Genetic and chemotypic diversity in American ginseng (Panax quinquefolius L.) from western North Carolina
American ginseng (Panax quinquefolius L.) is an herbaceous plant used medicinally in both North America, and more recently, Asia. Ginsenosides, the plant’s biologically active saponin glycosides, are used to treat conditions such as diabetes and cancer, and an individual plant’s suite of ginsenosides is termed its chemotype. Market demand for wild-grown plants has dramatically reduced population sizes, and P. quinquefolius has been listed on Appendix II of CITES since 1972. Loss of individuals has been correlated with reduced genetic variation within and among populations in some regions, but this relationship has not been well characterized in western North Carolina. Studies from other parts of ginseng’s range have also suggested relationships between genotypes and chemotypes, but these correlations have yet to be examined in the Southern Appalachians. We used 7 microsatellite loci to analyze DNA from 7 western North Carolina populations under different harvesting pressures, determining population-level genetic diversity and characterizing genotypes. Then, we used HPLC analyses to determine chemotypes and ginsenoside quantities for each genotyped plant. Finally, we correlated genetic and ginsenoside data for these plants.
As expected, measures of genetic variability were correlated with population size and harvesting pressure, with larger populations displaying significantly higher numbers of private alleles and degrees of heterozygosity (P < 0.05 for both). AMOVA showed that 79% of detected variation was among individuals within populations, suggesting historic or recent gene flow. Nei’s genetic distances were not always correlated with geographic distances, perhaps due to avian seed dispersal or harvester-mediated movements of adult plants. There was a significant relationship between population and total ginsenoside concentrations (P = 0.0001), and one ginsenoside species varied significantly by population (P = 0.0001). However, no alleles were significantly related to this ginsenoside (P > 0.05 for all), suggesting that population-level differences were due to environment rather than endogenous factors. Data from this study will inform the creation of domestic cultivars, significantly reducing the amount of wild P. quinquefolius needed to serve the Western market, and will inform efforts to conserve this ecologically and economically important species.