Genetic diversity generated by introgression between wild species and cultivars of tree peony in Baokang, China

Tree peonies distributed in Baokang County (Hubei Province, China) (BKTPs) displayed extensive morphological variation, especially in flower color patterns and fruit setting rates. The genetic diversity of BKTPs and their relationships to nine wild species and 14 representative traditional cultivars were assessed using simple sequence repeat (SSR) markers in this study. All 19 analyzed loci were polymorphic, and 85 alleles were found. The number of alleles per locus varied from 3 to 7, with an average of 4.474. Cluster analysis with UPGMA method based on SSR markers partitioned 46 accessions of BKTPs into two major clusters and six subgroups, closing to P. ostii, P. qiui, P. rockii, P. jishanensis and different cultivars, respectively. Analysis of flavonoids with UPLC-Q-TOF-MS/MS revealed that Pn3G5G and Cy3G5G were the main anthocyanins of the pink and reddish-purple flowers of BKTPs, which were undetectable in white flowers. The fruit and seed setting rates of BKTPs ranged from 4.00 to 26.00 per plant, and 130.00 to 858.00 per plant, respectively. The content of unsaturated fatty acids was over 90% of the total fatty acids in the seed oils of BKTPs, with α-linolenic acid as the dominant compound (42.51–54.93%). Both phenotypic and molecular data suggested that the accessions of BKTPs were a hybrid complex resulted from introgression between the sympatrically distributed wild species and cultivars in Baokang, which provided novel genetic resources for tree peony breeding and germplasm innovation.