Chrysanthemum arcticum L. subsp. polaré is genetically distinct from other taxa in the Chrysanthemum arcticum species complex

The salt-tolerant “Chrysanthemum arcticum species complex” consists of three taxonomically distinct species/subspecies: C. arcticum, Arctic daisy (= Arctanthemum arcticum; = Dendranthema arcticum) and its two subspecies (C. a. subsp. arcticum, C. a. subsp. polaré). All are native to N. America with remnant populations also occurring in the Kamchatka Peninsula (Russian Federation) and Hokkaido, Japan. Each taxon and most populations are genetically distinct with little to no gene exchange, due to a lack of sympatry among species. Previous research found that single nucleotide polymorphisms (SNPs) clearly differentiated C. arcticum and C. a. subsp. arcticum as being taxonomically and genetically unique. However, the genetic structure of C. a. subsp. polaré populations and its relationship within the Chrysanthemum arcticum species complex is unknown. Our objectives were to determine the genetic structure of wild, geographically distinct C. a. subsp. polaré populations collected in Nome or Sitŋasuaq (Inupiaq), Unorganized Borough of Alaska (1 population; n=81 genotypes) and Churchill, Manitoba, Canada (20 populations; n=375 genotypes). Population genetic diversity was analyzed using 2113 SNP markers developed using low density DArTseq technology. Two distinct genetic clusters (delta K) within C. a. subsp. polaré sites were detected by STRUCTURE 2.3.4, principal coordinate analysis (PCoA), unweighted pair group method with arithmetic mean (UPGMA) and SplitsTree. SNP data showed a clear taxonomic distinction between the two geographic locations of C. a. subsp. polaré; all were also genetically distinct from C. arcticum and C. a. subsp. arcticum, based on 2,438 SNPs (n=989 genotypes). Principal component analyses (PCoA) had 31% of the genetic variation explained by PCoA1 (27%) and PCoA2 (4%) for the C. a. subsp. polaré sites. Ploidy levels and phenotypic traits will be integrated with the molecular data for future GWAS, QTL development and genome sequencing.