Hybrids between Rubus idaeus and Rubus sect. Corylifolii and their relation to R. pruinosus and R. rosanthus

We have studied hybrids between Rubus idaeus and various members of R. Sect. Corylifolii, primarily in Sweden. With the help of DNA-ploidy level determinations using flow cytometry and microsatellite DNA analysis of over 500 samples, we show that the material can be divided into four stable apomictic species (belonging to Subsect. Subidaei) and a large number of primary hybrids. Stable species can be recognised by a distribution that is distinct from the Corylifolii parent, a uniform morphology and an almost invariant genetic pattern. We confirm that R. cordatiformis has arisen from the hybrid R. eluxatus idaeus. Moreover, our study shows that R. lagerbergii has arisen from the hybrid R. dissimulans idaeus. For R. onsalaënsis, we unexpectedly identify the Corylifolii ancestor as a previously unidentified blackberry with a very restricted distribution in the northern part of the province of Halland, which is here described as R. antecedens. Furthermore, we show that R. pruinosus s. str. has arisen from the hybrid R. aureolus idaeus and that it is known only from a rather restricted area in the provinces of Småland, Östergötland and Södermanland in eastern Sweden. On the other hand, the great majority of what has been called R. pruinosus is a diverse collection of primary hybrids between R. idaeus and various Corylifolii species, which show a large variation both genetically and morphologically. The same applies to R. rosanthus, which represents R. norvegicus idaeus hybrids: The microsatellite analysis shows that they have arisen independently and therefore should be considered as primary hybrids. We have identified primary hybrids between R. idaeus and R. gothicus (by far the most common hybrid in Sweden), R. aureolus, R. camptostachys, R. decurrentispinus, R. eluxatus, R. friesianus, R. hallandicus, R. lidforssii and R. norvegicus.