American ginseng (Panax quinquefolius L.) is an economically important perennial herb whose root is highly valued in the Orient for its medicinal properties. The root grows into different morphotypes, notably “bulb or round” (BLB), “man-like” (ML), and “straight or stick” (STK), and these roots are valued differently by consumers because they are assumed to have different medicinal qualities. Currently, wild-growing and field-cultivated plants are the major source of ginseng roots available on the market; however, because of declining wild populations and the lengthy time required in field cultivation to produce marketable root size, in vitro propagation has been sought as a potential alternative to supply ginseng's bioactive components (ginsenosides). The objectives of this study were: 1) to evaluate how explants derived from the three root morphotypes (lines), BLB, ML, and STK, responded to in vitro callus induction and growth; 2) to compare ginsenosides profiles and content among stock roots and their callus tissues; and 3) to assess genetic diversity among stock roots. Root explants were cultured on solid Murashige and Skoog medium supplemented with 1.0 mg·L−1 2,4-D and 0.1 mg·L−1 kinetin for 12 weeks. Explants from the three lines exhibited varied callus induction response, growth, and ginsenosides production. Explants from the ML line induced callus faster, were prolific in growth, and accumulated more biomass compared with explants from BLB and STK lines. ML lines (both stock roots and calluses) had significantly higher total ginsenosides content than either BLB or STK lines. There were positive and highly significant correlations between total ginsenosides content of stock roots and callus tissues and callus dry weights. Ginsenosides profiles varied among lines. ML lines exclusively exhibited low Rg1/high Re ginsenosides profiles, whereas BLB and STK lines exhibited mixed Rg1/Re profiles. Random amplified polymorphic DNA (RAPD) analysis of stock roots showed genetic variations within and among lines; however, there was no clear link between DNA bands or band patterns and ginsenoside profiles or content. Overall, these results showed that ginsenoside content of stock roots directly influenced callus induction response and subsequent callus biomass and ginsenoside content. These results provide information that could be useful in selecting suitable stock plants for in vitro production of ginsenosides. Also, because there are no ginseng cultivars, this information would be useful in advancing breeding efforts toward selecting superior cultivars for this species. Chemical names used: 2,4-dichlorophenoxyacetic acid (2,4-D)
Samuel G. Obae, Hillar Klandorf, and Todd P. West
Samuel G. Obae, Mark H. Brand, and Richard C. Kaitany
Japanese barberry (Berberis thunbergii DC.) is a popular ornamental shrub used in garden and urban landscaping. Currently there are over 60 B. thunbergii cultivars in the market. To better distinguish its cultivars, we used the amplified fragment length polymorphism (AFLP) technique to develop DNA marker profiles for 59 cultivars and hybrids. These markers were used to authenticate the trueness-to-name of B. thunbergii cultivars in production and in the market, control for intracultivar genetic variants, and develop a molecular key to identify cultivars approved for importation in Canada. Polymorphic markers from seven primer combinations were able to clearly differentiate 57 of 59 cultivars evaluated. Two cultivars, Aurea and Aurea Nana, could not be differentiated because they had identical marker profiles. Among the 274 plants tested, 263 were confirmed to be true-to-name and correctly labeled, whereas 11 plants could not be confirmed true-to-name. Seven of the 20 cultivars evaluated exhibited detectable intracultivar genetic variation. ‘Crimson Pygmy’ had the highest number of plants exhibiting genetic variability. Overall, nursery producers and retailers do not appear to be mixing or mislabeling cultivars. A molecular key developed from a subset of 25 markers was able to accurately identify and differentiate the 11 B. thunbergii cultivars approved for importation in Canada. This key could be used in a cultivar verification program to facilitate international trade of B. thunbergii cultivars where wheat rust is a concern.
Samuel G. Obae, Mark H. Brand, Bryan A. Connolly, Rochelle R. Beasley, and Stacey L. Lance
This study reports the development, characterization, and cross-species transferability of 20 genomic microsatellite markers for Aronia melanocarpa, an important nutraceutical fruit crop. The markers were developed with Illumina paired-end genomic sequencing technology using DNA from Professor Ed cultivar that was originally collected from the wild in New Hampshire. The markers were highly polymorphic and transferable to Aronia arbutifolia and Aronia prunifolia genomes. The average number of alleles per locus was 9.1, 4.5, and 5.6 for A. melanocarpa, A. arbutifolia, and A. prunifolia, respectively. The polymorphism information content (PIC) of loci ranged from 0.38 to 0.95 for all taxa, with an average of 0.80, 0.68, and 0.87 for A. melanocarpa, A. arbutifolia, and A. prunifolia, respectively. This is the first study to develop microsatellite markers in the Aronia genus. These markers will be very useful in studying the genetic diversity and population structure of wild Aronia and expediting the breeding efforts of this emerging fruit crop through marker-assisted selection.
Peter J. Leonard, Mark H. Brand, Bryan A. Connolly, and Samuel G. Obae
Aronia Medik., commonly known as chokeberry, is a genus of deciduous, multistemmed, rosaceous shrubs native to eastern North America. Three species of chokeberry are commonly accepted, A. arbutifolia (L.) Pers., red chokeberry, A. melanocarpa (Michx.) Elliott, black chokeberry, and A. prunifolia (Marshall) Rehder, or purple chokeberry. In Europe, a fourth species of human origin is recognized as Aronia mitschurinii A.K.Skvortsov & Maitul. In North America this type of Aronia is described as cultivars of A. melanocarpa, including ‘Viking’, ‘Nero’, and ‘Aron’. This species is characterized by near homogeneity of the population, tetraploidy, and a distinct morphology with more robust stems, wider leaf blades, and larger fruits than wild populations of A. melanocarpa. It has been proposed that this genotype originated from Russian pomologist Ivan Michurin’s early 20th century experiments involving Aronia × Sorbus hybridization. In this study we used amplified fragment length polymorphic (AFLP) markers to elucidate the relationships of A. mitschurinii to wild North American Aronia, ×Sorbaronia C.K. Schneid, Sorbus L., and six additional genera from subtribe Pyrinae (Rosaceae). Data from seven primer combinations were interpreted by the NTSYSpc software package into a similarity matrix using Jaccard’s coefficient. Clustering of AFLP similarity data using the unweighted pair group method with arithmetic mean (UPGMA) identified A. mitschurinii as distinct from wild Aronia, grouping it close to ×Sorbaronia fallax C. K. Schneid. and ×Sorbaronia ‘Ivan’s Beauty’. Non-metric multidimensional scaling (nMDS) also demonstrated a relationship between A. mitschurinii, ×Sorbaronia fallax, a ×Sorbaronia × Aronia backcross and compound-leaved Sorbus.