Morphological, palynological and transcriptomic-based SSR assessment of peony varieties adaptive in the Jiangnan region

The peony shrub belongs to the genus Paeonia in the family Paeoniaceae, is widely used in gardens and has great ornamental and medicinal value. Affected by the local high-temperature and high-humidity climate, there are few peony varieties adapted to growth in Jiangnan, China, and the genetic relationship between the varieties is unclear. In this study, simple repeat sequences (SSRs) were constructed based on transcriptomics, and 20 new SSR molecular markers suitable for peony varieties that adaptive growth in Jiangnan region were developed and characterized. A total of 144 alleles were detected in 38 peony germplasms, the average number of alleles per locus was 6.857, the effective number of alleles ranged from 2.000 to 6.191, and the average was 3.398. The observed heterozygosity (Ho) and expected heterozygosity (He) ranged from 0.056 to 1.000 and 0.258 to 0.855, respectively. Polymorphic information content (PIC) ranged from 0.243 to 0.842 with an average of 0.581, and the Shannon information index (I) ranged from 0.478 to 2.217 and was 1.318 on average. The markers exhibited good polymorphism and generality. The outer wall decoration of pollen grains and the UPGMA clustering method based on the genetic similarity coefficient were used to evaluate the genetic relationship among the peony varieties adapted to the Jiangnan region. The results showed that the results of the cluster analysis using two methods were generally consistent. Most of the native species in Jiangnan were clustered together, and the imported species were clustered together, but some cultivars could not be well distinguished by the differenti-ation morphology of the pollen outer wall, and the UPGMA clustering tree based on SSR molecular markers complemented them. In addition, allele-based population structure analysis further explained the genetic rela-tionship of these varieties. The results of the population structure map showed that extensive gene exchanges occurred among the peony varieties in Jiangnan and the genetic background was more complex; the closer the genetic relationship was, the more similar the genetic composition of the cultivar. The results of this study will provide important auxiliary breeding tools and theoretical guidance for evaluating the genetic diversity, breeding practices, and germplasm innovation of peony varieties in the Jiangnan region.