Genetic structure of extant populations of Chrysanthemum arcticum L. and C. arcticum subsp. arcticum

Understanding the genetic diversity in natural plant populations is important to develop conservation strategies and utilize valuable germplasm resources. Chrysanthemum arcticum L., Arctic daisy (=Arctanthemum arcticum; =Dendranthema arcticum), and its two subspecies (C. arcticum L. subsp. arcticum and C. arcticum L. subsp. polaré Hultén) are the only Chrysanthemum species native to North America. We collected 529 individuals in nine C. arcticum and 21 C. arcticum subsp. arcticum populations from the state of Alaska mainland and Attu Island (the westernmost Aleutian Island). Evidence of declining population sizes and decreasing ranges of distribution were detected for both species and subspecies. Population genetic diversity was analyzed using 7449 single nucleotide polymorphism (SNP) markers developed using low-density DArTseq technology. Three distinct genetic clusters within C. arcticum populations were detected by STRUCTURE v.2.3.4, principal coordinate analysis, discriminant analysis of principal components, unweighted pair groupmethodwith arithmetic mean and SplitsTree. SNP data showed a clear taxonomic distinction among C. arcticum and C. arcticum subsp. arcticum. However, within C. arcticum subsp. arcticum populations, two subgroups occurred in the genetic cluster analyses that were a mixture of individuals from different populations, which may be the result of gene flow.