Nuclear DNA content in some species of Lessingianthus (Vernonieae, Asteraceae) by flow cytometry

The nuclear DNA content was determined for the first time in 25 species of the South American genus Lessingianthus H.Rob. (Vernonieae, Asteraceae) by flow cytometry. This analysis constitutes the first estimation of the genome size for the Vernonieae tribe. The 2C- and 1Cx-values were calculated in all the species. The 2C-value ranged from 2.04 to 14.34 pg. The 1Cx-value ranged from 0.995 to 1.43 pg. The general tendency indicated a decrease in the 1Cx-value with increasing ploidy level, with some exceptions, in some species the 1Cx-value increased with the ploidy increase. The measuring of DNA content allowed reporting a new cytotype for L. polyphyllus (Sch.Bip.) H.Rob.     

Nuclear genome size variation in fleshy-fruited Neotropical Myrtaceae

In Myrtaceae, reports regarding the nuclear DNA content are scarce. The aim of this study is to present genome size data for fleshy-fruited Myrteae, and to test their relation with chromosome number and ploidy, the available data for cytoevolutionary studies in Myrtaceae. Thirty species out of ten genera were investigated for chromosome number and genome size using flow cytometry. Twenty-eight species were diploid with 2n = 2x = 22 and two species were tetraploid with 2n = 4x = 44. All genome sizes measured are new. Among the diploid species, a gradual and small variation in 2C-values (0.486 pg in Gomidesia schaueriana to 0.636 pg in Eugenia multicostata) was observed, whereas the tetraploid genomes of Psidium acutangulum and P. cattleianum had about twice as much DNA (1.053 and 1.167 pg, respectively). The total interspecific variation of C-values was 2.45-fold. The fleshy-fruited Myrteae have smaller holoploid genomes than the capsular-fruited Eucalypteae and Melaleuceae.     

Ploidy Level and DNA Content of Erianthus arundinaceus as Determined by Flow Cytometry and the Association with Biological Characteristics

Erianthus arundinaceus is not only an important germplasm resource for sugarcane breeding but also a potential bioenergy plant. Making clear the distribution of the chromosome ploidy of wild E. arundinaceus in china is the premise of the research and utilization of this species. Therefore, the objectives of this study were to determine the ploidy level and DNA content of the 55 E. arundinaceus accessions using flow cytometry and to identify the correlation between ploidy and phenotypic traits. Among the 55 accessions, four tetraploids and 51 hexaploids were identified. The four tetraploids originated from Mengma Yunnan, Shuangjiang Yunnan, Gaozhou Guangdong and Chengle Sichuan. The mean DNA content was 4.82 pg/2C for the tetraploid and 7.30 pg/2C for the hexaploid plants. The ploidy was negatively correlated with cellulose content and positively correlated (P<0.05) with plant height, stem diameter, leaf width, dry weight per plant, fresh weight per plant and hemicellulose content. However, ploidy was not correlated with leaf length, tiller number and the ratio of dry weight and fresh weight. This study will be useful for revealing the distribution of the ploidy of wild E. arundinaceus in Chin, traits markers analysis, and utilization of this species, such as cultivar improvement and sugarcane breeding in the future.     

The systematic value of nuclear genome size for “all” species of Tulipa L. (Liliaceae)

Nuclear genome size, as measured by flow cytometry with propidium iodide, was used to investigate the relationships within the genus Tulipa L. (Liliaceae). More than 400 accessions representing 123 taxa from mainly wild-collected plants were investigated. Most species of Tulipa have the same basic chromosome number, 2n = 2x = 24. However, the somatic DNA 2C value (2C) is shown to range from 32 to 69 pg for the diploids. The largest genome contains roughly 3.4 × 10¹⁰ more base pairs than the smallest and has chromosomes that are more than twice as large. These large differences in the amount of nuclear DNA predict that the hybrids, if any arise, are usually sterile. Depending on the size of the total genome, 1 pg amounts to several thousand genes. Moreover, genome sizes are evaluated here in combination with available morphological, geographical, and molecular data. Therefore, the taxonomy proposed here is not a single-character taxonomy based on genome size alone. The genus Tulipa, as here determined, has 87 species, 29 more than accepted by van Raamsdonk et al. [Acta Hort (ISHS) 430:821–828, 1997], but including 25 species that were not available to them. Of these 87 species, 28 were not seen by Hall (The genus Tulipa, The Royal Horticultural Society, London, 1940) in a living state and placed by him in an addendum. Species of the subgenus Clusianae (Baker) Zonn. differ strongly in nuclear DNA content (DNA 2C value), 32 versus 40–68 pg for all other tulips, and are placed here in a separate subgenus. Also Orithyia, the only group with a style and with only 38–39 pg is placed in a separate subgenus. Therefore, all tulips are attributed to four subgenera, Clusianae (Baker) Zonn., Tulipa, Eriostemones Raamsd., and Orithyia (D. Don) Baker and divided further into 12 sections. Seven of the eight series of section Eichleres (A.D. Hall) Raamsd. are now placed in four sections: (1) section Lanatae (Raamsd.) Zonn., mainly confined to species from the Pamir-Alay and including series Lanatae Raamsd., (2) section Multiflorae (Raamsd.) Zonn. (including series Glabrae Raamsd.), (3) section Vinistriatae (Raamsd.) Zonn. (including series Undulatae Raamsd.), and (4) section Spiranthera Vved. ex Zonn. and Veldk. Triploids, tetraploids, and pentaploids were found in several species. DNA content confirmed the close relationships of the species within the different sections. The rather similar looking and therefore often confused T. armena Boiss. (51.8 pg), T. systola Stapf (56.3 pg), and T. julia K., Koch (61.6 pg) could be clearly distinguished. The same is true for T. biebersteiniana Schult. f. (56.9 pg), T. sylvestris ssp. australis (Link) Pamp. (62.0 pg), and T. primulina Baker (64.6 pg). T. doerfleri Gand. and T. whittalli (Dykes) Hall could be placed as polyploid forms of T. orphanidea Boiss. ex Heldr. On the basis of DNA content, a systematic association between T. julia K. Koch and the triploid T. aleppensis Boiss. and between T. systola Stapf and the triploid T. praecox Tenore was suggested. The new species T. lemmersii Zonn., Peterse, and de Groot is described, and four possible new species are indicated. Genome size as measured by using flow cytometry may conveniently be used to produce systematic data. It is applicable even in the case of dormant bulbs or sterile plants for monitoring the trade in bulbous species.     

Molecular and Cytogenetic Characterization of Wild Musa Species

The production of bananas is threatened by rapid spreading of various diseases and adverse environmental conditions. The preservation and characterization of banana diversity is essential for the purposes of crop improvement. The world''s largest banana germplasm collection maintained at the Bioversity International Transit Centre (ITC) in Belgium is continuously expanded by new accessions of edible cultivars and wild species. Detailed morphological and molecular characterization of the accessions is necessary for efficient management of the collection and utilization of banana diversity. In this work, nuclear DNA content and genomic distribution of 45S and 5S rDNA were examined in 21 diploid accessions recently added to ITC collection, representing both sections of the genus Musa. 2C DNA content in the section Musa ranged from 1.217 to 1.315 pg. Species belonging to section Callimusa had 2C DNA contents ranging from 1.390 to 1.772 pg. While the number of 45S rDNA loci was conserved in the section Musa, it was highly variable in Callimusa species. 5S rRNA gene clusters were found on two to eight chromosomes per diploid cell. The accessions were genotyped using a set of 19 microsatellite markers to establish their relationships with the remaining accessions held at ITC. Genetic diversity done by SSR genotyping platform was extended by phylogenetic analysis of ITS region. ITS sequence data supported the clustering obtained by SSR analysis for most of the accessions. High level of nucleotide diversity and presence of more than two types of ITS sequences in eight wild diploids pointed to their origin by hybridization of different genotypes. This study significantly expands the number of wild Musa species where nuclear genome size and genomic distribution of rDNA loci is known. SSR genotyping identified Musa species that are closely related to the previously characterized accessions and provided data to aid in their classification. Sequence analysis of ITS region provided further information about evolutionary relationships between individual accessions and suggested that some of analyzed accessions were interspecific hybrids and/or backcross progeny.     

Genetic relations among basil taxa (Ocimum L.) based on molecular markers, nuclear DNA content, and chromosome number

Twenty-eight basil accessions including six Ocimum species and six botanical varieties or cultivars of O. basilicum were studied using molecular markers, nuclear DNA content, and chromosome counting. This is the first study reporting the nuclear DNA content in the genus Ocimum. The results supported the existence of more infrageneric groups within the genus. The section Ocimum was further divided into two separate clades. The first clade contained the accessions belonging to different botanical varieties and cultivars of O. basilicum as well as O. minimum, indicating that the separate species rank of O. minimum was not justified. The second clade, comprising O. americanum, O. africanum, and two O. basilicum var. purpurascens accessions, could represent a set of allopolyploid species sharing some common parental genomes. O. tenuiflorum was the most divergent species according to genetic distance; it had the smallest genome size, organized in small chromosomes, and the lowest chromosome number. Chromosome data obtained in our research could indicate that the basic chromosome number for species belonging to section Ocimum is x = 12. This suggestion implies that species belonging to O. basilicum clade are tetraploids, while species belonging to O. americanum clade are hexaploids. It seems that the basic chromosome number for O. gratissimum could be x = 10 and for O. tenuiflorum x = 9. The differences in genome size and chromosome number among Ocimum species indicate that evolution of their genomes was accompanied by both sequence deletion/amplification and chromosome rearrangements and polyploidization.     

Genome Size Evaluation in Tetraodontiform Fishes from the Neotropical Region

Smooth pufferfish of the family Tetraodontidae had become pure genomic models because of the remarkable compaction of their genome. This trait seems to be the result of DNA loss following its divergence from the sister family Diodontidae, which possess larger genomes. In this study, flow cytometry was used for estimate the genome size of four pufferfish species from the Neotropical region. Cytogenetic data and confocal microscopy were also used attempting to confirm relationships between DNA content and cytological parameters. The haploid genome size was 0.71?±?0.03 pg for Sphoeroides greeleyi, 0.34?±?0.01 pg for Sphoeroides spengleri, 0.82?±?0.03 pg for Sphoeroides testudineus (all Tetraodontidae), and 1.00?±?0.03 pg for Chilomycterus spinosus (Diodontidae). These differences are not related with ploidy level, because 46 chromosomes are considered basal for both families. The value for S. spengleri represents the smallest vertebrate genome reported to date. Since erythrocyte cell and nuclear sizes are strongly correlated with genome size, the variation in this last is considered under both adaptive and evolutionary perspectives.     

Regional Speciation or Taxonomic Inflation? The Status of Several Narrowly Distributed and Endangered Species of Narcissus Using ISSR and Nuclear Ribosomal ITS Markers

The mountains of the southeast Iberian Peninsula harbor several narrowly endemic species belonging to Narcissus section Pseudonarcissi (N. alcaracensis, N. bugei, N. enemeritoi, N. longispathus, N. nevadensis, N. segurensis, and N. yepesii) that are protected by regional Spanish laws. Most of these trumpet daffodils show a very similar overall morphology, and the correct identification of species is difficult unless the geographical origins of the accessions are known. ISSR (Inter-Simple Sequence Repeat) and nuclear ribosomal ITS sequences were used to assess patterns of genetic discontinuities present among the members of this section from southeast Spain. Species-specific ISSR bands were found in N. bugei, N. longispathus and N. nevadensis, but were absent in the other species. The multivariate ordination of the 288 ISSR-genotyped accessions showed that only N. longispathus and N. bugei were clearly differentiated, while the other species formed an unresolved group. ITS sequences of N. bugei were highly divergent from those retrieved from the remaining species, which were placed in a single largely unresolved clade in phylogenetic analysis. In conclusion, ISSR and ITS markers support the taxonomic distinction of N. bugei and N. longispathus. However, N. alcaracensis, N. segurensis, N. yepesii, N. enemeritoi, and N. nevadensis could be merged within a single species (N. nevadensis for nomenclatural priority).     

Genome size variation and morphological differentiation within Ranunculus parnassifolius group (Ranunculaceae) from calcareous screes in the Northwest of Spain

Ranunculus parnassifolius is an orophilous plant distributed throughout Central and Southwestern Europe (Alps, Pyrenees and Cantabrian Mountains). Its evolutionary history and taxonomy are often complicated, having been little studied before now. The purpose of this article is to present flow cytometry measurements and multivariate morphometric analyses to ascertain cytotype distribution patterns and the morphological differentiation of R. parnassifolius s.l. from calcareous screes in the Northwest of Spain. DNA ploidy level and morphometric analysis were determined for plants of R. parnassifolius s.l. using flow cytometry (112 individuals) and multivariate analysis (152 individuals). Specimens were collected in eight localities in the Northwest of the Iberian Peninsula. Different sample preservation methods (fresh, frozen, and herbarium specimens) were employed as well as the use of various buffers and internal standards, in order to test the reproducibility of DNA flow cytometry. Three ploidy levels were detected in the study area (diploid, tetraploid, and pentaploid), and mixed-cytotype populations were also found. The mean nuclear DNA content of the R. parnassifolius group ranged from 7.43 ± 0.185 to 7.63 ± 0.339 pg/2C in diploids and from 15.09 ± 0.161 to 15.85 ± 0.587 pg/2C in tetraploids. The analysis of the monoploid genome sizes (1Cx) did not reveal a clear difference among cytotypes. These results suggest low intraspecific variation, at least among the populations studied. In addition, a comparison of different DNA reference standards was conducted. A new value for the chicken genome size was used as internal reference standard (2C = 3.14 ± 0.155 pg), with similar results found using both animal and plant standards (Pisum sativum and Solanum lycopersicum). Finally, herbarium vouchers and frozen tissue were proved to be suitable for DNA ploidy level measurements. This study provided a first assessment of C values in the R. parnassifolius group using flow cytometry. The weak morphological distinction of the cytotypes and the existence of mixed-cytotype populations in the Northwest of Spain are reported here for the first time. The different distribution pattern of the two cytotypes is discussed.     

Genome size variation in Orchidaceae subfamily Apostasioideae: filling the phylogenetic gap

With more than 160‐fold variation, Orchidaceae are currently the most diverse angiosperm family with respect to the amount of nuclear DNA. This study provides first genome size estimates for approximately 50% of species currently recognized in subfamily Apostasioideae, which is sister to the other four orchid subfamilies. The estimated 1C‐values range from 0.38 pg in Apostasia nuda to 5.96 pg in Neuwiedia zollingeri var. javanica, a nearly 16‐fold range. The two genera show non‐overlapping genome sizes, with those in Apostasia being distinctly smaller than those in Neuwiedia. In fact, most Apostasia spp. are at the lower end of the range of orchid C‐values. Observed discontinuities in DNA amounts in genera most probably reflect interspecific variation in ploidy. In addition to ploidy heterogeneity in N. zollingeri var. javanica, intraspecific variation in genome size (up to 17.7%) was also detected in some species; this can be plausibly related to the incidence of different geographical variants or unrecognized taxonomic heterogeneity. The AT content varied from 62.6 to 66.0%, which is in the upper range recorded for angiosperms. The genome size data obtained in this study fill a major phylogenetic gap in Orchidaceae and show that (very) small genomes prevail in subfamily Apostasioideae. © 2013 The Linnean Society of London     

Correlation between nuclear DNA values and differing optimal ploidy levels inNarcissus,Hyacinthus andTulipa cultivars

4C nuclear DNA amounts were determined in 16 large decorative cultivars ofNarcissus (Amaryllidaceae), 13 ofHyacinthus (Hyacinthaceae) and 12 ofTulipa (Liliaceae) at different levels of ploidy. Within each genus, nuclear DNA amounts and ploidy levels are positively correlated, with no DNA loss in polyploids.Based on wide surveys of chromosome numbers, the maximum numbers of cultivars, interpreted as the optimum levels of selective success or horticultural fitness, were found to be at the tetraploid level inNarcissus (2n=4x=28), the triploid inHyacinthus (2n=3x=24) and the diploid inTulipa (2n=2x=24). All these ploidy optima were shown to correspond to a small range of nuclear DNA amounts (4C=96-139 pg), which could suggest the existence of a single DNA value optimal for the three biologically similar but unrelated genera. In each case the optimum is at an equilibrium reached between enhanced size and other morphological characteristics on one hand and reduced growth rate on the other, both resulting from increase in ploidy and nuclear DNA amounts.     

Flow cytometric analysis reveals different nuclear DNA contents in cultivated Fonio (Digitaria spp.) and some wild relatives from West-Africa

Nuclear DNA amounts of 118 cultivated fonio accessions representing 94 landraces collected from the major growing areas of West-Africa (Benin, Burkina Faso, Guinea, Mali and Togo) and eight accessions of four wild relatives were investigated by Laser flow cytometry. In cultivated species, average 2C-values ranged from 1.848 ± 0.031 pg for Digitaria iburua to 1.956 ± 0.004 pg for D. exilis. In D. exilis landraces the chromosome number was determined at 2n = 36. The closely related wild species D. longiflora and D. ternata showed similar 2C DNA contents of 1.869 ± 0.035 pg and 1.775 ± 0.070 pg, respectively. Distinctly larger genomes were identified for more distant species D. lecardii and D. ciliaris with 2.660 ± 0.070 pg and 2.576 ± 0.030 pg per 2C nucleus, respectively. Intra-specific variations were found to be slight and insignificant, suggesting genome size stability mainly within the cultivated gene pool. These results support the distance of cultivated fonio species D. exilis and D. iburua from D. lecardii and D. ciliaris as well as their close relationships with D. longiflora and D. ternata. Relevance of the results for ploidy level considerations in fonio millets is discussed.     

Population genetic structure of wild daffodils (Narcissus pseudonarcissus L.) at different spatial scales

We studied the population genetic and clonal structure of the endangered long-lived perennial plant Narcissus pseudonarcissus using random amplified polymorphic markers. Estimates for mean gene diversity within 15 populations of N. pseudonarcissus of three neighbouring geographical regions were high in comparison to other long-lived perennials (H _eN = 0.33). The genetic diversity of the two smallest populations (<200 plants) was significantly reduced, indicating loss of genetic variability due to drift. The analysis of the population genetic structure revealed a significant genetic differentiation both between regions (Φ_ST = 0.06) and between populations within regions (Φ_ST = 0.20). However, there was incomplete correspondence between geographical regions and the population genetic structure. In order to preserve the overall genetic variation in wild populations of N. pseudonarcissus, management measures should thus aim to protect many populations in each region. The spatial genetic structure within populations of N. pseudonarcissus was in agreement with an isolation by distance model indicating limited gene flow due to pollinator behaviour and restricted seed dispersal. The very restricted spatial extent of clonal growth (<5 cm) and the high level of clonal diversity indicate that clonal growth in N. pseudonarcissus is not an important mode of propagation and that management measures should favour sexual reproduction in order to avoid further reductions in the size and number of populations.     

Nuclear DNA content variation of three Miscanthus species in China

In order to estimate the variation in nuclear genome size in Miscanthus, flow cytometry of nuclei stained by propidium iodide was carried out using 36 populations of three Miscanthus species: M. lutarioriparius, M. sacchariflorus and M. sinensis, which were sampled from cold northern to warm and humid southern and central China, as well as near the sea level in eastern China to mountains in western China. The DNA content of diploid was 4.37 ± 0.02 pg/2C in M. lutarioriparius, 4.37 ± 0.01 pg/2C in M. sacchariflorus, and 5.37 ± 0.03 pg/2C in M. sinensis, respectively. There was no intraspecific variation in the three Miscanthus species at the diploid level, suggesting that the genome size was stable within species and the diverse environments did not induce variation in genome size at the diploid level. However, tetraploid populations were found in M. lutarioriparius and M. sacchariflorus, and their genome sizes were 8.56 and 8.54 pg, respectively, which are lower than expected values (8.74 pg), indicating the genome downsizing after polyploidization in the genus. Our results showed that the plant height of M. lutarioriparius was the highest one among the three species and the species was more closely related to M. sacchariflorus than M. sinensis. The intra-species genomic variation and inter-species differentiation in Miscanthus species provide important genetic and genomic information for the development of Miscanthus, especially for the endemic species, M. lutarioriparius, (together with Miscanthus × giganteus) which are now emerging as a key bio-energy crop because of their high yields and strong adaptability.     

Karyotype analysis and DNA content in some species of Chrysolaena (Vernonieae,Asteraceae)

Cytogenetic characterization by karyotyping and determination of DNA content by flow cytometry of five species of Chrysolaena (Vernonieae, Asteraceae) was performed. This is the first study of nuclear DNA content realized in the genus. The 2C-values were compared with the ploidy level and the total karyotype length (TKL) of each species. Mitotic analysis revealed a base chromosome number x = 10 for all entities and different ploidy levels, from diploid (2n = 2x = 20) to octoploid (2n = 8x = 80). All species showed bimodal karyotypes composed of metacentric and submetacentric chromosomes. The average chromosome size (ML) varied from 1.86 μm to 2.70 μm, while the TKL ranged from 18.65 μm to 80.55 μm. The intrachromosomal asymmetry index (A₁) varied from 0.27 to 0.38, while the interchromosomal asymmetry index (A₂) ranged from 0.19 to 0.25. A new cytotype is reported for the first time for C. propinqua. Accessory chromosomes found in C. verbascifolia, C. cognata, C. flexuosa, and C. propinqua are also reported as new.     

Flow cytometric measurements do not reveal different ploidy levels in Minthostachys (Lamiaceae)

Ten of the 17 species of the taxonomically difficult Andean mint genus Minthostachys (Lamiaceae) were submitted to flow cytometric measurements of nuclear DNA content to test the hypothesis of the occurrence of different ploidy levels within the genus. Nuclear DNA content was found to vary from 1.643 to 1.775 pg, i.e by only ca. 8% between individual accessions, thus providing no evidence for polyploidy in Minthostachys. While these results do not preclude the possibility that the genus contains polyploid species nor the occurrence of heteroploidy with nearly identical nuclear DNA contents, they suggest that polyploidy did not play a major role in its diversification.     

Genome sizes of all 19 Araucaria species are correlated with their geographical distribution

Nuclear genome size was determined to investigate the relationships between all 19 species of Araucaria de Jussieu. Species from the two other genera of Araucariaceae, Wollemia and Agathis, were also studied. The genome size of 17 out of the 19 species of Araucaria are reported here for the first time. All Araucariaceae have the same chromosome number 2n?=?26. However, the nuclear DNA contents (2C value) for Araucaria range from 31.3 to 45.4?pg. There is a good correlation between genome size and division in sections, and geographical distribution. The two species from South America have 44.7 and 45.4?pg, the two species from Australia have 35.7 and 44.4?pg and the two species from New Guinea 34.7 and 40.4?pg. All 13 species of New Caledonia and the one from Norfolk Island have a similar, if not identical, amount of nuclear DNA of, on average, 31.9?pg. This corroborates the identical DNA rbcL sequences found for the New Caledonian araucarias. It suggests that the species from New Caledonia diversified more recently and it questions their status as separate species. Compared with this 31.9?pg a strong increase seems to have occurred in the genome size of the “mainland” araucarias. Genome sizes are evaluated and compared with available taxonomic treatments and extant geographic spreading. The nuclear DNA contents found within the sections are close, making it possible to assign an unknown plant to a section. A difference of 1?pg, which amounts to a difference of 978?Mbp, far exceeds a single character. Nuclear DNA content, as measured by flow cytometry, may conveniently be used to produce systematic data. It is applicable even with young plants or seeds for monitoring the trade in endangered species.     

Cytogeography of Cenchrus ciliaris (Poaceae) in Tunisia

Belonging to the genus Cenchrus with 16–22 species, Cenchrus ciliaris L. (syn. Pennisetum ciliare (L.) Link, buffelgrass) is a perennial, common in warmer regions of both hemispheres, growing as a C4 grass in a wide range of habitats. In the present study we determined chromosome number and nuclear DNA content (2C DNA) for 28 natural populations collected from northern to southern Tunisia. Three ploidy levels were found: one tetraploid population (2n?=?4x?=?36), three pentaploid (2n?=?5x?=?45), and 24 hexaploid populations (2n?=?6x?=?54). The hexaploid chromosome number has already been reported for Tunisian populations of C. ciliaris but tetraploid and pentaploid (2n?=?45) are new for this area. The tetraploid population was found in the semi-arid north; pentaploids were mostly on the northern side of the arid region, while the hexaploids were located mainly in the arid southern Tunisian and Saharan region. 2C DNA values, assessed using flow cytometry, correlated with chromosome counts. Nuclear DNA content ranged from 2C?=?3.03 to 4.61 pg, revealing three ploidy levels corresponding to 4x, 5x, 6x, and mean 2C DNA amounts were of 3.03, 3.7 and 4.48 pg, respectively. Each cytotype produced viable pollen. Flow cytometric seed screening neither proved nor disproved apomixis. The most frequent hexaploid populations seem best adapted to arid conditions in southern Tunisia. The monoploid value, 1Cx, was constant. The existence of pentaploid cytotype suggests hybridization ability between tetraploids and hexaploids. It appears that polyploidization is the major evolutionary mechanism in the speciation of C. ciliaris.     

Change in nuclear DNA content and pollen size with polyploidisation in the sweet potato (Ipomoea batatas,Convolvulaceae) complex

• Genome size evolution and its relationship with pollen grain size has been investigated in sweet potato (Ipomoea batatas), an economically important crop which is closely related to diploid and tetraploid species, assessing the nuclear DNA content of 22 accessions from five Ipomoea species, ten sweet potato varieties and two outgroup taxa.
• Nuclear DNA amounts were determined using flow cytometry. Pollen grains were studied using scanning and transmission electron microscopy.
• 2C DNA content of hexaploid I. batatas ranged between 3.12–3.29 pg; the mean monoploid genome size being 0.539 pg (527 Mbp), similar to the related diploid accessions. In tetraploid species I. trifida and I. tabascana, 2C DNA content was, respectively, 2.07 and 2.03 pg. In the diploid species closely related to sweet potato e.g. I. ×leucantha, I. tiliacea, I. trifida and I. triloba, 2C DNA content was 1.01–1.12 pg. However, two diploid outgroup species, I. setosa and I. purpurea, were clearly different from the other diploid species, with 2C of 1.47–1.49 pg; they also have larger chromosomes. The I. batatas genome presents 60.0% AT bases.
• DNA content and ploidy level were positively correlated within this complex. In I. batatas and the more closely related species I. trifida, the genome size and ploidy levels were correlated with pollen size. Our results allow us to propose alternative or complementary hypotheses to that currently proposed for the formation of hexaploid Ipomoea batatas.

     

Ploidy levels among species in the 'Oxalis tuberosa alliance' as inferred by flow cytometry

The 'Oxalis tuberosa alliance' is a group of Andean Oxalis species allied to the Andean tuber crop O. tuberosa Molina (Oxalidaceae), commonly known as 'oca'. As part of a larger project studying the origins of polyploidy and domestication of cultivated oca, flow cytometry was used to survey DNA ploidy levels among Bolivian and Peruvian accessions of alliance members. In addition, this study provided a first assessment of C-values in the alliance by estimating nuclear DNA contents of these accessions using chicken erythrocytes as internal standard. Ten Bolivian accessions of cultivated O. tuberosa were confirmed to be octoploid, with a mean nuclear DNA content of approx. 3.6 pg/2C. Two Peruvian wild Oxalis species, O. phaeotricha and O. picchensis, were inferred to be tetraploid (both with approx. 1.67 pg/2C), the latter being one of the putative progenitors of O. tuberosa identified by chloroplast-expressed glutamine synthetase data in prior work. The remaining accessions (from 78 populations provisionally identified as 35 species) were DNA diploid, with nuclear DNA contents varying from 0.79 to 1.34 pg/2C.