The origin of natural tetraploid loach Misgurnus anguillicaudatus (Teleostei: Cobitidae) inferred from meiotic chromosome configurations

In the loach, or Oriental weatherfish Misgurnus anguillicaudatus (Teleostei: Cobitidae), diploid (2n = 50) and tetraploid individuals (4n = 100) are often sympatric in central China. The evolutionary mechanism of this tetraploidization was analyzed with the observation of meiotic behavior of chromosomes in both the germinal vesicles of mature oocytes and the primary spermatocytes in diploid and tetraploid loaches. Whereas diploid specimens usually showed 25 bivalents in meiotic cells, tetraploid loaches exhibited 0-6 quadrivalents and 38-50 bivalents in both sexes, with the modal number of quadrivalents as three in females and four in males. In the diploid specimens, the two largest metacentric chromosomes bearing nucleolar organizing regions (NORs) identified by chromomycin A(3) staining and fluorescence in situ hybridization with a 5.8S + 28S rDNA probe formed one bivalent with terminal association. In the tetraploids, four NOR-bearing chromosomes never formed a quadrivalent, but were organized into two terminally-associated bivalents. These findings suggest an autotetraploid origin of the natural tetraploid loach and subsequent rediploidization of whole genome. The latter process, however, seems still in progress as inferred from the concurrence of up-to several quadrivalents and the majority of bivalents.     

The Hyparrhenia involucrata—H. subplumosa (Gramineae) complex in Nigeria: morphological and cytological characterization

Hyparrhenia involucrata Stapf is an annual with diploid, aneuploíd, tetraploid and hexaploid chromosome races on a base of x = 10, whilst M. subplumosa Stapf is known to be tetraploid and perennial. The two species overlap considerably in their vegetative and floral attributes. Whilst the floral characteristics (such as number of awns and sex of imperfect flowers) are fairly constant within H. involucrata , they are quite variable in H. subplumosa : the evolutionary significance of some of these variations is discussed. Some of the observations on size, variability and fertility of pollen grains are interpreted using data from chromosome numbers and meiotic behaviour. Preliminary observations on the hybrids between a diploid race of H. involucrata and H. subplumosa indicate that the genomes of the two species are highly homologous and that perennial habit is a dominant trait controlled by a single gene.     

Taxonomic and evolutionary implications of intraspecific variability in chromosome numbers of species of Leucaena Benth. (Leguminosae)

Chromosome numbers were determined in 52 individuals of 14 taxa of Leucaena Benth. from 22 populations. For L. cuspidata and L. kmpirana these are the first published chromosome counts. Intraspecific variability was found for L. lempirana, L. macrophjlta and L. shanonii , and one diploid population of the tetraploid species L. pallida was identified. Comparison of our data with those in the literature showed that for L. collinsii and L. macrophylla there is a relationship between chromosome number and subspecies delimitation. The variability detected in chromosome numbers shows the complexity of the diploid and tetraploid species evolution, and suggests multiple origins for some of the polyploid taxa.     

TAXONOMIC SIGNIFICANCE OF CHROMOSOME OBSERVATIONS IN CARIBBEAN SPECIES OF LANTANA (VERBENACEAE)

Chromosome numbers and, in most cases, meiotic configurations are provided for 12 taxa and 5 morphological intermediates of Lantana collected in the Bahamas, Dominican Republic, Florida, the Lesser Antilles, Puerto Rico, and Texas. Reported for the first time are Lantana bahamensis, n = 11; L. microcephala, n = 12; L. leonardiorum, n = 11; L. odorata, n = 12; L. reticulata, n = 24; L. subcordata, n = 11; L. urticifolia, n = 11, 22. Numbers differing from previous reports were obtained for L. involucrata, n = 12, 24, and L. trifolia, n = 27. Triploids indicate the natural occurrence of hybridization between diploid and tetraploid taxa. Bivalents are formed regularly, except in the triploids and in morphologically intermediate tetraploids. These reports confirm that Lantana is based on at least two numbers, x = 11 and 12, and that the genus comprises polyploid complexes in each of these basic lines. The polyploids are weedier and more widely distributed than are the diploids. Chromosome numbers and configurations aid in the delimitation of diploid foundation species and in the recognition of naturalized hybrids.     

Cytological analysis of tetraploid hybrids between sweet potato and diploid Ipomoea trifida (H. B. K.) Don.

Summary Tetraploid F₁ hybrids between Ipomoea batatas, sweet potato (2n = 6x = ca. 90), and diploid (2n = 2x = 30) I. trifida (H. B. K.) Don. showed various degrees of fertility reduction. The present study aimed to clarify its causes by cytological analysis of meiotic chromosome behavior in the diploid and sweet potato parents and their tetraploid hybrids. The diploid parents showed exclusively 15 bivalents, and the sweet potato parents exhibited almost perfect chromosome pairing along with predominant multivalent formation. Their hybrids (2n = 4x= 57–63) formed 2.6–5.0 quadrivalents per cell, supporting the autotetraploid nature. The meiotic aberratios of the hybrids were characterized by the formation of univalents, micronuclei, and abnormal sporads (monad, dyad, triad, and polyad). The causes underlying these aberrations were attributed in part to the multivalent formation, and in part to a disturbance in the spindle function. Three hybrids showing serious meiotic aberrations were very low in fertility. The utilization of the sweet potato-diploid I. trifida hybrids for sweet potato improvement is described and, further, the role of interploidy hybridization in the study of the sweet potato evolution is discussed.     

Microsporogenesis in Brachiaria dictyoneura (Fig. & De Not.) Stapf (Poaceae: Paniceae)

Microsporogenesis was analyzed in five accessions of Brachiaria dictyoneura presenting x = 6 as the basic chromosome number. All accessions were tetraploid (2n = 4x = 24) with chromosome pairing in bi-, tri-, and quadrivalents. The recorded meiotic abnormalities were those typical of polyploids, including precocious chromosome migration to the poles, laggard chromosomes, and micronucleus formation. The frequency of these abnormalities, however, was lower than those reported for other polyploid accessions previously analyzed for other Brachiaria species. Cell fusion and absence of cytokinesis were also recorded in some accessions, leading to restitutional nucleus formation in some cells. Genetically unbalanced microspores, binucleate, and 2n microspores were found among normal meiotic products as results from these abnormalities. The limitation in using these accessions as pollen donor in interspecific crosses with sexual species with x = 7 or x = 9 in breeding programs is discussed.     

A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

中国姜花属十九个分类群的细胞学研究

采用压片法对中国姜花属十八个分类群进行了体细胞染色体计数,对白姜花减数分裂终变期I的染色体数目和形态进行了观察。结果显示:包括白姜花在内的十九个分类群中有六个二倍体,一个三倍体,十二个四倍体,其中十二个分类群的体染色体数目为首次报道,显示中国姜花属植物具有较高比例的多倍体类型;姜花属的染色体基数为n=17,染色体组可能是多倍体起源的。     

Polyploidy in an Amphimictic Population of Heterodera glycines

A tetraploid single-cyst isolate of Heterodera glycines from a field population from Indiana has been propagated in the greenhouse on Lee soybeans since its discovery, in 1973. The tetraploid isolate has n = 18 chromosomes, compared with n = 9 of the diploid H. glycines; it has larger cysts and larvae, but shows the same level of parasitism and host range as the diploid population from which it apparently evolved. Association of chromosomes is irregular at metaphase I, with quadrivalents, trivalents, and univalents often observed in addition to the bivalents. The second maturation division is usually normal. About 80% of the mature oocytes (just before fertilization) have n = 18, and the other 20% have n = 17 or 19. Reproduction of the tetraploid isolate is exclusively by cross-fertilization. The discovery of such a tetraploid provides an experimental tool for the study of polyploidy in nematodes. Many amphimictic plant-parasitic nematodes are suspected of representing polyploids.     

Taxonomic relationships among Arachis sect. Arachis species as revealed by AFLP markers.

Cultivated peanut, Arachis hypogaea L., is a tetraploid (2n = 4x = 40) species thought to be of allopolyploid origin. Its closest relatives are the diploid (2n = 2x = 20) annual and perennial species included with it in Arachis sect. Arachis. Species in section Arachis represent an important source of novel alleles for improvement of cultivated peanut. A better understanding of the level of speciation and taxonomic relationships between taxa within section Arachis is a prerequisite to the effective use of this secondary gene pool in peanut breeding programs. The AFLP technique was used to determine intra- and interspecific relationships among and within 108 accessions of 26 species of this section. A total of 1328 fragments were generated with 8 primer combinations. From those, 239 bands ranging in size from 65 to 760 bp were scored as binary data. Genetic distances among accessions ranged from 0 to 0.50. Average distances among diploid species (0.30) were much higher than that detected between tetraploid species (0.05). Cluster analysis using different methods and principal component analysis were performed. The resulting grouping of accessions and species supports previous taxonomic classifications and genome designations. Based on genetic distances and cluster analysis, A-genome accessions KG 30029 (Arachis helodes) and KSSc 36009 (Arachis simpsonii) and B-genome accession KGBSPSc 30076 (A. ipaensis) were the most closely related to both Arachis hypogaea and Arachis monticola. This finding suggests their involvement in the evolution of the tetraploid peanut species.     

Chromosome counts in the genus Festuca section Eskia (Poaceae) in the Iberian Peninsula

Chromosome numbers of taxa of Festuca L. section Eskia Willk. in the Iberian Peninsula are given. The levels of ploidy for five taxa are confirmed. Idiograms and karyotypic formulae of the five taxa are presented for the first time. Two levels of ploidy occur in this section: diploid and tetraploid. One taxon, Festuca elegans ssp. merinoi is tetraploid and two other taxa have diploid and tetraploid populations. The remaining two taxa are solely diploid.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 331–337.     

Divergent and reticulate species relationships in Leucaena (Fabaceae) inferred from multiple data sources: insights into polyploid origins and nrDNA polymorphism

Previous analyses of species relationships and polyploid origins in the mimosoid legume genus Leucaena have used chloroplast DNA (cpDNA) restriction site data and morphology. Here we present an analysis of a new DNA sequence data set for the nuclear ribosomal DNA (nrDNA) 5.8S subunit and flanking ITS 1 and ITS 2 spacers, a simultaneous analysis of the morphology, ITS and cpDNA data sets for the diploid species, and a detailed comparison of the cpDNA and ITS gene trees, which include multiple accessions of all five tetraploid species. Significant new insights into species relationships and polyploid origins, including that of the economically important tropical forage tree L. leucocephala, are discussed. Heterogeneous ITS copy types, including 26 putative pseudogene sequences, were found within individuals of four of the five tetraploid and one diploid species. Potential pseudogenes were identified using two pairwise comparison approaches as well as a tree-based method that compares observed and expected proportions of total ITS variation contributed by the 5.8S subunit optimized onto branches of one of the ITS gene trees. Inclusion of putative pseudogene sequences in the analysis provided evidence that some pseudogenes in allopolyploid L. leucocephala are not the result of post-allopolyploidization gene silencing, but were inherited from its putative diploid maternal progenitor L. pulverulenta.     

Localized chiasmata and meiotic nodules in the tetraploid onion Allium porrum.

Allium porrum L. (cultivated leek) (2n = 4x = 32) is a fertile tetraploid that forms bivalents with pericentric chiasmata at metaphase I. To investigate the basis of this unusual behavior for a tetraploid, we describe the karyotype, axial cores, synaptonemal complexes (SCs), and meiotic nodules of A. porrum. The karyotype appears to be autotetraploid. This conclusion is also supported by presynaptic alignment of axial cores in groups of four and partner trades between pairs of SCs. Numerous early nodules are distributed all along axial cores and SCs during zygonema, but they are lost by late zygonema - early pachynema. Late (recombination) nodules (RNs) are present on SCs near kinetochores throughout the remainder of pachynema. This pattern of RNs corresponds to the pattern of pericentric chiasmata. Pachytene quadrivalents usually are resolved into bivalents because partner trades between SC lateral elements rarely occur between RNs on the same segment of SC. Thus, the patterns of crossing-over and partner trades promote balanced disjunction and high fertility in autotetraploid A. porrum. Rare quadrivalents observed at metaphase I must be due to infrequent partner trades between RNs. Polycomplexes, unusual in their number and size, were observed during zygonema. Key words : synaptonemal complex, recombination nodules, localized chiasmata, polycomplex, Allium porrum.     

Diversity and evolution of the Hordeum murinum polyploid complex in Algeria

Population diversity and evolutionary relationships in the Hordeum murinum L. polyploid complex were explored in contrasted bioclimatic conditions from Algeria. A multidisciplinary approach based on morphological, cytogenetic, and molecular data was conducted on a large population sampling. Distribution of diploids (subsp. glaucum) and tetraploids (subsp. leporinum) revealed a strong correlation with a North-South aridity gradient. Most cytotypes exhibit regular meiosis with variable irregularities in some tetraploid populations. Morphological analyses indicate no differentiation among taxa but high variability correlated with bioclimatic parameters. Two and three different nuclear sequences (gene coding for an unspliced genomic protein kinase domain) were isolated in tetraploid and hexaploid cytotypes, respectively, among which one was identical with that found in the diploid subsp. glaucum. The tetraploids (subsp. leporinum and subsp. murinum) do not exhibit additivity for 5S and 45S rDNA loci comparative with the number observed in the related diploid (subsp. glaucum). The subgenomes in the tetraploid taxa could not be differentiated using genomic in situ hybridization (GISH). Results support an allotetraploid origin for subsp. leporinum and subsp. murinum that derives from the diploid subsp. glaucum and another unidentified diploid parent. The hexaploid (subsp. leporinum) has an allohexaploid origin involving the two genomes present in the allotetraploids and another unidentified third diploid progenitor.     

Symbiotic Characteristics and Rhizobium Requirements of a Leucaena leucocephala x Leucaena diversifolia Hybrid and Its Parental Genotypes

In 56-day-old plants, Leucaena leucocephala and its hybrid with L. diversifolia showed 100% more total N than did L. diversifolia. Significant (P < 0.01) host-inoculation interaction in total N was 14.4% of the total phenotypic variation. The most effective and competitive Rhizobium sp. for the leucaenas was TAL 1145. Three-strain mixed inoculation was inferior to TAL 1145 alone.     

AUTOPOLYPLOIDY IN HEUCHERA MICRANTHA (SAXIFRAGACEAE)

Heuchera micrantha (Saxifragaceae) is a morphologically variable species comprising five varieties: diversifolia, erubescens, hartwegii, micrantha, and pacifica. Both diploids (2n = 14) and tetraploids (2n = 28) occur within the species. The tetraploid cytotype occupies the central portion of the geographic range of the species, whereas diploids occur primarily in the southern and northern portions of the range. Both diploids and tetraploids have been detected within vars. diversifolia, pacifica, and hartwegii. All counts for vars. erubescens and micrantha are diploid and tetraploid, respectively. Several lines of evidence suggest that tetraploid H. micrantha is of autopolyploid origin. The species is distinct morphologically and is also well separated geographically from other closely related species in subsection Micranthae. The two cytotypes are karyologically identical, possess nearly the same suite of allozymes, and have a very high genetic identity (Ī = 0.971). Significantly, an earlier study documented tetrasomic inheritance in the tetraploid cytotype. Following theoretical expectations, the mean number of alleles per locus, proportion of loci that are polymorphic, and observed heterozygosity are significantly higher for the autotetraploid than for the diploid. The occurrence of both cytotypes in three of the varieties suggests that autopolyploidy may have occurred several times independently in H. micrantha. This was further substantiated by discriminant analysis using morphological characters, which provided evidence for a minimum of two separate origins for the autopolyploid cytotype.     

Meiotic pairing in hybrids between tetraploid Triticale and related species: new elements concerning the chromosome constitution of tetraploid Triticale

Summary Two F5 strains of tetraploid triticale (2n= 4x=28), obtained from 6x triticaleX2 rye progenies, were crossed with diploid and tetraploid rye, some durum and bread wheats, and various 8x and 6x triticale lines. Meiosis in the different hybrid combinations was studied. The results showed that the haploid complement of these triticales consists of seven chromosomes from rye and seven chromosomes from wheat. High frequencies of PMCs showing trivalents were observed in hybrids involving the reference genotypes of wheat and triticale. These findings proved that several chromosomes from the wheat component have chromosome segments coming from two parental wheat chromosomes. The origin of these heterogeneous chromosomes probably lies in homoeologous pairing occurring at meiosis in the 6x triticaleX2x rye hybrids from which 4x triticale lines were isolated. A comparison among different hybrids combinations indicated that the involvement of D-genome chromosomes in homoeologous pairing is quite limited. In contrast, meiotic patterns in 4x triticale X 2x rye hybrids showed a quite high pairing frequency between some R chromosomes and their A and B homoeologues.     

Leucaena species valoration for biomass and paper production in 1 and 2 year harvest

In order to identify faster-growing non-woody species usable for biomass and paper production, four Leucaena species (L.diversifolia, L. colinsii, L. salvadorensis and three varieties of L. leucocephala) were tested. All the Leucaena species showed a good soil and climatic adaptation to Spain Southwest except for L. salvadorensis. Studied Leucaena species showed biomass productivity ranges from 67.14 to 9.44 t ha(-1) (o.d.b.) and 43.6 to 11.4 t ha(-1) under Mediterranean conditions for the first and second year sprouts, respectively. The quantity of solubles and extractives shows similar values when compared with wood materials. Relatively lower lignin content in Leucaena (from 15.7% to 21.4%) species has been found with respect to other vegetal species. The alpha-cellulose contents (39.4-45.3%) are in the range of the normal values expected for the other non-wood raw materials. The study confirms the feasibility of organocell yield pulping process to Leucaena species. Organocell process provides an efficient delignification (kappa number 12.4 and pulp yield 42.2%) for L. leucocephala and suitably physical characteristics of paper sheet (tensile index 20.3 kNm/kg for L. diversifolia).     

Chromosome behaviour and fertility of the raw and evolved synthetic tetraploids of pearl millet,Pennisetum typhoides stapf et hubb.

The effect of colchicine-induced chromosome doubling on phenotypic characters of Pearl millet,Pennisetum typhoides, is described and the mutagenic effect of colchicine preliminarily indicated.Meiosis in the raw tetraploids was characterized by a high frequency of multivalents, mostly quadrivalents. The evolutionary implication of the occurrence of multivalents higher than quadrivalents is discussed.When the synthetic autototraploids were carried through C₆, a shift from a multivalent to a bivalent type of association was noticed, and some of the quadrivalents formed in the C₅ and C₆ generations appeared to be loosely associated. It is suggested that structural divergence of the chromosomes combined with genetic factors may jointly be the cause. Evolutionary and breeding consequences are discussed. With the acquisition of a predominantly bivalent type of meiotic association, seed setting in the tetraploids improved. The relative roles of meiotic abnormalities and genetic factors in bringing about seed sterility in the tetraploids are considered.Cytological instability resulted in aneuploids and diploids in the progeny. Factors which may predispose a tetraploid taxon to cytological instability are discussed. It has been suggested that the secondarily diploid nature of Pearl millet may contribute to the cytological instability of its tetraploids.Preliminary observations on three trisomics and one monosomic, isolated in this study for the first time, are recorded. It was interesting to note that a monosomic plant of Pearl millet could survive up to maturity. This observation would further suggest that Pearl millet is not a true diploid but a secondarily balanced species with its phyletically basic number less thanx=7, as earlier inferred by the author from several evidences published elsewhere.