2018 ASHS Annual Conference

Asian dogwood (Cornus kousa), closely related to North America-native flowering dogwood (C. florida), is an economically important ornamental understory tree. Many C. kousa-based cultivars, breeding lines, and hybrids with C. florida have been developed and commercially released in the U.S.A. due to their attractive features and desirable (a)biotic stress tolerance. To assess the species genetic diversity, samples of C. kousa gDNA from 130 plants of non-cultivated Asian origin (China, Japan, Korea) were collected. Both living trees and herbarium specimens dated as early as 1950s were sampled. The collection was analyzed with PCR using 18 C. kousa-specific microsatellite markers and automated capillary gel electrophoresis. The dataset was then subjected to the population genetics analysis using R with several relevant packages. The majority of our dataset (locus- and population-wise) remained under the Hardy-Weinberg Equilibrium assumptions and showed high gene flow as expected from an obligate outcrossing species. Only negligible linkage disequilibrium was detected among the markers. Analysis of molecular variance indicated the overwhelming majority of variance partitioned among subpopulations and individuals. Among the five subpopulations (China current and old, Japan current and old, Korea old), the genetic variation accounted for 8.5% of total variation, yet demonstrated clear population structure according to the country of origin. Population structure was analyzed with both Bayesian and Discriminant Analysis of Principal Components approaches and indicated the presence of three population clusters matching the country of origin. Low genetic differentiation of our collection was attributed to the mutations accrued over time. The Neighbor-Joining tree of population distances indicated the samples from Japan as the most ancestral. This is to our knowledge the first detailed report on C. kousa population structure. Our results have important implications for future cultivar development, indicating that multiple sources of diversity may be used for breeding.