Abstract

Samuel G. Obae and Todd P. West

Using random amplified polymorphic DNA (RAPD) markers, genetic variation and population structure of wild and cultivated American ginseng growing in West Virginia (WV) was assessed. Also, the effects of cultivation intensity and harvest pressure on genetic diversity of ginseng populations were evaluated. Eight primers were used to amplify DNA samples from 468 plants, generating a total of 98 band fragments of which 84 were polymorphic. Overall mean genetic diversity measures were lower in West Virginia populations compared to populations from Pennsylvania and Wisconsin. Among West Virginia populations, mean genetic diversity indices were higher in cultivated than in wild populations but differences were not significant. Means of genetic diversity indices were higher in wild populations from low harvest pressure region [percent polymorphism (P) = 33.33%, Nei's (1973) gene diversity (H) = 0.1172, and Shannon’s index (I) = 0.1743] compared to those from high harvest pressure region (P = 28.27%, H = 0.1019, I = 0.1513), however, these indices were not significantly different (P > 0.05, MannWhitney test). Analysis of molecular variance (AMOVA) however showed significant genetic differentiation (P < 0.001) within and among wild populations (48.37 and 54.10% respectively). Cultivated ginseng populations from a region with low cultivation intensity had lower levels of genetic diversity indices (P = 29.93%, H = 0.0948, I = 0.1609) compared to populations from a region with high cultivation intensity (P = 60.60%, H = 0.2593, I = 0.3243), these indices were significantly different (P < 0.05, MannWhitney test). AMOVA further revealed that in cultivated populations, 53.68 and 42.11% of the total genetic variation was attributed to within and among population differentiation in regions respectively and 4.20% of genetic variation existed between regions. Based on these data, it is evident that genetic diversity of American ginseng is substantially increased with increase in its cultivation intensity. This can be ascribed to higher levels of gene flow associated with sourcing of seeds from various sources to meet cultivation needs of large scale growers. Even though genetic variability among populations experiencing different harvest pressure was not statistically significant in this study, the lower genetic diversity indices exhibited in wild populations from high harvest pressure regions underscores the potential impacts of harvesting pressure on genetic diversity of this medicinal plant. Thus, the data presented in this study will be useful in guiding conservation strategies for this economically important but threatened medicinal species.