Hybrids between Rubus caesius and Rubus sect. Corylifolii (Rosaceae) and their relation to R. cyclomorphus, R. tiliaster, R. glauciformis, R. slesvicensis and R. firmus

Using flow cytometry and microsatellite DNA analysis (MSDA), we studied hybrids between Rubus caesius and various other Rubus species, with an emphasis on Sweden. We show that hybrids between Rubus caesius and Rubus sect. Corylifolii arise easily. They show a large variation in morphology, but can normally be recognised by a number of characters. They are typically hexaploids, but ~13% of the hybrids are pentaploids and ~8% tetraploids. With MSDA, they are harder to identify than hybrids with R. idaeus, partly because all Corylifolii species have themselves arisen from R. caesius hybrids and therefore share many alleles with R. caesius, partly because hybridisation with R. caesius seems to give rise to some variation in microsatellite regions. Hybrids with species of R. sect. Rubus are much rarer in Sweden and we have only identified one such case. We show that R. cyclomorphus and R. tiliaster are not proper apomictic species, at least not in Sweden, but rather a collection of genetical..., Five hundred seventy-six samples (young leaves from the tip of the annual shoot) of R. caesius, several Corylifolii species and putative R. caesius hybrids were collected, mainly from Sweden, but also from Denmark, Norway and Germany. The localities are specified in Table S1 in the Supplementary Material. Vouchers are deposited in LD. The samples were stored in a freezer at –80˚C until they were used. 
DNA was extracted with the 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 S2, were used to analyse variable microsatellite loci. The three loci Ru105b, Ru117b and Ru275a were described in R. idaeus (Graham et al. 2004), whereas the locus mRaCIRRIV2A8 was described in R. alceifolius Poir. (Ansellem et al. 2001). They will here be referred to as 105b, 117b, 275a and 2A8, respectively. They have been successfully used also for other ..., Data can be accessed using Ms Excel.