehensive evaluations of 48 elite X. sorbifolium clones with high oil contents and high comprehensive utilization values, based on germplasms preserved at Qiuxian Forest Farm, Handan, Hebei Province, China. The coefficients of variation for quantitative traits were 7.04–74.16%, with variability being greatest in shell and fruit weights. Cluster analysis categorized the 48 germplasms into four distinct groups, with marked inter-group trait differences. Soluble protein, soluble sugar, and starch contents varied significantly among accessions. The average kernel oil content was 60.30%, differences in oil content were validated at the cellular level through microscopic oil body observations. Correlation analysis demonstrated that comprehensive oil content was strongly significantly positively correlated with fruit- and seed-related traits, whereas oil content was strongly significantly negatively correlated with fruit shell thickness and seed coat thickness. Principal component analysis extracted five principal components with a cumulative contribution rate of 72.747%, encapsulating four core information dimensions: fruit and seed size, oil content, protein quality, and energy substances. Membership function analysis, selected germplasms G10, G2, G4, G7, G20, G24, G17, G, G34, and G5 as optimal accessions. These clones are suitable core breeding materials due to their outstanding performance in terms of nutrient content, geometric characteristics, and fruit and seed weights. Notably, G24, G5, and G17 demonstrated significant advantages in oil quality with high linoleic acid (C18:2), oleic acid (C18:1), and nervonic acid (C24:1) contents, respectively, indicating the excellent potential of X. sorbifolium development for oil production.