Genetics and Genomics of Cornus florida and C. kousa to Enhance Dogwood Breeding

Flowering dogwoods (Cornus florida L.) and kousa dogwoods (C. kousa F. Buerger ex Hance) are extensively planted in the United States (U.S.) as ornamental trees for their showy display in the spring and overall year-round appeal. In 2019, dogwoods collectively ranked third in value for deciduous flowering trees in the U.S. and generated more than $31 million in wholesale and retail sales. Tennessee leads the country in the number of dogwood plants sold, selling almost double the number of trees as the next producing state in the country. The showy bracts of both dogwoods are modified leaves with a spectrum of color ranging from white to deep pink, with many intermediate colors and patterns. Cornus florida ‘Cherokee Brave’, with deep pink bracts, and ‘Appalachian Spring’, with creamy white bracts, are two popular cultivars. A “pseudo-F2” population derived from these two cultivars lives at the UT Arboretum and segregates for leaf and bract color. Cornus kousa ‘K2’ is a vigorous tree that has been extensively used within the Rutgers’ University Woody Ornamental Breeding Program. Here, I developed genomic resources for these two species and implemented the flowering dogwood resources for identifying candidate genes involved in the regulation of bract and leaf color. Chromosome-scale, annotated, reference genomes were assembled for ‘Cherokee Brave’, ‘Appalachian Spring’, and ‘K2’. The genomic resources were then used to genotype the “pseudo-F2” population, quantify gene expression levels in both ‘Cherokee Brave’ and ‘Appalachian Spring’, and identify genomic variation. A 14 Mb locus associated with bract and leaf color was identified. Within this locus, 14 genes of interest were identified. Of the 14, two have differentially expressed genes between ‘Cherokee Brave’ and ‘Appalachian Spring’ and have variants with the expected inheritance pattern. The results and genomic resources developed here will be used to optimize breeding efforts for flowering and kousa dogwood.