SSR Markers Reveal the Genetic Diversity of Asian Cercis Taxa at the U.S. National Arboretum

Redbud (Cercis spp.) are popular ornamental small trees or shrubs valued commercially for their showy early spring bloom, heart-shaped glossy leaves, and adaptability to diverse environmental conditions. The genus Cercis (Fabaceae) contains 7–13 species or sub-species that occur in North America, Europe, and Asia. There are more than twenty cultivars of eastern redbud (Cercis canadensis) and at least three cultivars of Asian taxa (primarily C. chinensis) in the trade. As part of an ongoing Cercis breeding program, the U.S. National Arboretum has amassed a diverse collection of Cercis germplasm collected in North America and Asia, as well as representative redbud cultivars sold in the United States. Because of their increasing popularity in cultivation in the U.S., we were particularly interested in clarifying the identity and diversity of the Asian Cercis accessions in our collection. We used 16 SSR markers to analyze the genetic diversity of 55 accessions of Asian Cercis taxa from our collection, including C. chinensis, C. gigantea, C. glabra, C. racemosa, and C. yunnanensis. These SSR markers yielded an average of 5.8 alleles per locus (range 2-10), and were used to construct a phenogram using UPGMA clustering. Accessions tended to group by taxa or provenance, but there were some notable exceptions caused either by mis-identification or nomenclatural confusion in the species. This information will be used to improve collection management and decision-making in the breeding program to maximize genetic diversity of cultivated Cercis.