The Use of RAPDs for Assessment of Identity, Diversity, and Quality of Echinacea

The genus Echinacea, Asteraceae, is comprised of nine species, which are perennial herbs indigenous to North America and which have been traditionally used as medicinal plants for centuries. Three Echinacea species, E. angustifolia DC var. angustifolia, E. purpurea (L.) Moench, and E. pallida (Nutt.) Nutt., are currently being traded internationally in the natural products market. Echinacea products constitute a significant portion of this growing, multi-billion dollar industry. Echinacea is considered of value as a nonspecific immune stimulant; the pharmacological activity of Echinacea extracts has been widely studied with over 350 published studies to date (Briskin 2000) together providing strong evidence for an immune modulating activity of these extracts. The increasing popularity of Echinacea products has led to expansion in wildcrafting and commercial cultivation to meet the growing demand for plant material. Commercial supplies of E. purpurea are obtained from cultivated sources; E. angustifolia and E. pallida have until recently been supplied largely from indigenous habitats in the United States (Foster 1993). The threat to the genetic diversity present in wild populations due to indiscriminant overharvesting and the need for preservation of these genetic resources creates an incentive for the determination of the genetic variability present within these three species. The quality of botanical materials used in the manufacture of natural products has also been of concern with Echinacea products. Parthenium integrifolium is a common prairie perennial with a root morphology similar to that of E. angustifolia; roots of this plant have been a frequent adulterant of dried roots of E. angustifolia. DNA fingerprinting techniques such as random amplified polymorphic DNA (RAPD) (Williams et al. 1990) permit the identification of taxa and the determination of phylogenetic relationships and intraspecific diversity at a molecular genetic level. The use of such techniques for germplasm characterization facilitates the conservation and utilization of plant genetic resources, permitting the identification of unique accessions or sources of genetically diverse germplasm. The ability of this method to distinguish between taxa also has useful implications in botanical quality analysis. This study used RAPD markers to determine the genetic relationships of the three Echinacea species of commercial interest, to evaluate the level of diversity present within germplasm of each of the three species, and to compare accessions of each species available from different sources including the USDA National Plant Germplasm System and commercial sources. RAPD markers were also identified that are capable of distinguishing the presence of Parthenium integrifolium L., an adulterant of E. angustifolia, in DNA samples extracted from combined tissue of the two species. The 17 species-specific markers generated for the three Echinacea species in this study may also be useful in the identification of Echinacea species included in samples of botanical material or finished products.