A new natural intergeneric hybrid — xDactylodenia vitosensis (Orchidaceae)

A new intergeneric hybrid ×Dactylodenia vitosensis Jagie??o (Dactylorhiza cordigera (Fries) Soó ×Gymnadenia conopsea (L.) R. Br.) is described. It was found in 1985 in the National Park of Mt. Vito?a near Sofia (Bulgaria, Eastern Carpathians, alt. 1550 m).     

Cephalostachyum chevalieri a new synonym of Kinabaluchloa wrayi (Poaceae: Bambusoideae), and a new bamboo record for Vietnam

Cephalostachyum chevalieri A. Camus is found to be a new synonym of Kinabaluchloa wrayi (Stapf) K. M. Wong, extending the species range from the Malay Peninsula to Vietnam. Its type, Chevalier 4485, and other specimens collected from the type locality, have the same culm leaf, pseudo‐spikelet and flower characteristics as K. wrayi.     

Rapid diversification by recombination in Bartonella grahamii from wild rodents in Asia contrasts with low levels of genomic divergence in Northern Europe and America

Bartonella is a genus of vector‐borne bacteria that infect the red blood cells of mammals, and includes several human‐specific and zoonotic pathogens. Bartonella grahamii has a wide host range and is one of the most prevalent Bartonella species in wild rodents. We studied the population structure, genome content and genome plasticity of a collection of 26 B. grahamii isolates from 11 species of wild rodents in seven countries. We found strong geographic patterns, high recombination frequencies and large variations in genome size in B. grahamii compared with previously analysed cat‐ and human‐associated Bartonella species. The extent of sequence divergence in B. grahamii populations was markedly lower in Europe and North America than in Asia, and several recombination events were predicted between the Asian strains. We discuss environmental and demographic factors that may underlie the observed differences.     

Evolutional and Geographical Relationships of <Emphasis Type="Italic">Bartonella grahamii</Emphasis> Isolates from Wild Rodents by Multi-locus Sequencing Analysis

To clarify the relationship between Bartonella grahamii strains and both the rodent host species and the geographic location of the rodent habitat, we have investigated 31 B. grahamii strains from ten rodent host species from Asia (Japan and China), North America (Canada and the USA), and Europe (Russia and the UK). On the basis of multi-locus sequencing analysis of 16S rRNA, ftsZ, gltA, groEL, ribC, and rpoB, the strains were classified into two large groups, an Asian group and an American/European group. In addition, the strains examined were clearly clustered according to the geographic locations where the rodents had been captured. In the phylogenetic analysis based on gltA, the Japanese strains were divided into two subgroups: one close to strains from China, and the other related to strains from Far Eastern Russia. Thus, these observations suggest that the B. grahamii strains distributed in Japanese rodents originated from two different geographic regions. In the American/European group, B. grahamii from the North American continent showed an ancestral lineage and strict host specificity; by contrast, European strains showed low host specificity. The phylogenetic analysis and host specificity of B. grahamii raise the possibility that B. grahamii strains originating in the North American continent were distributed to European countries by adapting to various rodent hosts. An erratum to this article can be found at     

Studies on genetic diversity and phylogenetic relationships of limpograss (Hemarthria altissima) and related species based on combined chloroplast DNA intergenic spacer data

Hemarthria R. Br. is a genus which includes important forage grasses. However, there is currently a lack of data analysis on the chloroplast DNA (cpDNA) of Hemarthria species. This study is to use three cpDNA intergenic spacers (trnL-F, trnC-ycf6 and psbC-trnS) to obtain phylogenetic information in 36 Hemarthria samples including four Hemarthria species: Hemarthria altissima (Poir.) Stapf et C. E. Hubb., Hemarthria compressa (L. f.) R. Br., Hemarthria uncinata R. Br., and Hemarthria japonica (Hack.) Roshev. Data analysis revealed that non-significant genetic diversity existed in our samples, which was implied by nucleotide sequences information and the results of haplotypic and nucleotide diversity. The results of phylogenetic trees based on maximum likelihood (ML) and Bayesian inference (BI) revealed that H. altissima and H. compressa samples were not entirely distinct, suggesting that the two species share an intimate genetic relationship. A haplotype median-joining (MJ) network revealed broadly similar results to those derived from the ML and BI trees and implied that haplotype H3 may represent an ancient haplotype. Analysis of the population statistic F_ST revealed little genetic differentiation among the seven populations of H. altissima in Africa.     

Intergeneric hybridization between Erucastrum canariense and Brassica rapa. Genetic relatedness between E(C) and A genomes

An intergeneric hybrid between a wild species, Erucastrum canariense (2n = 18; E^CE^C), and a cultivated oilseed brassica species, Brassica rapa (2n = 20; AA), was synthesized through ovary culture in White's basal medium supplemented with casein hydrolysate. Morphological, cytological and DNA-based analysis helped to establish the hybrid nature of the derived plants. Hybrid plants were morphologically intermediate between the two parents and were completely male, as well as female sterile. Cytological analysis revealed the occurrence of 19 I in about 38% of the PMCs investigated. However 1-8 bivalents/PMC were also observed, indicating a significant level of homology between the two genomes. Normal chromosome pairing and pollen fertility was restored following colchiploidy. The intergeneric amphiploid developed during the investigation can be used as a bridging species for the transfer of desirable genes from E^C to cultivated genomes (especially A and C), and for resistance to Alternaria blight and mustard aphid. Under field conditions, the E. canariense intergeneric hybrid and the amphiploid appeared to be moderately resistant to Alternaria blight and also harboured a significantly lower population of mustard aphid than the cultivated B. rapa.     

Cytogenetic relationships,polyploid origin and taxonomic issues in Paspalum species: inter‐ and intraspecific hybrids between a sexual synthetic autotetraploid and five wild apomictic tetraploid species

• Paspalum is a noteworthy grass genus due to the forage quality of most species, with approximately 330 species, and the high proportion of those that reproduce via apomixis. Harnessing apomictic reproduction and widening knowledge about the cytogenetic relationships among species are essential tools for plant breeding.
• We conducted cytogenetic analyses of inter‐ and intraspecific hybridisations involving a sexual, colchicine‐induced autotetraploid plant of P. plicatulum Michx. and five indigenous apomictic tetraploid (2n = 40) species: P. compressifolium Swallen, P. lenticulare Kunth, two accessions of P. nicorae Parodi, P. rojasii Hack. and two accessions of P. plicatulum. Fertility of the hybrids was investigated and their reproductive system was analysed considering the relative embryo:endosperm DNA content from flow cytometry. Morphological, nomenclatural and taxonomic issues were also analysed.
• Cytogenetic analysis suggested that all indigenous tetraploid accessions of five apomictic species are autotetraploid or segmental allotetraploid. If segmental allotetraploids, they probably originated through autoploidy followed by diploidisation processes. Autosyndetic male chromosome pairing observed in all hybrid families supported this assertion. Allosyndetic chromosome associations were also observed in all hybrid families. In the hybrids, the proportion of male parent chromosomes involved in allosyndesis per pollen mother cell varied from 5.5% to 35.0% and the maximum was between 25% and 60%. The apomictic condition of the indigenous male parents segregated in the hybrids.
• These results confirm a strong association between autoploidy and apomixis in Paspalum, and the existence of cytogenetic relationships between different species of the Plicatula group. Allosyndetic chromosome pairing and seed fertility of the hybrids suggest the feasibility of gene transfer among species.

     

DNA CONTENT OF SEVEN SPECIES OF ASTEREAE AND ITS SIGNIFICANCE TO THEORIES OF CHROMOSOME EVOLUTION IN THE TRIBE

Relative amounts of nuclear DNA were determined in root tip cells of seven species of Astereae: Aster hydrophilus Greene, A. oblongifolius Nutt., A. riparius H.B.K., Machaeranthera boltoniae (Greene) Turner and Home, M. brevilingulata (Sch-Bip.) Turner and Home, M. parviflora Gray, and M. tenuis (S. Wats.) Turner and Home. The results show that A. hydrophilus and M. brevilingulata, with a chromosome number of n = 9, have less nuclear DNA than other closely related species which are either n = 4 or n = 5. Cytological analyses of meiosis in the intergeneric hybrid M. parviflora X A. hydrophilus showed cells with two or more small chromosomes of the latter species pairing with single large chromosomes of the former. Pachytene cells of the hybrids M. parviflora X A. hydrophilus, M. parviflora X A. riparius, and M. boltoniae X M. tenuis showed some unpaired chromosome segments. The significance of these results to chromosome evolution in the tribe Astereae is discussed.     

Physical mapping of rDNA genes corroborates allopolyploid origin in apomictic Brachiaria brizantha

Brachiaria (Trin.) Griseb belongs to the family Poaceae, and within the genus, apomixis or sexuality is present in different accessions of the same species. The majority of Brachiaria species are polyploid and apomictic, making strategies for crop improvement by breeding very intricate. In spite of the high frequency of apomictic polyploids, the relationship of polyploidy and hybridization with apomixis in Brachiaria is still unclear. Further analysis requires detailed knowledge regarding the genomic composition of the polyploids. The present work introduces the use of fluorescent in situ hybridization (FISH) into cytogenetic analysis of Brachiaria. Physical mapping of heterologous rDNA sequences, associated with conventional karyotyping of the B. brizantha diploid sexual (BRA 002747) and the tetraploid apomictic (BRA000591) accessions, provided evidence of the latter being of allopolyploid origin. Based on our results and on previous knowledge on apomixis in B. brizantha, we suggest that the origin of apomixis was probably a consequence of hybridization.     

Description of a fertilization-independent obligate apomictic species: Corunastylis apostasioides Fitzg

The Australian midge orchid Corunastylis apostasioides of the tribe Diurideae has completely eliminated any male contribution in the process of seed formation, which occurs directly from the maternal tissue by a process termed apomixis. Here, we report C. apostasioides to be an obligate apomictic species devoid of any sexuality and compare its development to a close sexual relative C. fimbriata (R. Br.) D.L. Jones & M.A. Clem. Apomictic characteristics in C. apostasioides include production of seed in absence of fertilization, frequently closed flowers, production of immature pollen in non-dehiscent anthers, expansion of ovaries despite the lack of fertilization and the absence of a citronella scent that is found in C. fimbriata produced to attract pollinating vinegar flies (Jones 2006). The nature of apomixis in C. apostasioides was examined by ovule histology and amplified fragment length polymorphism (AFLP) in each case drawing comparison with sexual C. fimbriata. In C. apostasioides the central megaspore mother cell undergoes diplosporic apomixis, while additional embryos are derived from nucellar or integument initials formed by sporophytic apomixis. Typical of apomicts, C. apostasioides is polyploid compared to the sexual C. fimbriata. The divergences of C. apostasioides from sexuality to apomictic development are discussed.     

Pollination biology of annual and perennialLeonotis species (Lamiaceae)

The pollination syndromes ofLeonotis (Pers.)R. Br. are discussed. Ornithophily accounts for most of the nutlets set in perennialLeonotis species but in the annual species [L. nepetifolia (L.)R. Br.] autogamy prevails.Leonotis species are predominantly pollinated by a variety of sunbirds, although bees are also involved. Nectar is sucrose-dominant in perennial species but hexose-dominant in the annual.     

Crossing the divide: gene flow produces intergeneric hybrid in feral transgenic creeping bentgrass population

Gene flow is the most frequently expressed public concern related to the deregulation of transgenic events ( Snow 2002 ; Ellstrand 2003 ). However, assessing the potential for transgene escape is complex because it depends on the opportunities for unintended gene flow, and establishment and persistence of the transgene in the environment ( Warwick et al. 2008 ). Creeping bentgrass (Agrostis stolonifera L.), a turfgrass species widely used on golf courses, has been genetically engineered to be resistant to glyphosate, a nonselective herbicide. Outcrossing species, such as creeping bentgrass (CB), which have several compatible species, have greater chances for gene escape and spontaneous hybridization (i.e. natural, unassisted sexual reproduction between taxa in the field), which challenges transgene containment. Several authors have emphasized the need for evidence of spontaneous hybridization to infer the potential for gene flow ( Armstrong et al. 2005 ). Here we report that a transgenic intergeneric hybrid has been produced as result of spontaneous hybridization of a feral‐regulated transgenic pollen receptor (CB) and a nontransgenic pollen donor (rabbitfoot grass, RF, Polypogon monspeliensis (L.) Desf.). We identified an off‐type transgenic seedling and confirmed it to be CB × RF intergeneric hybrid. This first report of a transgenic intergeneric hybrid produced in situ with a regulated transgenic event demonstrates the importance of considering all possible avenues for transgene spread at the landscape level before planting a regulated transgenic crop in the field. Spontaneous hybridization adds a level of complexity to transgene monitoring, containment, mitigation and remediation programmes.     

THE RELATIONSHIP AND ORIGIN OF TSUGA HETEROPHYLLA AND TSUGA MERTENSIANA BASED ON PHYTOCHEMICAL AND MORPHOLOGICAL INTERPRETATIONS

Morphological intermediacy between Tsuga heterophylla and Tsuga mertensiana has stimulated controversy concerning the relationship between these two hemlock species and has led to wide acceptance of hybridization as a causative factor of intermediate forms in areas of distributional overlap. In this study, comparative’ chemical analyses were used to test the theory of hybrid derivation of intermediates. Chromatographic analyses were further applied to the phylogenetic ranking of several North American and Asian species of Tsuga and to the examination of the hypothesis that Tsuga mertensiana is a derivative of intergeneric hybridization involving Tsuga heterophylla and Picea sitchensis. Chromatographic data derived from extensive sampling in the western Cascades of Washington led me to conclude that hybridization of Tsuga heterophylla and T. mertensiana is a possible but rare phenomenon and is not necessarily indicated by morphological intermediacy. Phylogenetically both of these species are typical representatives of Tsuga and are distinct from species of Picea. There is, however, some support for the derivation of Tsuga mertensiana by intergeneric hybridization.     

Genetic analysis of hybrid seed formation ability of Brassica rapa in intergeneric crossings with Raphanus sativus

A hybridization barrier leads to the inability of seed formation after intergeneric crossings between Brassica rapa and Raphanus sativus. Most B. rapa lines cannot set intergeneric hybrid seeds because of embryo breakdown, but a B. rapa line obtained from turnip cultivar ‘Shogoin-kabu’ is able to produce a large number of hybrid seeds as a maternal parent by crossings with R. sativus. In ‘Shogoin-kabu’ crossed with R. sativus, developments of embryos and endosperms were slower than those in intraspecific crossings, but some of them grew to mature seeds without embryo breakdown. Intergeneric hybrid seeds were obtained in a ‘Shogoin-kabu’ line at a rate of 0.13 per pollinated flower, while no hybrid seeds were obtained in a line developed from Chinese cabbage cultivar ‘Chiifu’. F₁ hybrid plants between the lines of ‘Shogoin-kabu’ and ‘Chiifu’ set a larger number of hybrid seeds per flower, 0.68, than both the parental lines. Quantitative trait loci (QTLs) for hybrid seed formation were analyzed after intergeneric crossings using two different F₂ populations derived from the F₁ hybrids, and three QTLs with significant logarithm of odds scores were detected. Among them, two QTLs, i.e., one in linkage group A10 and the other in linkage group A01, were detected in both the F₂ populations. These two QTLs had contrary effects on the number of hybrid seeds. Epistatic interaction between these two QTLs was revealed. Possible candidate genes controlling hybrid seed formation ability in QTL regions were inferred using the published B. rapa genome sequences.     

Genome structure and apomixis in Phoenicaulis (Brassicaceae; Boechereae)

Apomixis in crucifer (Brassicaceae) species is rare, reported in just four genera (Boechera, Draba, Erysimum, and Parrya), and one intergeneric hybrid (Raphanobrassica). It is well studied only in Boechera, where it is widespread among 100+ recognized species. However, its occurrence in related genera of the tribe Boechereae has not been documented previously. Here we analyzed genome evolution, mode of reproduction, and fertility of the monospecific Boechereae genus Phoenicaulis (P. cheiranthoides), endemic to the northwestern United States. We discovered that the species encompasses diploid (2n = 2x = 14), triploid (2n = 3x = 21), and tetraploid (2n = 4x = 28) populations. Comparative chromosome painting analyses revealed that the three karyotypes are essentially structurally identical, differing only in the presence of a largely heterochromatic chromosome (Het) in the triploid and tetraploid cytotypes. The genome structure of Phoenicaulis appeared identical to that of Boechera species previously analyzed, suggesting genomic stasis despite the morphological and molecular divergence of the two genera. This genome colinearity extended to the presence and structure of the Het chromosomes, which are closely associated with apomictic reproduction in Boechera. Interestingly, all three cytotypes of Phoenicaulis proved to be apomictic, regardless of the presence or absence of a Het chromosome, and sexual populations have yet to be identified.     

Interspecific hybridization in Rorippa (Brassicaceae): Patterns and processes

The current knowledge on natural hybridization between European lowland Rorippa species is reviewed. Morphological, cytological and molecular markers provide substantial evidence that four Rorippa species (R. amphibia, R. austriaca, R. palustris and R. sylvestris) are involved in hybridization processes. The main factors promoting initial hybridization events between Rorippa species in Europe are (1) natural and anthropogenic habitat disturbance, (2) the invasion of non‐native R. austriaca into western central Europe and (3) the self‐incompatibility system of R. amphibia, R. austriaca and R. sylvestris coupled with clonal growth. Outcomes of hybridization between European Rorippa species show a broad range from incidental hybrids through the formation of hybrid swarms to the evolution of new hybrid taxa. Rorippa × armoracioides is certainly the most successful Rorippa hybrid. It results from hybridization between R. austriaca and R. sylvestris and is known from many localities in the native range of R. austriaca and in regions invaded by R. austriaca. Within this system hybrid zones of different age provide the rare opportunity to analyse different stages of hybrid formation and hybrid speciation in natural populations.     

Nuclear crystals, lampbrush-chromosome-like structures, and perinuclear cytoskeletal elements associated with nuclear fragmentation in characean internodal cells

Summary This article gives a survey of nucleus-associated structures and inclusions in a diverse range of characean algae includingChara braunii Gm.,Chara corallina Klein ex Willd., em. R.D.W.,Nitella cristata A.Br., em. R.D.W.,Nitella flexilis (L.) Ag.,Nitella furcata (Roxb. ex Bruz.) Ag. em. R.D.W.,Nitella hyalina (DC.) Ag.,Nitella pseudoflabellata A.Br., em. R.D.W.,Nitella pseudoflabellata var.imperialis T.F.A.,Nitella translucens var.axillaris (A.Br.) R.D.W. andNitellopsis obtusa (Desv. in Lois.) J.Gr. Lampbrushchromosome-like structures were found in nuclei ofNitella flexilis andNitellopsis obtusa and seem to be involved in the distribution of genetic material during nuclear fragmentation. Intranuclear tubular crystals of unknown protein composition were present in all species, especially in young, elongating cells, and could be important for establishing the main axis of the nuclei. Spindle-shaped protein crystals that originate in the nucleus and are released into the cytoplasm upon nuclear degeneration were observed in branchlet internodal cells of one population ofNitella flexilis. Perinuclear microtubules were present in all species, but perinuclear actin fibrils were hitherto only found in mostNitella species and inNitellopsis obtusa. None of these nucleus-associated structures seems to be responsible for the formation of constrictions leading to nuclear fragmentation. These constrictions were perpendicular to the main axis of the nucleus and symmetrical in theNitella species but asymmetric inC. braunii, C. corallina, and inNitellopsis obtusa. Statistical analysis of nuclear size, number and constriction sites indicate that fragmentation is a nonsynchronous process independent of the light-dark cycle.Abbreviations CLSM confocal laser scanning microscopy - DAPI 4,6-diamidino-2-phenylindole - DIC Nomarski differential interference contrast - LCLS lampbrush chromosome-like structure(s) Dedicated to Professor Walter Gustav Url on the occasion of his 70th birthday     

Observations on pollination inSarcostemma (Asclepiadaceae)

Field observations on pollination in New World species of the genusSarcostemma R. Br. sensuHolm are reported. Morphological and anatomical comparisons of pollinated flowers ofSarcostemma subg.Ceramanthus Kuntze (New World) andSarcostemma subg.Sarcostemma (Old World) are presented.