Genetic relationships among three native North-American Mahonia species, invasive Mahonia populations from Europe, and commercial cultivars

Horticulture is one of the most important pathways for plant invasion. We used microsatellite markers to reveal the impact of plant breeding on Mahonia aquifolium, an invasive ornamental shrub. Since it was bred by hybridization with the related species M. repens and M. pinnata, we compared populations of the three native species, various commercial cultivars and invasive populations. Invasive populations and cultivars were genetically differentiated from the native groups, but differences did not result from genetic bottlenecks. In cultivars but not in invasive populations, we proved genes from M. pinnata. No significant amount of M. repens genes were found in cultivars and invasive populations, but this result has to be viewed with caution because of the close relationship between native M. aquifolium and M. repens. We conclude that the evolution of invasive Mahonia populations was a result of restriction of gene pool during introduction, secondary release, and artificial selection, in combination with an increase of genetic diversity by plant breeders and by extensive gene flow.