Genetic differentiation over a spatial environmental gradient in wild Rubus ideaus populations.

•   The distribution is examined of molecular (random amplified polymorphic DNA) markers within and between 12 wild raspberry (Rubus ideaus) populations ranging over 600 m altitude and 40 km distance from a lowland area of extensive raspberry cultivation to remote upland sites. •   Most individuals are distinct, suggesting that seedling recruitment is the main means of propagation, but mean genetic similarities within sites (> 80%) are much greater than between sites (> 50%), suggesting a hindrance to gene movement between sites. •   Sites of genetically distinct populations can be grouped in lowland, valley and upland clusters; genetic similarity between sites decreased at slightly > 4% per 100 m difference in altitude from c. 80% between adjacent sites to 50% at 600 m altitude difference. •   Together with physiological data collected previously, the molecular evidence confirms that wild populations are more diverse than cultivars and suggests little gene flow from cultivated to wild, a result perhaps of reproductive asynchrony and little opportunity for seedling recruitment in established populations. The cause of the genetic differentiation between sites is not known and requires further study.