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. ..., Samples (young leaves from the tip of the annual shoot) were collected from R. idaeus, several Corylifolii species and putative hybrids were collected from Sweden. The localities are specified in the Supplementary Material and a number of vouchers are deposited in LD. The samples were stored in a freezer at –80˚C until they were used. 

DNA was extracted with the 2´ CTAB method (Doyle and Doyle 1987). The concentration of the DNA was determined by a fluorometer and the samples were diluted with ddH2O to ~14 ng/µL. Four pairs of microsatellite primers, described in Table 1, were used to analyse variable microsatellite loci. The three loci Ru105b, Ru117b and Ru275a were described for R. idaeus (Graham et al. 2004), whereas locus mRaCIRRIV2A8 was described from Rubus alceifolius(Ansellem et al. 2001). They will be called 105b, 117b, 275a and 2A8, respectively, in the following. They have also been successfully used also for other Rubus species (Stafne et al. 2005, Zhou 2014, Lewin 2016, ..., The readme file contains an explanation of each of the variable in the dataset (i.e. in the uploaded Excel file).