Polyploid Series Research Articles

Hybridization drives evolution of apomicts in Rubus subgenus Rubus: evidence from microsatellite markers.

Rubus subgenus Rubus is a group of mostly apomictic and polyploid species with a complicated taxonomy and history of ongoing hybridization. The only polyploid series with prevailing sexuality is the series Glandulosi , although the apomictic series Discolores and Radula also retain a high degree of sexuality, which is influenced by environmental conditions and/or pollen donors. The aim of this study is to detect sources of genetic variability, determine the origin of apomictic taxa and validate microsatellite markers by cloning and sequencing. A total of 206 individuals from two central European regions were genotyped for 11 nuclear microsatellite loci and the chloroplast trn L- trn F region. Microsatellite alleles were further sequenced in order to determine the exact repeat number and to detect size homoplasy due to insertions/deletions in flanking regions. The results confirm that apomictic microspecies of ser. Radula are derived from crosses between sexual series Glandulosi and apomictic series Discolores , whereby the apomict acts as pollen donor. Each apomictic microspecies is derived from a single distinct genotype differing from the parental taxa, suggesting stabilized clonal reproduction. Intraspecific variation within apomicts is considerably low compared with sexual series Glandulosi , and reflects somatic mutation accumulation. While facultative apomicts produce clonal offspring, sexual species are the conduits of origin for new genetically different apomictic lineages. One of the main driving forces of evolution and speciation in the highly apomictic subgenus Rubus in central Europe is sexuality in the series Glandulosi . Palaeovegetation data suggest that initial hybridizations took place over different time periods in the two studied regions, and that the successful origin and spread of apomictic microspecies of the series Radula took place over several millennia. Additionally, the cloning and sequencing show that standard evaluations of microsatellite repeat numbers underestimate genetic variability considering homoplasy in allele size.

The Reproductive Ecology of Diploid and Tetraploid Galax urceolata

Polyploidy is common in nature, particularly among plants, and is often associated with significant morphological, ecological, and evolutionary change. These changes may contribute to prezygotic and postzygotic isolation between cytotypes; therefore, polyploidy is commonly thought to lead to speciation. Recent work suggests prezygotic mechanisms may be more important in determining isolation than postzygotic mechanisms. We compared the reproductive ecology of populations of diploid and tetraploid Galax to assess the potential for gene flow between the cytotypes. Galax urceolata is native to the southern Appalachian Mountains and is a natural polyploid series with diploid, triploid, and autotetraploid individuals occurring in uniform and mixed-cytotype populations. We found the temporal peak of flower production in tetraploids slightly preceded that of diploids; however, the overall distributions of flowering phenologies were similar. Hymenoptera and Diptera were the most common floral visitors and diploids were visited slightly more often than tetraploids; however, there were no differences between cytotypes in terms of the taxonomic composition of their floral visitors. Seed production is likely pollen limited, but again this does not differ between cytotypes. While tetraploids produced more flowers than diploids, there was no difference in fruit production. Finally, our data suggest that Galax urceolata is self-incompatible. In sum we found few differences in the reproductive ecology of diploid and tetraploid Galax, which when combined with obligate outcrossing increases the potential for gene flow between cytotypes and reduces the likelihood of differentiation.

An Increasing Need for Productive and Stress Resilient Festulolium Amphiploids: What Can Be Learnt from the Stable Genomic Composition of Festuca pratensis subsp. apennina (De Not.) Hegi?

Genome composition of Festuca pratensis subsp. apennina (De Not.) Hegi, a tetraploid fescue species native to the tall forbs communities of south-eastern Europe at altitudes between 1100 and 2200m a.s.l. has been the subject of some debate by grass taxonomists. Our cytogenetic analyses including fluorescence in situ hybridisation with probes for genomic DNA and selected DNA repeats revealed the species to be allotetraploid and derived from interspecific hybridization between F. pratensis Huds., a species confined to grassland at lower altitudes, and a so far unknown Festuca species. Besides tetraploids, triploids and pentaploids were found growing in Alpine meadows in close association with F. pratensis subsp. apennina. Triploid cytotypes predominated at many sites in Switzerland and Romania, and in some localities, they were the only cytotypes observed. Cytogenetic analyses revealed the triploids to be hybrids between diploid F. pratensis and tetraploid Festuca pratensis subsp. apennina, while the pentaploid cytotypes originated from hybridization between F. pratensis subsp. apennina and hexaploid F. arundinacea Schreb., a closely-related species growing in a close vicinity to F. pratensis subsp. apennina. Parental genomes of F. pratensis subsp. apennina and of the triploid and pentaploid hybrids showed no evidence of homoeologous chromosome pairing and interspecific recombination, supporting previous observation of a disomic inheritance at meiosis, where chromosome pairing was restricted to bivalent associations. A hypothesis is presented that a chromosome pairing regulator(s), reported previously in other polyploid broad-leaved fescue species of the Festuca subg. Schedonorus, is present and functional in F. pratensis subsp. apennina. It is likely that a common ancestors’ genome that carries the chromosome pairing regulator(s) is present in all polyploid broad-leaved fescue species, and its acquisition was a key event that enabled speciation, and development of a polyploid series within Festuca. Identification of a functional chromosome pairing regulator capable of stabilizing advantageous genome combinations in hybrids within the Lolium-Festuca complex would greatly assist in development of stable Festulolium cultivars. Its expression within Festulolium amphiploid cultivars would assist strategies aimed at climate-proofing productive European grasslands to combat exposures to stress conditions.

Memoir on the origin of wheat stocks used by Prof. Tetsu Sakamura, on the centennial of his discovery of the correct chromosome number and polyploidy in wheat.

Sakamura (1918) reported the discovery of a polyploid series among eight species of the genus Triticum; this series consisted of 2x, 4x and 6x species with 2n = 14, 28 and 42 chromosomes, respectively. He mentioned in this article that all the materials he used were gifted by T. Minami of the same department of Hokkaido University, Japan. In addition to carrying out an extensive collection of cereal germplasms in the period 1914 to 1916, Minami wrote on October 7, 1915 to K. A. Flaksberger, a wheat taxonomist at the Bureau of Applied Botany, Saint Petersburg, Russia, requesting seeds of Russian wheat and other cereals. He sent Flaksberger a letter of acknowledgement for seed stocks on May 19, 1916; thus, the requested seed package must have arrived from Flaksberger at some time between October 7, 1915 and May 19, 1916. Based on the available documents, there was a considerable period of time between these seed stocks reaching Minami and Sakamura's publication of the chromosome numbers with the discovery of polyploidy. In fact, the wheat species identified by Flaksberger (1915) and those studied by Sakamura (1918) were identical except for two wild species which appeared only in Flaksberger's list. The available information supports a proposal that the wheat species used by Sakamura (1918) in his discovery of polyploidy, and later by Kihara (1924, 1930) in his genome analysis, originated from Flaksberger's collection.

How small and constrained is the genome size of angiosperm woody species

AbstractAngiosperm hardwood species are generally considered to show an average smaller genome size with a narrow range of variation than their herbaceous counterparts. Various explanations pertaining to limitations of cell size exerted by wood fibers, the requirement of smaller stomata, longer generation time, large population size, etc., have been put forward to account for their small and constrained genome size. Yet studies done in the past several years show that genomically as well as evolutionarily, hardwoods are as diverse and active as their herbaceous counterparts. This is entirely supported by the presence of well developed inter and intraspecific polyploid series and natural triploidy in many genera. Polyploidy, in some instances has been shown to confer adaptability to arid and salt stress conditions and in colonization of new areas. Moreover, hardwoods also show reasonable amenability to the induced polyploidy which abruptly changes the balance between nuclear and cell size. Polyploidy has been induced in many hardwoods to restore fertility in interspecific hybrids and for the production of triploids.Furthermore, some cases studied show that genome size variation in hardwoods can be as variable as that of herbaceous species. Genome size has been shown to vary remarkably both at homoploid level as well as by polyploidy in certain genera. In the same way, the genome size is not correlated with the habit in certain groups having both herbaceous and woody taxa. This point is further proved by the presence of secondary and insular woody habit in certain cases where either the transition to woodiness is not followed by any diminution in the genome size, or the genome size of insular woody species may be even more than that of the congeneric herbaceous species. This shows that woody habit does not by itself put any constraints on the genome size either at homoploid or at polyploidy levels. The genome size in fact, not only varies significantly in many congeneric woody species but also may not show any correlation with the habit when woody and herbaceous species are compared in some narrow taxonomic groups studied.

A comparison of plant chromosome number variation among Corsica, Sardinia and Sicily, the three largest Mediterranean islands

Chromosome counts of the vascular floras of Corsica, Sardinia, and Sicily were compared quantitatively, based on data stored in the online database “Chrobase.it”, and analysed to determine any trend associated to the latitudinal range. Mean chromosome number (CN) ± SD, frequency of B-chromosomes occurrence (fB), frequency of odd CN, and ICNH (Index of Chromosome Number Heterogeneity) were calculated for each island’s flora. The relative frequency of putative even ploidy levels was also calculated for the most frequent base numbers (x = 7, 8, 9) as the percentage of cytotype frequency value relative to the total sum of cytotypes. Our results show that ICNH and mean CN are lower in Sicily and higher in Sardinia and Corsica; furthermore, the relative frequencies of cytotypes of putative even polyploid series decrease with increasing ploidy levels, which can be modelled by an exponential decay of the general form f(x) = e(ax+b), with different parameters in the different islands. Such results are in agreement...

The Polyploid Series of the Achillea millefolium Aggregate in the Iberian Peninsula Investigated Using Microsatellites.

The Achillea millefolium aggregate is one of the most diverse polyploid complexes of the Northern hemisphere and has its western Eurasian boundary in the Iberian Peninsula. Four ploidy levels have been detected in A. millefolium, three of which have already been found in Iberia (diploid, hexaploid and octoploid), and a fourth (tetraploid) reported during the preparation of this paper. We collected a sample from 26 Iberian populations comprising all ploidy levels, and we used microsatellite markers analyzed as dominant in view of the high ploidy levels. Our goals were to quantify the genetic diversity of A. millefolium in the Iberian Peninsula, to elucidate its genetic structure, to investigate the differences in ploidy levels, and to analyse the dispersal of the species. The lack of spatial genetic structure recovered is linked to both high levels of gene flow between populations and to the fact that most genetic variability occurs within populations. This in turn suggests the existence of a huge panmictic yarrow population in the Iberian Peninsula. This is consistent with the assumption that recent colonization and rapid expansion occurred throughout this area. Likewise, the low levels of genetic variability recovered suggest that bottlenecks and/or founder events may have been involved in this process, and clonal reproduction may have played an important role in maintaining this genetic impoverishment. Indeed, the ecological and phenologic uniformity present in the A. millefolium agg. in Iberia compared to Eurasia and North America may be responsible for the low number of representatives of this complex of species present in the Iberian Peninsula. The low levels of genetic differentiation between ploidy levels recovered in our work suggest the absence of barriers between them.

Cytomixis in the cereal (Gramineae) microsporogenesis.

The specific features in behavior of the nuclei and chromatin migrating through cytomictic channels as well as in formation of micronuclei in the cereal microsporogenesis have been studied. Immunofluorescence microscopy has allowed for demonstration that the tubulin cytoskeleton does not play a significant role in the intercellular migration of nuclei. Potential involvement of the actin cytoskeleton and SUN-KASH linker complexes in cytomixis is discussed. Comparative analysis of the published and own data suggests that the cytological patterns of cytomixis in monocots and dicots are conserved. As has been shown, each higher ploidy level in the polyploid series of the family Gramineae is accompanied by an increase in the rate of cytomixis independently of individual species. The results confirm the assumption on a correlation between the rate of cytomixis, ploidy level, and genome balance.

Evolutionary site-number changes of ribosomal DNA loci during speciation: complex scenarios of ancestral and more recent polyploid events.

Several genome duplications have been identified in the evolution of seed plants, providing unique systems for studying karyological processes promoting diversification and speciation. Knowledge about the number of ribosomal DNA (rDNA) loci, together with their chromosomal distribution and structure, provides clues about organismal and molecular evolution at various phylogenetic levels. In this work, we aim to elucidate the evolutionary dynamics of karyological and rDNA site-number variation in all known taxa of subtribe Vellinae, showing a complex scenario of ancestral and more recent polyploid events. Specifically, we aim to infer the ancestral chromosome numbers and patterns of chromosome number variation, assess patterns of variation of both 45S and 5S rDNA families, trends in site-number change of rDNA loci within homoploid and polyploid series, and reconstruct the evolutionary history of rDNA site number using a phylogenetic hypothesis as a framework. The best-fitting model of chromosome number evolution with a high likelihood score suggests that the Vellinae core showing x = 17 chromosomes arose by duplication events from a recent x = 8 ancestor. Our survey suggests more complex patterns of polyploid evolution than previously noted for Vellinae. High polyploidization events (6x, 8x) arose independently in the basal clade Vella castrilensis-V. lucentina, where extant diploid species are unknown. Reconstruction of ancestral rDNA states in Vellinae supports the inference that the ancestral number of loci in the subtribe was two for each multigene family, suggesting that an overall tendency towards a net loss of 5S rDNA loci occurred during the splitting of Vellinae ancestors from the remaining Brassiceae lineages. A contrasting pattern for rDNA site change in both paleopolyploid and neopolyploid species was linked to diversification of Vellinae lineages. This suggests dynamic and independent changes in rDNA site number during speciation processes and a significant lack of correlation between 45S and 5S rDNA evolutionary pathways.

Rangewide ploidy variation and evolution in Acacia senegal: a north-south divide?

Knowledge of rangewide variation in DNA content and ploidy level may be valuable in understanding the evolutionary history of a species. Recent studies of Acacia senegal report diploids and occasional tetraploids in the Sudano-Sahelian region of sub-Saharan Africa, but nothing is known about the overall extent of DNA ploidy variation within the species. In this study, we determine the DNA content and ploidy level of A. senegal across its native range, and explore whether the variation is related to its evolutionary and colonization history. We used propidium iodide flow cytometry (FCM) to estimate DNA content (2C value) and infer ploidy in 157 individuals from 54 populations on various tissues, using seeds, fresh leaves, dried leaves and twigs and herbarium specimens. The mean 2C DNA (pg ± s.d.) contents detected were 1.47 ± 0.09, 2.12 ± 0.02, 2.89 ± 0.12, and a single individual with 4.51 pg, corresponding to a polyploid series of diploid, triploid, tetraploid and hexaploid individuals. Diploids were confirmed by chromosome counts (2n = 2x = 26). Most populations (90.7 %) were of single ploidy level, while mixed ploidy populations (9.3 %) comprising mostly diploids (2x+3x, 2x+4x and 2x+6x) were restricted to the Sudano-Sahelian and Indian subcontinent regions, its northern range. The species is predominantly diploid, and no mixed ploidy populations were detected in east and southern Africa, its southern range. The geographic pattern of ploidy variation in conjunction with existing phylogeographic and phylogenetic data of the species suggests that polyploids have occurred multiple times in its evolutionary and recent colonization history, including contemporary ecological timescales. The successful use of external tissues of dried twigs in FCM is new, and presents the opportunity to study numerous other dryland woody species.

Ploidy Levels and Pollen Stainability of Lantana camara Cultivars and Breeding Lines

Lantana camara L., a popular nursery and landscape plant, is categorized as an invasive species in Florida, because it produces viable pollen and cross-pollinates with the native species Lantana depressa Small. The invasive potential of L. camara is a challenging issue for the nursery and landscape industry, so sterile non-invasive cultivars are needed to replace fertile invasive ones. This study aimed to determine the ploidy level and male fertility of both commercial L. camara cultivars and breeding lines to identify male-sterile cultivars and assess the effectiveness of sterile triploid production in L. camara. A polyploid series was identified among 32 L. camara cultivars and breeding lines. Male fertility, based on pollen stainability, varied widely among the cultivars/breeding lines. Ploidy level was the most important factor determining L. camara pollen stainability/male sterility. On average, diploids exhibited the highest pollen stainability (64.6%) followed by tetraploids (45.1%), pentaploids (34.6%), and hexaploids (18.0%). Triploids showed the lowest pollen stainability (9.3%), suggesting that generating triploids would be an effective genetic approach to producing sterile L. camara and reducing its pollen-mediated invasiveness. Pollen stainability of triploid cultivars, Balandpawn (LandmarkTM Pink Dawn PP15,516), Lemon Drop, Miss Huff, New Gold, New Red Lantana, Red Butler, Red Spread Lantana, Samson Lantana, and Sunset Lantana was consistently below 10%. A number of triploid cultivars had pollen stainability approaching 20% to 30%, indicating a necessity for careful examination and screening of newly produced triploids to ensure high sterility in selected triploids. Pollen stainability variation was observed within ploidy levels, implying the existence of other genetic and environmental factors that influence the pollen stainability/male fertility of L. camara. Results from this study suggest that there is excellent potential to develop genetically sterile cultivars in L. camara for the U.S. nursery and landscape industry.

Variation in rDNA loci of polyploid Solanum elaeagnifolium (Solanaceae)

Fluorescence in situ hybridization (FISH) was applied to detect gene rearrangements and genome downsizing in Solanum elaeagnifolium, an invasive weed with 2n = 24, 48 and 72 populations. The probes employed were pTa71 containing the 18S–5.8S–26S gene, and a 5S rDNA probe obtained from S. stuckertii. As a result, diploids presented a pair of 18S–5.8S–26S signals and a pair of 5S, whereas tetra- and hexaploids increased their FISH marks proportional to the ploidy level. In all cases, rDNA loci were non-syntenic, and position was conserved along the polyploid series. The cytotypes would have formed recently and drastic rearrangements have not yet occurred. However, in each cell of the 4x and 6x individuals, signal intensity in one locus of the 18S–5.8S–26S was stronger, suggesting a potential loss of copies in the remaining loci. In addition, one hexaploid showed an extra 5S signal in heterozygosis. The data obtained suggest a recent, recurrent autopolyploidy.

Lippia alba (Verbenaceae): A new tropical autopolyploid complex?

• Premise of the study: Tropical regions have high species diversity, and polyploidization is a major mechanism of speciation in plants. However, few cases of natural polyploidy have been reported in tropical regions. Lippia alba, is a tropical, aromatic shrub with a wide distribution, extensive morphological plasticity, and several chemotypes. The species has long been recognized as a diploid with 2n = 30 chromosomes. Recently, two variations in chromosome number (2n = 60; 2n = 12-60) have been reported, suggesting the occurrence of polyploidy within the species.• Methods: Flow cytometry was used to investigate the genome size in 106 accessions from 14 Brazilian States. Conventional and molecular cytogenetic techniques and pollen viability analysis were employed to characterize each chromosome number observed.• Key results: The DNA 1C-value varied from 1.17 to 3.45 pg, showing a large variation in genome size. Five distinct chromosome numbers were observed (2n = 30, 38, 45, 60, 90); three are cytogenetically described here for the first time. The 5S rDNA signals varied proportionally according to each chromosome number, but 45S rDNA sites did not. High rates of meiotic irregularity were observed, mainly in cytotypes with higher chromosome numbers.• Conclusions: The data provide new support for the occurrence of a polyploid series in Lippia alba. We provide a hypothesis for how this complex may have arisen. Other cryptic polyploid complexes may remain undiscovered in tropical regions.

Gene Flow between Potato Cultivars under Experimental Field Conditions in Argentina

Wild and cultivated potatoes form a polyploid series with 2n = 2x to 2n = 6x (x = 12). In nature, they are separated by external and/or internal hybridization barriers that, when incomplete, provide opportunities for gene flow and introgression. Isolation distances estimated in one environment are not necessary extrapolable. As a starting point for pollen-mediated gene flow risk assessment in potatoes, an experiment was set up in the field in one of the major potato growing area in Argentina, with two pollen-pistil compatible tetraploid commercial cultivars with differential molecular marker patterns. The field design consisted of a 10 × 10 m central square with the pollen donor, surrounded by circles with a male sterile pollen recipient, set every 10 m up to 40 m. The crop was managed as a perennial, and data were recorded over 2 years. Seeded berries were obtained in both years at 30 and 40 m away from the center; all of them contained hybrid seeds as revealed by electrophoretic profiles. We consider that a minimal required isolation distance of 100 m or more would be more suitable for preventing undesirable gene flow in the area.

Genome size variation in guayule and mariola: Fundamental descriptors for polyploid plant taxa

Guayule (Parthenium argentatum A. Gray) has tremendous potential as a domestic source of natural rubber production in the southwestern United States. However, genetic improvement of guayule has been slowed by its complex mode of reproduction, natural ploidy series, and lack of genetic and genomic resources. The interspecific hybridization of guayule with its closest sister taxon mariola (P. incanum Kunth) offers an opportunity to access novel genetic variation for guayule breeding programs, but mariola accessions available from the U.S. National Plant Germplasm System (NPGS) have never been evaluated for natural variation in ploidy level. In addition, the nuclear genome sizes for guayule and mariola at any ploidy level are unknown. To that end, we examined the ploidy of 10 mariola accessions, which revealed a natural polyploid series ranging from triploid (2n=3x=54) to pentaploid (2n=5x=90). In contrast, a ploidy analysis of five guayule accessions uncovered a natural polyploid series that ranged from diploid (2n=2x=36) to hexaploid (2n=6x=108). More than one ploidy level among individual plants (mixed ploidy) and instances of aneuploid plants were observed for accessions of both guayule and mariola. The nuclear genome sizes of guayule and mariola were similar at identical ploidy levels, and the genome size of diploid guayule (1624Mb) was almost twofold smaller than the genomes of sunflower (H. annuus L. 2n=2x=34) and lettuce (L. sativa L.; 2n=2x=18), two other Compositae (Asteraceae) species that are being genome-sequenced. The results from this study will serve as a foundation for interspecific breeding and genome sequencing of guayule and mariola.

An overview of chromosome and basic numbers diversity in cytologically investigated polypetalous genera from the Western Himalayas (India)

Intensive exploration and evaluation of cytomorphological diversity has been carried out on 380 species of 127 genera belonging to 28 families of sub-class Polypetalae of flowering plants from Kashmir (Jammu and Kashmir) and Kangra and Sirmaur districts (Himachal Pradesh) of the Western Himalayas. The cytological investigations of these species over a period of three years revealed new and varied chromosome numbers for 100 species globally and 50 species in India, making a substantial addition to the knowledge of the genera to which these species belong. To obtain a comprehensive cytological picture of each of these genera, chromosomal data have been updated by compiling the literature on previous chromosomal numbers and supplementing it from the present studies. The final form is now ready to show the status both at global and Indian levels for various parameters like total number of taxonomically known species, number of cytologically determined species along with intraspecifically added number of cytological taxa, presently inferred basic numbers, level and frequency of polyploids, and information on number of species per genus carrying inter- and intraspecific euploid and aneuploid variability at the genus level. Of the total 127 genera, 39 genera have 75% or more cytologically worked out species. Addition of cytotypes in many cytologically known species has resulted in an enhanced number of chromosomal races/cytological taxa over such species, in the majority of genera, justifying the ever growing need to make population based intensive studies of any plant species. The data show that monobasic and dibasic genera are less common than tribasic and polybasic ones. Genera with x = 8 are most common, followed by x = 7 and x = 6. Of 127 genera, 47 genera exhibit polyploidy of up to 25%; 22 genera have 26–50%; 15 genera have 51–70%; and 26 genera have 76–100% polyploidy, while 17 genera lack polyploidy altogether. Interspecific and/or intraspecific euploid cytotypes such as diploids plus polyploids or with “polyploid series” are present in most of the 107 genera. Intraspecific aneuploid chromosome numbers are also shown by 100 genera. Since these genera belong to different families, so no generalization can be made at family level. However, at genus level chromosomal observations show the active role of various evolutionary processes responsible for chromosomal diversity in the majority of these genera distributed in the Western Himalayas of India.

Towards resolving the systematics ofCerastiumsubsectionCerastium(Caryophyllaceae): a cytogenetic approach

Analyses of mitotic chromosome numbers and nuclear DNA content were performed for 39 populations of 17 perennial Cerastium taxa from south-eastern Europe. The DNA content ranged from 2C = 2.43 to 8.78 pg, revealing four ploidy levels corresponding to 4x (2n = 36), 8x, 12x and 16x. High-polyploid cytotypes with a greater range of ploidy (up to 2n = 144) occur mostly in the central mountainous parts of the Balkan Peninsula. The chromosome number was determined for the first time for C. dinaricum (2n = 36 + 1B), C. decalvans subsp. orbelicum (2n = 36), C. decalvans subsp. glutinosum (2n = 36), C. neoscardicum (2n = 144), C. malyi subsp. serpentini (2n = 144) and C. moesiacum s.s. (2n = 144). New chromosome counts were recorded for C. arvense subsp. strictum (2n = 108), C. banaticum subsp. kosaninii (2n = 36) and C. grandiflorum (2n = 36). For the first time, flow cytometry was used to estimate C values for six species (15 taxonomic entities). The intraspecific variation quotient of C values is high, ranging from 1.003 in C. malyi to 1.306 in C. decalvans subsp. decalvans. The variation in chromosome size among both tetra- and octoploid members of Cerastium is much more prominent than in most other angiosperm polyploid series. Significant genome downsizing after polyploidization was observed in some investigated taxa. Differences in ploidy levels and monoploid genome size values confirm the taxonomic status of C. decalvans subsp. glutinosum and C. decalvans subsp. leontopodium. The results obtained indicate a possible close relationship between C. banaticum and C. grandiflorum, but not C. arvense.

A phylogenetic analysis of genus Onobrychis and its relationships within the tribe Hedysareae (Fabaceae)

Results about a phylogenetic analysis of the genus Onobrychis Mill., tribe Hedysareae DC. are presented. The systematic knowledge of tribe Hedysareae is still incomplete, with difficult circumscription of genera and species. Analyses were undertaken using both nuclear (ITS) and chloroplast (matK) markers for a set of 78 accessions covering 41 Onobrychis species, besides previously sequenced Hedysareae accessions. The phylogenetic methods used were maximum parsimony, maximum likelihood, and Bayesian analyses to produce phylogenetic trees and robustness indices. The genus Onobrychis was resolved as paraphyletic, with species of the genera Eversmannia Bunge and Hedysarum L. nested within it. The position of the section Membranacea of genus Hedysarum was as a sister group to Onobrychis and Eversmannia, separated from other accessions of Hedysarum. Variation in the 2 markers was sufficient to resolve infrageneric groups in Onobrychis and Hedysarum, but we were unable to completely resolve certain species in Onobrychis, particularly those within the sect. Onobrychis. The cause of this difficult species delimitation may be related to recent speciation, hybridization, and introgression events, particularly between cultivated species and their wild relatives, and the presence of cryptospecies as suggested by intraspecific polyploid series.

First record of a natural hexaploid population for Valeriana officinalis: genome size is confirmed to be a suitable indicator of ploidy level in the species

A recent study of genome size in Valeriana officinalis has established for a Pyrenean population a C-value divergent from those assessed in the currently known diploid, tetraploid and octoploid cytotypes, which proportionally indicates a hexaploid cytotype. If confirmed, this would constitute the first record of a natural hexaploid population for Valeriana officinalis. If not, these data would diminish the present strong support for accurate deduction of ploidy levels from genome sizes within the species. In order to discern between these two alternative interpretations, chromosome counts were carried out in the population of interest. Counting reveals 2n = 42, that is to say, the hexaploid cytotype. This result completes the polyploid series of V. officinalis and confirms the suitability of nuclear DNA amount for inferring ploidy level in the species. Such a finding raises the question of the origin and the extreme rarity of the hexaploid cytotype in V. officinalis. Furthermore, given that ploidy level i...

Physical mapping of 5S and 18S-5.8S-26S RNA gene families in polyploid series of Cenchrus ciliaris Linnaeus, 1771 (Poaceae)

The Buffelgrass (Cenchrus ciliaris L., Poaceae) is one of the most important pasturage grasses due to its high productivity and good forage qualities. This species possess a high adaptability to bioclimatic constraints of arid zones and may be used for the restoration of degraded arid ecosystems. Tunisian populations present three ploidy levels (4x, 5x and 6x) with a basic chromosome number x=9. This study reported for the first time the distribution of the ribosomal genes (rRNA) for pentaploid and hexaploid cytotypes of Cenchrus ciliaris. Molecular cytogenetic study using double fluorescence in situ hybridization has shown that the two rDNA families, 5S and 18S-5.8S-26S (18S), displayed intraspecific variation in number of loci among different ploidy levels. Each ploidy level was characterized by specific number of both 5S and 18S rDNA loci (two loci in tetraploid, five in pentaploid and six in hexaploid level). For three studied cytotypes (4x, 5x and 6x) all 5S rDNA loci were localized on the subcentromeric region of chromosomes, while 18S loci were situated on the telomeric region of short chromosome arms. Data of the FISH experiments show proportional increase of ribosomal loci number during polyploidization processes.