DNA fingerprint variation in some blackberry species (Rubus subg.Rubus,Rosaceae)

We have analysed samples from Sweden, Denmark, and Germany of six facultatively apomictic blackberry species to investigate the accordance between a taxonomy based on morphological characters on the one hand, and distribution of genetic variation estimated by DNA fingerprinting on the other hand. DNA fingerprint variation was found to be quite restricted in all species investigated. The first taxonomic group included three species related toRubus nessensis, two being characterized by one very widespread DNA fingerprint in all three countries and a few rare ones, whereas the third species differed between Sweden and Germany. The second taxonomic group included species related toR. gracilis. Two of these species exhibited very similar DNA fingerprints, whereas the third species deviated clearly. The utilization of DNA fingerprinting as a tool in taxonomy is discussed; most likely this method could become a useful complement to morphology, especially in plant groups with reduced levels of genetic recombination.     

Rubus vestervicensis (Rosaceae) — its hybrid origin revealed by DNA fingerprinting

Kraft, T., Nybom, H. & Werlemark, G. 199.5. Rubus vestervicensis (Rosaceae) — its hybrid origin revealed by DNA fingerprinting. — Nord. 3. Bot. 1.5: 237–242. Copenhagen. ISSN 0107-055X.
The large number of species in Rubus subgenus Rubus are thought to have arisen, at least in part, through hybridiation between facultatively apomictic species. R. vestervicensis is known only from a small island off the Swedish east coast. It has been suggested that it is a hybrid between R. grabowskii and R. pedemontanus . We have compared these species with DNA fingerprinting and our results support the hybridization hypothesis. All bands found in the fingerprint of R. grabowskii and about half of the bands found in R. pedemontanus were present in R. vestervicensis , suggesting that the latter species was derived from fertilization of an unreduced R. grabowskii egg cell with R. pedemontanus pollen.     

Pollen stainability variation in the apomictic blackberry, Rubus nessensis (Rosaceae)

Pollen quality was assessed with cotton blue staining in an apomictic blackberry, Rubus nessensis W. Hall, on plants grown outdoors in a random arrangement under uniform conditions. Significant variation between populations may be attributed mainly to genetical factors. Most of the variation found between plants, sometimes even between ramets, within a population must, however, be environmentally caused, likewise the variation between flowers within the same plant.     

Evidence of sexuality in European Rubus (Rosaceae) species based on AFLP and allozyme analysis

Reproduction of polyploid Rubus species is described as facultatively apomictic. Pollination is needed for seed set, but most seedlings are produced asexually by pseudogamy. Although sexual processes may occur, clonal diversity can be extremely low. We performed a pollination experiment to investigate the breeding system and used allozyme and AFLP markers to analyze genetic variation among and within seed families in R. armeniacus and R. bifrons. Pollination either with self or outcross pollen was necessary to trigger seed set. Outbreeding marginally increased the number and quality of seeds compared with selfing. The enzyme PGI revealed some genetic variation within seed families. Seven other enzyme systems were monomorphic. The more detailed AFLP analyses with five primer pairs detected the same rate of genetic variation (14-17% of seedlings were genetically distinct) and confirmed the allozyme results for the same individuals. No genetic variation was found between the seed families from within a species collected in widely separated populations, but clear species-specific differences were observed. The results support the view that polyploid Rubus species are pseudogamous apomicts with low genetic diversity among and within seed families. However, sexual reproduction occasionally occurs and contributes to the maintenance of genetic variation within natural populations.     

DNA fingerprinting reveals significant amounts of genetic variation in a wild raspberry Rubus idaeus population

Establishing the genotypic distribution in natural plant populations is an important part of ecological studies concerning plant growth, reproduction and turn-over. Restriction enzyme-digested DNA samples, isolated from 24 plants of a natural Rubus idaeus population, were analysed with DNA fingerprinting using the M13 repeat sequence as well as a synthetic (AC)/(TG) polydinucleotide as hybridization probes. All the examined samples exhibit unique DNA fingerprint patterns, suggesting that vegetative reproduction may be considerably more restricted in wild R. idaeus populations than previously assumed. By comparison, all samples of the apomictic blackberry species Rubus nessensis, collected on the same location, were completely identical.     

Patterns, sources and ecological implications of clonal diversity in apomictic Ranunculus carpaticola (Ranunculus auricomus complex, Ranunculaceae)

Sources and implications of genetic diversity in agamic complexes are still under debate. Population studies (amplified fragment length polymorphisms, microsatellites) and karyological methods (Feulgen DNA image densitometry and flow cytometry) were employed for characterization of genetic diversity and ploidy levels of 10 populations of Ranunculus carpaticola in central Slovakia. Whereas two diploid populations showed high levels of genetic diversity, as expected for sexual reproduction, eight populations are hexaploid and harbour lower degrees of genotypic variation, but maintain high levels of heterozygosity at many loci, as is typical for apomicts. Polyploid populations consist either of a single AFLP genotype or of one dominant and a few deviating genotypes. genotype/genodive and character incompatibility analyses suggest that genotypic variation within apomictic populations is caused by mutations, but in one population probably also by recombination. This local facultative sexuality may have a great impact on regional genotypic diversity. Two microsatellite loci discriminated genotypes separated by the accumulation of few mutations ('clone mates') within each AFLP clone. Genetic diversity is partitioned mainly among apomictic populations and is not geographically structured, which may be due to facultative sexuality and/or multiple colonizations of sites by different clones. Habitat differentiation and a tendency to inhabit artificial meadows is more pronounced in apomictic than in sexual populations. We hypothesize that maintenance of genetic diversity and superior colonizing abilities of apomicts in temporally and spatially heterogeneous environments are important for their distributional success.     

Patterns of genetic variation detected by RAPDs suggest a single origin with subsequent mutations and long-distance dispersal in the apomictic fern Dryopteris remota (Dryopteridaceae)

Debates on speciation processes in pteridophytes have revived. In order to study the evolutionary origin of an apomictic fern species, we investigated the genetic variation in the strictly agamosporous Dryopteris remota. We determined the genotypes of 22 individuals from many different locations within the species' European distribution and of 20 individuals from a Swiss population. A previous study on isozyme variation showed no intraspecific genetic variation in a similar sample set (Schneller and Holderegger, 1994, American Fern Journal 84: 94-98). In contrast to this, four out of 12 random amplified polymorphic DNA (RAPD) primers tested revealed low genetic diversity among individuals of D. remota from different locations. Intrapopulational genetic variation was also very low, but in the single population studied, a unique multiband genotype could be detected. The geographic distribution of genetic variation found in D. remota was best explained by the assumption of a single origin, the accumulation of somatic mutations during spread, and occasional, but effective, events of dispersal over large distances. The present study thus stresses the importance of long-distance dispersal in evolutionary processes and biogeography of ferns.     

DNA “FINGERPRINTS” REVEAL GENOTYPIC DISTRIBUTIONS IN NATURAL POPULATIONS OF BLACKBERRIES AND RASPBERRIES (RUBUS,ROSACEAE)

The genotypic distributions in a population of Rubus occidentalis L. and R. pensilvanicus Poiret were analyzed by using DNA “fingerprinting.” The number of genotypes found was related to the mode of reproduction; 20 plants of the sexual R. occidentalis comprised 15 genotypes, whereas 20 plants of the presumably apomictic R. pensilvanicus comprised only five genotypes. DNA “fingerprinting” appears to be a useful tool in the understanding of population structure.     

Evidence for a switch in the reproductive biology of Rubus alceifolius (Rosaceae) towards apomixis, between its native range and its area of introduction

We compared the reproductive system of Rubus alceifolius in its native range in Southeast Asia, in Madagascar, where the plant was introduced apparently some centuries ago, and in La Réunion, an Indian Ocean island onto which R. alceifolius was introduced (from Madagascan source populations) around 1850. While tetraploidy makes it impossible to analyze variation in R. alceifolius using classical methods of population genetics, both the patterns of genetic diversity (as revealed by AFLP [amplified fragment length polymorphism] markers) and differences between half-sib progeny and their maternal parents (revealed by microsatellite markers) show that in the plant's native range in southeast Asia, seeds are produced sexually. In contrast, in Madagascar sexual reproduction cannot alone account for the genetic patterns observed with microsatellite markers. Over 85% of the half-sib progeny resulting from open pollination gave multilocus genotypes identical to those of their respective maternal parents, despite the fact that the latter had alleles that were rare in the population. The other progeny differed in having an allele with one motif more or less than that of the maternal parent. Seeds thus appear to be produced mostly or exclusively by apomixis in Madagascar. We present findings suggesting that Madagascan populations result from hybridization of introduced R. alceifolius and native populations of R. roridus, a closely related species of Rubus subgenus Malachobatus, and suggest that apomixis was a consequence of this hybridization. In Reunionese populations of R. alceifolius (derived from Madagascan populations), seeds obtained in controlled pollination experiments were all genetically identical to maternal parents. While genetic variation (microsatellite markers) in Reunionese populations was low, it was sufficient to allow us to demonstrate that seeds could not have resulted from fertilization by the pollen donors chosen for controlled pollinations, or from autogamy, and were produced exclusively by apomixis.     

LIFE HISTORY VARIATION WITHIN POPULATIONS OF AN ASEXUAL PLANT,ERIGERON ANNUUS (ASTERACEAE)

Genetic variation was measured for several morphological and life history characters in Erigeron annum, a triploid and obligately apomictic species. There was significant genetic variation for nearly all characters measured, including plant size, growth rate, time of flowering, biomass allocation to roots and shoots, seed weight, and germination response to temperature. Variance among genotypes accounted for up to 55% of the total phenotypic variance, well within the range of heritabilities observed for sexual species. These estimates of broad-sense heritability predict substantial short-term response to selection on life history characters in this asexual species.     

Genetic diversity in sexual diploid and apomictic tetraploid populations of Paspalum notatum situated in sympatry or allopatry

Paspalum notatum is a subtropical grass widely distributed in the temperate areas of America. Diploids are sexual while polyploids give rise to clonal seeds through aposporous apomixis. RAPD markers were used to analyze the genetic structure of three natural populations: i) diploids reproducing sexually (R2X); ii) sympatric apomictic tetraploids collected in the vicinity of the diploids (R4X); iii) allopatric apomictic tetraploids growing in isolation (C4X). The apomictic reproduction rate was evaluated by the use of molecular markers in progeny tests, while chromosome-counting allowed the verification of ploidy levels. Data revealed that the R4X group presented a variation considerably higher than that observed for C4X. Jaccards coefficients were used to produce a cluster diagram using the UPGMA method. All but one tetraploid genotypes grouped together and were associated to diploid genotype A21. The possibility of occasional generation of novel tetraploid clones from the interaction between tetraploid and diploid individuals is discussed.     

Isozyme and morphological diversity within apomictic and sexual taxa of the Ranunculus auricomus complex

 In 17 populations of the tetraploid agamospecies R. variabilis, 10 enzyme systems have been studied by horizontal starch gel electrophoresis, and compared to previous data of 3 populations of the diploid sexual species R. notabilis. Allozymic and genotypic diversity of 12 polymorphic loci, and multilocus genotype diversity in R. variabilis compares to other apomictic taxa, confirming the assumed apomictic mode of reproduction previously found in 3 populations. A cluster analysis based on genetic distance values separated the two taxa, the populations of southeastern Austria sympatric with R. notabilis showing no closer relationships to the sexual species than the allopatric ones. The R. variabilis populations of the circumalpine regions are separated as a rather uniform group, those of the Bohemian massif as another, more heterogeneous group. This geographic differentiation is mainly due to genotypic variation, which is higher in the Bohemian massif than in the circumalpine group, and lower in areas where R. variabilis is sympatric with R. notabilis. Proportion of multilocus genotypes within populations (G/N), genotype diversity (D), and genotype evenness (E) measures indicate facultative recombination events with fixation and clonal reproduction of new recombined genotypes, which is regarded as the most important factor for the evolution of new lineages in goldilocks. Morphometric data of the R. variabilis and R. notabilis populations studied by cluster and principal coordinate analyses clearly separated the two taxa, and indicated a slight geographic differentiation with in R. variabilis corresponding to the results of isozyme data. A principal coordinate analysis of R. variabilis individuals based on stem and fruit characters showed a clinal variation, but no clear separation of groups. The variation found in this PCoA is almost completely covered from the most widespread clone (genotype I), and also from individual genotypes. The implications of the results on different species concepts for apomicts are discussed. For R. variabilis, no taxonomic conclusions can be drawn from the present data set. Received December 15, 1999 Accepted November 15, 2000     

Flowering and fruiting phenology in the apomictic blackberry, Rubus nessensis (Rosaceae)

Five stands of an apomictic blackberry, Rubus nessensis , were studied. Biennial shoots flower and fruit in their second year on lateral branches developed from axillary buds. Most premature death of reproductive units occurs by withering of entire laterals, presumably due to damage by frost during the preceeding autumn or winter. Health status of the floricane, assessed as percentage live axillary buds in the spring, was positively correlated with the reproduction parameters. Shoot height as well, is positively correlated with number of flower buds and flowers produced on each lateral but, however, negatively correlated with number of berries, probably because tall shoots tend to suffer more damage by frost which seriously afflicts the vascular tissues of the laterals.
The position of the axillary buds on the shoot affects survival and degree of fertility, those situated medially greatly surpassing apical and basal ones.     

A demographic study of the apomictic blackberry, Rubus nessensis (Rosaceae)

Ten stands of Rubus nessensis , an apomictic blackberry, were studied. Perennial stools produce biennial shoots that flower in their second year. The stools tend to produce shoots of similar height for several consecutive years. Flowering, but not relative fruit set, is dependent on shoot height. Shoot height and density appear to be positively related, implying that intraspecific competition is of little importance for plant vigour. Depletion time varies greatly between stands (4–29 years), being comparatively longer in stands with short shoots. New establishment is sparse and takes place mostly by root suckering.     

Selection on apomictic lineages of Taraxacum at establishment in a mixed sexual–apomictic population

A species’ mode of reproduction, sexual or asexual, will affect its ecology and evolution. In many species, asexuality is related to polyploidy. In Taraxacum, apomicts are triploid, and sexuals are diploid. To disentangle the effects of ploidy level and reproductive mode on life‐history traits, we compared established apomictic Taraxacum genotypes with newly synthesized apomictic genotypes, obtained from diploid–triploid crosses. Diploid–triploid crossing is probably the way that most apomictic lineages originate. New genotypes had on average a much lower seed set than established genotypes. Established genotypes differed on average from new genotypes, in particular under shaded conditions: the established genotypes had longer leaves and flowered later. The differences between new and established triploids resembled the differences that have been found between sexual diploids and established apomictic triploids. We conclude that ploidy differences alone are not directly responsible for observed differences between sexual diploid and apomictic triploid dandelions.     

Detection of quantitative trait loci for agronomic,yield, grain and disease characters in spring barley (Hordeum vulgare L.)

Quantitative trait loci (QTLs) have been revealed for characters in a segregating population from a spring barley cross between genotypes adapted to North-West Europe. Transgressive segregation was found for all the characters, which was confirmed by the regular detection of positive and negative QTLs from both parents. A QTL for all the agronomic, yield and grain characters measured except thousand grain weight was found in the region of the denso dwarfing gene locus. There were considerable differences between the location of QTLs found in the present study and those found in previous studies of North American germ plasm, revealing the diversity between the two gene pools. Thirty-one QTLs were detected in more than one environment for the 13 characters studied, although many more were detected in just one environment. Whilst biometrical analyses suggested the presence of epistasis in the genetic control of some characters, there was little evidence of interactions between the QTLs apart from those associated with yield. QTLs of large effect sometimes masked the presence of QTLs of smaller effect.     

Apomixis and sexuality in Paspalum simplex: characterization of the mode of reproduction in segregating progenies by different methods

Segregating progenies of crosses between sexual and apomictic genotypes of Paspalum simplex were analysed for the formation of meiotic versus aposporous embryo sacs, zygotic versus parthenogenetic embryos, and autonomous versus pseudogamous endosperms by using cytoembryological and flow cytometric analyses. Reduced and unreduced 8-nucleated embryo sacs were the final product of female gametophyte development in sexual and aposporous genotypes, respectively. An incomplete penetrance of parthenogenesis was detected in aposporous genotypes. The relative DNA content of endosperm nuclei revealed the normal 2:1 maternal to paternal ratio in sexuals and a 4:1 ratio in apomicts, indicating insensitivity of the apomictic genotypes to endosperm imprinting. Apospory, parthenogenesis and pseudogamy are located on a relatively large linkage group and are inherited together with previously developed molecular markers as a single genetic unit in segregating progenies.     

DNA fingerprinting—A useful tool in the taxonomy of apomictic plant groups

DNA fingerprinting has proved useful for the analysis of genotypic distribution and estimation of genetic relatedness in apomictic plant groups likeRubus, Amelanchier, Hieracium andTaraxacum. Speciation through interspectific hybridization has been demonstrated in one case involving apomicticRubus species. The application of molecular markers to progeny derived from experimental cross-pollinations has yielded information on levels of apomixis as well as on its inheritance and regulation in e.g.Rubus, Poa, Pennisetum andTripsacum.     

Molecular characterization of the Andean blackberry, Rubus glaucus, using SSR markers

The species Rubus glaucus, also known as the Andean or "Castilla" blackberry, is one of nine edible species of this genus that grow naturally in Central and South America. In Colombia, this species is the most important of all Rubus species for agricultural and commercial purposes. We used 20 SSRs developed for other Rubus species to characterize 44 Colombian R. glaucus genotypes, collected from eight different departments, and to look for molecular differences between thornless and thorny cultivated blackberries. Eighty-two bands were obtained from 28 loci. The genotypes were classified into eight populations, corresponding to collection sites. The mean number of polymorphic alleles per locus in all populations and genotypes ranged from 1.857 to 2.393. Samples collected from Valle del Cauca, Quindío, Caldas, and Risaralda departments had the highest heterozygosity values. The finding of exclusive bands from R. glaucus genotypes from Valle del Cauca, Quindío, and Caldas demonstrates genetic and molecular differentiation between thorny and thornless Andean blackberries.