RAPD variation within and among natural populations of outcrossing willow-leaved foxglove (Digitalis obscura L.)

Random amplified polymorphic DNA (RAPD) markers were used to assess levels and patterns of genetic diversity in Digitalis obscura L. (Scrophulariaceae ), an outcrossing cardenolide-producing medicinal plant species. A total of 50 plants from six natural populations on the Iberian Peninsula were analy sed by six arbitrarily chosen decamer primers resulting in 96 highly reprod ucible RAPD bands. To avoid bias in parameter estimation, analyses of popul ation genetic structure were restricted to bands (35 of 96) whose observed frequencies were less than 1-3/n in each population. The analysis of molecu lar variance (AMOVA) with distances among individuals corrected for the dom inant nature of RAPDs (genotypic analysis) showed that most of the variatio n (84.8%) occurred among individuals within populations, which is expected for an outcrossing organism. Of the remaining variance, 9.7% was attributed to differences between regions, and 5.5% for differences among populations within regions. Estimates of the Wright, Weir and Cockerham and Lynch and Milligan F-ST from null-allele frequencies corroborated AMOVA partitioning and provided significant evidence for population differentiation in D. obsc ura. A non-parametric test for the homogeneity of molecular variance (HOMOV A) also showed significant differences in the amount of genetic variability present in the six populations. UPGMA cluster analyses, based on Apostol g enetic distance, revealed grouping of some geographically proximate populat ions. Nevertheless, a Mantel test did not give a significant correlation be tween geographic and genetic distances. This is the first report of the par titioning of genetic variability within and between populations of D. obscu ra and provides important baseline data for optimising sampling strategies and for conserving the genetic resources of this medicinal species.