Phenotypic and Genetic Diversity of Hydrangea Germplasm Resources and the Construction of DNA Fingerprint Profiles

This study assessed the genetic diversity of 30 Hydrangea accessions (21 wild species and 9 cultivated varieties) using 33 morphological traits and 22 pairs of polymorphic SSR markers. Morphological analysis showed that for 24 qualitative traits, the Shannon–Wiener index (H′) ranged from 0.124 to 1.559, the Simpson index (D) ranged from 0.260 to 0.816, and the Pielou evenness index (E) ranged from 0.179 to 0.948; for the 9 quantitative traits, H′ ranged from 0.534 to 1.267, E ranged from 0.486 to 0.972, and the coefficient of variation ranged from 11.53% to 70.76%, This indicates that phenotypic variation in quantitative traits is rich and evenly distributed. Principal component analysis identified 9 principal components with a cumulative contribution of 76.998%; comprehensive membership function evaluation was used to screen for germplasm with excellent overall traits, such as H.m. ‘Hua kai fu gui’, H.m.‘Bo da lan’, and H.m. ‘Jin se shi yun’. SSR analysis amplified a total of 30 alleles, with the number of effective alleles (Ne) ranging from 3.838 to 23.041, the Shannon diversity index (I) ranging from 1.647 to 3.362, and the polymorphism information content (PIC) ranging from 0.710 to 0.979 (mean 0.894). The Mantel test revealed no significant correlation between morphological and molecular data (r = 0.003, p = 0.517), indicating that the two types of data provide complementary information. Cluster analysis based on morphological traits and SSR markers classified the tested germplasm into 4 and 2 clusters, respectively, both of which effectively distinguished wild species from cultivated varieties; the PCA results were consistent with the clustering results. As few as three pairs of SSR markers were sufficient to distinguish all 30 accessions; using eight pairs of core primers, DNA fingerprint profiles and corresponding QR codes were successfully constructed for each accession. The results indicate that combining morphological traits with SSR markers is an effective approach for the identification, conservation, and breeding utilization of Hydrangea germplasm resources.