Genetic Structure and Population Differentiation of Chrysanthemum zawadzkii in Its Isolated European Range

This study investigated the genetic structure and diversity of Zawadzki's chrysanthemum (Chrysanthemum zawadzkii), a relict and endemic species with an isolated population in the Pieniny Mountains, Central Europe. The primary objective was to determine whether this population is genetically homogenous or consists of distinct subpopulations. To achieve this, plant material was collected from 13 sites across the Pieniny Mts. We used DArT-seq markers, including SNP and SilicoDArT, along with statistical methods like PCA, DAPC, and sNMF, to analyze the genetic data. The results demonstrated clear genetic differentiation within the population. Populations from the Trzy Korony (TK) and Macelowa Góra (MA) sites were genetically distinct from the others, which formed a more cohesive group. This genetic structure was confirmed by both PCA and DAPC analyses, which showed a separation of individuals and suggested limited gene flow. The analysis also indicated that a high number of clusters for SNPs (K=6) and a lower number for SilicoDArT (K=2) best described the genetic structure, revealing both a primary genetic division and more subtle substructures. Overall, the findings suggest that the genetic diversity of the Pieniny population is shaped by a combination of geographic, environmental, and historical factors. The observed differentiation, particularly in high-elevation populations like TK, MA, HA, and SK, is crucial for conservation efforts, highlighting the need to protect these genetically distinct groups to preserve the species' biodiversity and gene pool.