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Summary: Dogroses represent an exceptional system for studying the effects of genome doubling and hybridization: their asymmetrical meiosis enables recombination in bi‐parentally inherited chromosomes but prevents it in maternally inherited ones. We employed fluorescent in situ hybridization, genome skimming, amplicon sequencing of genomic and cDNA as well as conventional cloning of nuclear ribosomal DNA in two phylogenetically distinct pentaploid (2n = 5x = 35) species, Rosa canina and Rosa inodora, and their naturally occurring reciprocal hybrids, Rosa dumalis (5x) and Rosa agrestis (5x, 6x). Both progenitor species differed in composition, meiotic behaviour and expression of rDNA loci: R. canina (five 18S and 5–8 5S loci) was dominated by the Canina ribotypes, but R. inodora (four 18S loci and 7–8 5S loci) by the Rubiginosa ribotype. The co‐localized 5S/18S loci occurred on either bivalent‐forming (R. canina) or univalent‐forming (R. inodora) chromosomes. Ribosomal DNA loci were additively inherited; however, the Canina ribotypes were dominantly expressed, even in genotypes with relatively low copy number of these genes. Moreover, we observed rDNA homogenization towards the paternally transmitted Canina ribotype in 6x R. agrestis. The here‐observed variation in arrangement and composition of rDNA types between R. canina and R. inodora suggests the involvement of different genomes in bivalent formation. This results supports the hypothesis that the asymmetrical meiosis arose at least twice by independent ancient hybridization events. [ABSTRACT FROM AUTHOR]

Polyploid, hemisexual dogroses are known for their complicated reticulate evolutionary history and their ongoing hybridization events that challenge taxonomic concepts. We investigated how spontaneous hybrids between subsections Rubigineae and Caninae can be identified by cytological, genetic and morphological analyses and how they fit into the current taxonomic treatment. We sampled plants from mixed stands of both subsections in Germany and performed morphological measurements. We compared the morphological data with data from flow cytometry and microsatellite analyses compiled from a previous study based on a much wider sampling. Most of the investigated plants were pentaploid, but some species were composed of tetra- and hexaploid individuals co-occurring with the pentaploids. In Germany, all hexaploid plants were of hybridogenic origin and they were more frequently found in south-western Germany. Genetic and morphological data differentiated clearly between subsections and between informal aggregates of subsection Rubigineae. However, the currently accepted microspecies could be neither genetically nor morphologically unambiguously recognized. In contrast, multivariate analyses of genetic and morphological data distinguished between hexaploid and pentaploid cytotypes of the R. rubiginosa aggregate. The hexaploid hybridogenic individuals, mostly identified as R. micrantha, were characterized by more hairs and fewer glands on the leaflets and a smaller angle of the lamina base, characters typical for the paternal parent of subsection Caninae. [ABSTRACT FROM AUTHOR]

Premise of research. Spontaneous hybrids between species of Rosa sect. Caninae represent a unique example to study the genetic and epigenetic consequences of an imbalanced parental contribution to polyploid hybrids. Due to the unique canina meiosis, pentaploid or hexaploid dog rose hybrids contain a single subgenome transmitted by the haploid pollen grain of the paternal species and four to five subgenomes transmitted by the tetraploid or pentaploid egg cell of the maternal species. During this study, we investigated epigenetic changes in spontaneous reciprocal hybrids between the subsections Caninae and Rubigineae compared to their parental species in a natural population in eastern Germany. Methodology. For investigating epigenetic patterns, we applied cDNA--amplified fragment length polymorphisms (AFLPs) and methylation-sensitive amplified polymorphisms (MSAPs). Additionally, we analyzed micro-satellite data and measured morphological characters. Pivotal results. In line with expectations deduced from the genetic composition of the pentaploid and hexaploid hybrids, we observed a maternal bias of DNA methylation and expression patterns. We did not detect silencing of the respective paternal subgenomes. However, the percentage of paternally expressed fragments differed between plant organs. We found a higher number of paternally expressed fragments in sepals compared to leaves, suggesting that the parental genetic information underwent a rapid subfunctionalization in recently formed hybrids. Moreover, epigenetic data obtained from cDNA-AFLPs and MSAPs correlated stronger with morphology than with genetic data, based on microsatellites. Conclusions. The genetic contribution of subgenomes is strongly biased toward the maternal parent in dog rose hybrids, leading to a nearly apomictic mode of inheritance. However, we found that the underrepresented paternal genome is not silenced but transcribed and differentially expressed between plant organs. The correlation between epigenetic data and morphological data implies that the probably fast-evolving epigenetic changes have a major impact on dog rose phenotypes and may affect the establishment of hybrids in natural populations. [ABSTRACT FROM AUTHOR]