Molecular genetics of growth and development in Populus (Salicaceae). v. mapping quantitative trait loci affecting leaf variation

We examined the genetic variation of leaf morphology and development in the 2-yr-old replicated plantation of an interspecific hybrid pedigree of Populus trichocarpa T. & G. and P. deltoides Marsh. via both molecular and quantitative genetic methods. Leaf traits chosen were those that show pronounced differences between the original parents, including leaf size, shape, orientation, color, structure, petiole size, and petiole cross section. Leaves were sampled from the current terminal, proleptic, and sylleptic branches. In the F2 generation, leaf traits were all significantly different among genotypes, but with significant effects due to genotype X crown-position interaction. Variation in leaf pigmentation, petiole length. And petiole length proportion appeared to be under the control of few quantitative trait loci (QTLs). More QTLs were associated with single leaf area, leaf shape, lamina angle, abaxial color, and petiole flatness, and in these traits the number of QTLs varied among crown positions. In general, the estimates of QTL numbers from Wright's biometric method were close to those derived from molecular markers. For those traits with few underlying QTLs, a single marker interval could explain from 30 to 60% of the observed phenotypic variance. For multigenic traits, certain markers contributed more substantially to the observed variation than others. Genetic cluster analysis showed developmentally related traits to be more strongly associated with each other than with unrelated traits. This finding was also supported by the QTL mapping. For example, the same chromosomal segment of linkage group L seemed to account for 20% of the phenotypic variation of all dimension-related traits, leaf size, petiole length. and midrib angle. In both traits. the P. deltoides alleles had positive effects and were dominant to the P. trichocarpa alleles. Similar relationships were also found for lamina angle. abaxial greenness, and petiole.     

Molecular Genetics of Growth and Development in Populus. IV. Mapping Qtls with Large Effects on Growth, Form, and Phenology Traits in a Forest Tree

We have mapped quantitative trait loci (QTLs) for commercially important traits (stem growth and form) and an adaptive trait (spring leaf flush) in a Populus F(2) generation derived from a cross between interspecific F(1) hybrids (P. trichocarpa X P. deltoides). Phenotypic data were collected over a 2-year period from a replicated clonal trial containing ramets of the parental, F(1), and F(2) trees. Contrary to the assumptions of simple polygenic models of quantitative trait inheritance, 1-5 QTLs of large effect are responsible for a large portion of the genetic variance in each of the traits measured. For example, 44.7% of the genetic variance in stem volume after 2 years of growth is controlled by just two QTLs. QTLs governing stem basal area were found clustered with QTLs for sylleptic branch leaf area, sharing similar chromosomal position and mode of action and suggesting a pleiotropic effect of QTLs ultimately responsible for stem diameter growth.     

百合‘Siberia’בManissa’种间杂交后代的染色体核型分析

以东方百合杂种系(Oriental hybrids group)品种‘Siberia’为母本,OT杂种系(interspecific hybrids betweenOriental and Longiflorum/OT group)品种‘Manissa’为父本杂交获得种间杂交F1代,对亲本及F1代株系的染色体数目和形态特征进行了分析。结果显示,母本东方百合‘Siberia’为二倍体即24条染色体,而父本‘Manissa’是高度杂合后代,为三倍体即36条染色体。杂交F1代的8个株系中有6个株系为二倍体即24条染色体,有2个株系为非整倍体,染色体条数分别为25和26条。母本‘Siberia’的核型为4m(1SAT)+10st(1SAT)+10t,父本‘Manis-sa’的核型为3m+18st(1SAT)+15t(1SAT),均属3B型。杂种F1代核型出现了多种类型,其中株系a、b、h为3B型,株系c、d、e、f为3A型,株系g为4B型。与亲本染色体形态相比,F1代株系出现了随体及端部着丝点染色体较多等染色体形态结构特征,而亲本没有这些特征。从染色体的形态、随体来看,子代为真杂种,在遗传上均偏向于母本。     

Genetic architecture of qualitative and quantitative Melampsora larici-populina leaf rust resistance in hybrid poplar: genetic mapping and QTL detection

In order to elucidate the genetic control of resistance to Melampsora larici-populina leaf rust in hybrid poplars, a Populus deltoides x P. trichocarpa F(1) progeny was analysed for qualitative and quantitative rust resistances. This progeny was evaluated for three components of quantitative resistance (latent period, uredinia number and uredinia size) to seven M. larici-populina strains in controlled conditions, and for one component of field susceptibility (rust colonization on the most infected leaf). One qualitative resistance locus inherited from P. deltoides, R(1), was localized on the genetic map. It segregates 1 : 1 in the F(1) progeny and is effective against four of the studied strains. QTL analysis was performed separately on R(1) and r(1) genotype subsets. An additional detection was conducted on the entire F(1) progeny for the three strains able to overcome R(1) and for MAX2. A total of nine QTLs were detected. Two had large, broad-spectrum effects. One (R(US)) is inherited from the P. trichocarpa parent; the other is inherited from P. deltoides and colocalized with R(1). Seven QTLs had only limited and specific effects. Significant interaction effects were detected mainly between the two major QTLs. Implications of these results for durable resistance breeding strategies, and possible benefits from the Populus genome sequence, are discussed.     

Dense genetic linkage maps of three Populus species (Populus deltoides, P. nigra and P. trichocarpa) based on AFLP and microsatellite markers

Populus deltoides, P. nigra, and P. trichocarpa are the most important species for poplar breeding programs worldwide. In addition, Populus has become a model for fundamental research on trees. Linkage maps were constructed for these three species by analyzing progeny of two controlled crosses sharing the same female parent, Populus deltoides cv. S9-2 x P. nigra cv. Ghoy and P. deltoides cv. S9-2 x P. trichocarpa cv. V24. The two-way pseudotestcross mapping strategy was used to construct the maps. Amplified fragment length polymorphism (AFLP) markers that segregated 1:1 were used to form the four parental maps. Microsatellites and sequence-tagged sites were used to align homoeologous groups between the maps and to merge linkage groups within the individual maps. Linkage analysis and alignment of the homoeologous groups resulted in 566 markers distributed over 19 groups for P. deltoides covering 86% of the genome, 339 markers distributed over 19 groups for P. trichocarpa covering 73%, and 369 markers distributed over 28 groups for P. nigra covering 61%. Several tests for randomness showed that the AFLP markers were randomly distributed over the genome.     

Differential susceptibility of poplar hybrids to the aphid Chaitophorus leucomelas (Homoptera: Aphididae)

After its recent introduction to Chile, the aphid Chaitophorus leucomelas Koch is becoming a serious pest affecting commercial poplar, Populus spp., plantations. The pattern of natural infestation of C. leucomelas among poplar hybrids with different pedigrees and the aphid intrinsic rate of increase (r(m)), of C. leucomelas were assessed in the field. In most of the hybrids, aphid abundance peaked in March (late summer). Among 12 types of poplar crosses, [(P. trichocarpa Torr. & Gray x P. deltoides Bartram ex Marshall) x (P. trichocarpa x P. deltoides)] and [(P. trichocarpa x P. maximowiczii Henry) x P. maximowiczii] showed the highest and lowest aphid densities, respectively. A trend to find more aphids in branch bases was apparent. The intrinsic rate of C. leucomelas increase was higher in [(P. trichocarpa x P. deltoides) x P. deltoides] hybrids, and lower in [(P. trichocarpa x P. maximowiczii) x P. trichocarpa] hybrids. Aphid density and performance were higher in hybrids with P. deltoides parentage, whereas hybrids with P. maximowiczii parentage showed lower aphid densities and performance. Hybrids with P. nigra L. parentage, namely, [P. trichocarpa x P. nigra], also had high aphid density, but aphid performance was lower compared with hybrids with P. deltoides parentage. These results suggest that among poplar hybrids studied, susceptibility to C. leucomelas is inherited through P. deltoides, whereas resistance seems to be inherited through P. maximowiczii. Thus, P. maximowiczii hybrids are recommended for commercial or ornamental planting programs in zones where there is a high risk of aphid infestation.     

Cytological mechanisms of gynogenesis and sperm incorporation in unreduced diploid eggs of the clonal loach, Misgurnus anguillicaudatus (Teleostei: Cobitidae)

The loach Misgurnus anguillicaudatus comprises diploid clonal, triploid and diploid-triploid mosaic individuals in a wild population on Hokkaido island, Japan. When diploid eggs of clonal loaches are fertilized by haploid sperm of normal bisexual loaches, both diploid clonal and non-diploid aclonal individuals occur in the progeny. Flow cytometry and microsatellite analyses revealed that the occurrence of triploid, diploid-triploid and other progeny was essentially due to the genetic incorporation of sperm to diploid clonal genomes of unreduced eggs. In this study, we examined the influence of water temperature from fertilization to early embryogenesis on frequencies of diploid clonal and other progeny and observed that progeny of three out of four clonal females examined exhibited approximately constant rates of diploid clonal individuals (54.2-68.9%) at hatching stage. Thus, no drastic increase of non-diploid progeny was detected. However, the 28 degrees C group of the fourth clonal female gave significantly lower rate (28.1%) of diploid clonal progeny, suggesting that this temperature might be a critical or a borderline temperature inducing sperm incorporation. We also examined the cytological process by which diploid clonal and other aclonal progeny develop after fertilization. In some fertilized eggs, the sperm nucleus remained condensed throughout fertilization and early embryogenesis and never fused with the female pronucleus. This cytological observation concludes that clonal eggs develop by the mechanism of gynogenesis. However, some other eggs showed the cytological process of syngamy between the female pronucleus and an accidentally formed male nucleus, suggesting the formation of triploid progeny. The syngamy between an accidentally activated sperm nucleus with a male pronucleus-like structure and nucleus of a blastomere of gynogenetically developing clonal diploid embryo might produce a diploid-triploid mosaic individual.     

Chromosome set manipulations and hybridization experiments in gilthead seabream (Sparus aurata). II. Assessment of diploid and triploid hybrids between gilthead seabream and red seabream (Pagrus major)

The experiments were designed to evaluate the suitability for mariculture of the diploid and triploid hybrids of gilthead seabream Sparus aurata and red seabream Pagrus major , both of which are members of the Sparidae family. Performance testing of the hybrids was carried out in comparison with the parental species under the same controlled environment. The reciprocal diploid hybrids as well as the triploid hybrid did not exhibit any significant growth advantage over diploid parental species either before or after sexual maturity. The adults, both reciprocal diploid hybrids and triploid hybrid (female S. aurata × male P. major ), were clearly immature and had only vestigial gonads; neither ovaries nor released milts were observed. Histological examination of the gonads, carried out during associated periods of the first and second maturation cycles of the parental species, showed that all the hybrids were completely sterile. Despite their sterility, the growth of the hybrids did not display any positive effect, and for this reason their commercial culture appears to be questionable. On the other hand, the use of sterilization through hybridization and chromosome set manipulation may be important when there is a need to restrict the ecological impact on a wild population.     

Clonal diploid sperm of the diploid-triploid mosaic loach, Misgurnus anguillicaudatus (Teleostei:Cobitidae)

The loach Misgurnus anguillicaudatus comprises diploid, triploid and diploid-triploid mosaic individuals in a wild population of the Hokkaido island, Japan. Previous studies revealed the presence of a cryptic clonal lineage among diploid loaches, which is maintained by uniparental reproduction of genetically identical diploid eggs. In the present study, we analyzed distribution and genetic status of diploid and triploid cells in infrequent mosaic males. Flow cytometry, microsatellite genotyping and DNA fingerprinting verified that mosaic males consisted of diploid cells with genotypes identical to the natural clone and triploid cells with diploid genomes of the clonal lineage plus haploid genome from sperm nucleus of the father. Thus, the occurrence of diploid-triploid mosaicism might be caused by accidental fertilization of a diploid blastomere nucleus with haploid sperm after the initiation of clonal development of unreduced eggs. Such mosaic males produced fertile sperm with diploid DNA content. The experimental cross between normal diploid female and diploid-triploid mosaic male gave rise to the appearance of triploid progeny which exhibited two microsatellite alleles identical to the clonal genotype and one allele derived from the normal female. In DNA fingerprinting, such triploid progeny gave not only all the DNA fragments from the clone, but also other fragments from the normal female. Induced androgenesis using UV irradiated eggs and sperm of the mosaic male gave rise to the occurrence of diploid individuals with paternally derived microsatellite genotypes and DNA fingerprints, absolutely identical to the natural clonal lineage. These results conclude that the diploid-triploid mosaic male produced unreduced diploid sperm with genetically identical genotypes. The spermatogenesis in the clonal diploid cells under the mosaic condition suggests that triploid male somatic cells might transform genetically all-female germ cells to differentiate into functionally male gametes. The discovery of the mosaic male producing unreduced sperm suggests the theoretical occurrence of triploids and other polyploids by the syngamy of such paternally derived diploid gametes.     

Gene introgression into Coffea arabica by way of triploid hybrids (C. arabica x C. canephora)

Interspecific triploid hybrid plants between the tetraploid species Coffea arabica L. and the diploid species C. canephora P. were backcrossed to C. arabica. Although characterised by a low production and an important fruit dropping, all attempted crosses (ie, 6) generated BC(1) progenies. Flow cytometric analysis of the nuclear DNA content revealed that most of the BC1 individuals were nearly tetraploid. Among the male gametes produced by the interspecific triploid hybrids, those presenting a high number of chromosomes appeared strongly favoured. Only pollen mother cells having nearly 22 chromosomes were effective, the others leading to deficient endosperm and fruit dropping. Molecular markers (ie, microsatellite and AFLP) combined with evaluations of morphological characteristics and resistance to leaf rust were applied to verify the occurrence of gene transfer from C. canephora into C. arabica, and to estimate the amount of introgression present in BC(1) individuals. The results reveal a strong deficiency in the C. canephroa alleles indicating a severe counter-selection against the introgression of genetic material from C. canephora into C. arabica by way of triploid hybrids. However, introgressants displaying desirable traits such as a high resistance to leaf rust were obtained. The low level of introgression could be an advantage by facilitating the recovery of the recurrent parent and possibly reducing the number of required backcrosses. On the other hand, this could be a limitation when attempting the transfer of a complex trait or several simply inherited traits.     

The formation of diploid and triploid hybrids of female grass carp × male blunt snout bream and their 5S rDNA analysis

Background

Hybridization is a useful strategy to alter the genotypes and phenotypes of the offspring. It could transfer the genome of one species to another through combing the different genome of parents in the hybrid offspring. And the offspring may exhibit advantages in growth rate, disease resistance, survival rate and appearance, which resulting from the combination of the beneficial traits from both parents.

Results

Diploid and triploid hybrids of female grass carp (Ctenopharyngodon idellus, GC, Cyprininae, 2n?=?48)?×?male blunt snout bream (Megalobrama amblycephala, BSB, Cultrinae, 2n?=?48) were successfully obtained by distant hybridization. Diploid hybrids had 48 chromosomes, with one set from GC and one set from BSB. Triploid hybrids possessed 72 chromosomes, with two sets from GC and one set from BSB.The morphological traits, growth rates, and feeding ecology of the parents and hybrid offspring were compared and analyzed. The two kinds of hybrid offspring exhibited significantly phenotypic divergence from GC and BSB. 2nGB hybrids showed similar growth rate compared to that of GC, and 3nGB hybrids significantly higher results. Furthermore, the feeding ecology of hybrid progeny was omnivorous.The 5S rDNA of GC, BSB and their hybrid offspring were also cloned and sequenced. There was only one type of 5S rDNA (designated type I: 180 bp) in GC and one type of 5S rDNA (designated type II: 188 bp) in BSB. However, in the hybrid progeny, diploid and triploid hybrids both inherited type I and type II from their parents, respectively. In addition, a chimera of type I and type II was observed in the genome of diploid and triploid hybrids, excepting a 10 bp of polyA insertion in type II sequence of the chimera of the diploid hybrids.

Conclusions

This is the first report of diploid and triploid hybrids being produced by crossing GC and BSB, which have the same chromosome number. The obtainment of two new hybrid offspring has significance in fish genetic breeding. The results illustrate the effect of hybridization and polyploidization on the organization and variation of 5S rDNA in hybrid offspring.

     

Phenotypic consequences of genetic variation in a gynogenetic complex of Phoxinus eos-neogaeus clonal fish (Pisces: Cyprinidae) inhabiting a heterogeneous environment

We examined the genetic composition, habitat use, and morphological variation of a Phoxinus eos-neogaeus unisexual hybrid complex and its sexually reproducing progenitor species inhabiting beaver-modified drainages of Voyageurs National Park, Minnesota. In addition to the single diploid P. eos-neogaeus gynogenetic clone, triploid and diploid-triploid mosaic biotypes were present at our study sites. Both P. eos and P. neogaeus, and all three hybrid biotypes were ubiquitous throughout one intensively surveyed drainage, but abundances and relative frequencies of the parental species and hybrids varied considerably within and among successional environments. Data from a large number of additional sites indicated that the proportion of polyploid hybrids within an environment was negatively related to hybrid relative frequency, implying that the genomic constitution of hybrids is an important determinant of clonal fitness among successional environments. Statistical comparisons of variation along size-free multivariate body shape axes indicated that despite its genetic uniformity, the P. eos-neogaeus clone is no less variable than its sexual progenitors, suggesting that a single genotype may actually respond to environmental variation with as much phenotypic variation as a genetically variable sexual population. The incorporation and expression of a third genome in triploid and diploid-triploid mosaic biotypes derived from the gynogenetic clone significantly expanded phenotypic variation of the clone. This additional variation results in greater similarities in habitat use and morphological overlap with the parental species, primarily P. eos, the predominant sperm donor for gynogenetic hybrid females in this complex. Polyploid augmentation of a diploid gynogenetic clone appears to be typical in the P. eos-neogaeus complex, and the additional genetic and phenotypic variation that it generates has potentially significant ecological and evolutionary consequences for the success and persistence of a single genotype in highly variable environments.     

Extensive citrus triploid hybrid production by 2x?×?4x sexual hybridizations and parent-effect on the length of the juvenile phase

The citrus fresh market demands the production of seedless citrus fruits, as seedy fruits are not accepted by consumers. The recovery of triploid plants has proven to be the most promising approach to achieve this goal, since triploids have very low fertility, are generally seedless and do not induce seeds in other cultivars by cross pollination. Triploid plants can be recovered by 2x?×?4x sexual hybridization. In this work, we present an effective methodology to recover triploid plants from 2x?×?4x hybridizations based on in vitro embryo rescue, ploidy level analysis by flow cytometry and genetic origin of triploid plants. The pollen viability of diploid and tetraploid citrus genotypes was analyzed by comparing the pollen germination rate in vitro. The pollen viability of tetraploid (doubled-diploid) genotypes is generally reduced but sufficient for successful pollination. Triploid embryos were identified in normal and undeveloped seeds that did not germinate under greenhouse conditions. The influence of parents and environmental conditions on obtaining triploid plants was analyzed and a strong interaction was noted between the parents and environmental conditions. The parental effect on the length of the juvenile phase was also demonstrated through observations of a large number of progeny over the last 15?years. The juvenile phase length of the triploid hybrids obtained with 'Fortune' mandarin as female parent and tetraploid 'Orlando' tangelo as male parent was shorter than the juvenile phase obtained with a clementine as female parent and tetraploids of 'Nova', 'W. Leaf' and 'Pineapple' male parents. Key message Effective methodology to recover citrus triploid plants from 2x?×?4x sexual hybridizations and the parental effect on the length of the juvenile phase.     

Comparative and Evolutionary Analysis of the Cytochrome b Sequences in Cyprinids with Different Ploidy Levels Derived from Crosses

The mitochondrial cyt b genes in the allotetraploid and triploid crucian carp as well as triploid common carp were isolated and completely sequenced. Their DNA sequences were compared with those derived from the cyt b genes of the red crucian carp, Japanese crucian carp, and common carp with MEGA 1.0 software. Phylogenetic analysis revealed the sister relationships between allotetraploid and diploid red crucian carp, between the triploid crucian carp and diploid Japanese crucian carp, and between triploid common carp and diploid common carp. Our results indicated the cyt b genes in the allotetraploid, triploid crucian carp, and triploid common carp were maternally inherited. Through maternal inheritance, the cyt b gene in the F11 tetraploid displayed extremely high similarity to that in the female parent red crucian carp after 11 generations (from F1 to F11 hybrids). Since the establishment of the new tetraploid stocks has great significance in analyzing evolutionary theory of vertebrate and in improving aquaculture industry, analysis of the cyt b gene and the elucidation of the variation of the cyt b gene DNA in different cyprinids prove that cyt b is a useful genetic marker to monitor the variations in the progeny of the crosses.     

Diplospory and Parthenogenesis in Sexual x Agamospermous (Apomictic ) Erigeron (Asteraceae) Hybrids

Segregation for asexual seed production was evaluated for 130 experimental F1 hybrids resulting from a cross between diploid (2n=18) sexual Erigeron strigosus and triploid (2n=27) agamospermous Erigeron annuus. Paternity of hybrids was documented using 13 RAPD markers. The distribution of F1 chromosome numbers is bimodal, centering on diploid and triploid ploidal levels but with underrepresentation of diploids. Diplosporous versus meiotic megagametophyte development was ascertained microscopically for >/=100 ovules per plant. Diplospory ranges from 0% to 100% among all progeny but is uniformly low (0%-3%) for 17 diploid hybrids. The inheritance of diplospory in Erigeron appears to be best explained by a one-locus-two-allele polysomic model with selection against gametes homozygous for diplospory. Parthenogenesis, estimated via seed counts, ranges from 0% to 60% and apparently is contingent upon diplospory, as seed production was absent or very low in predominantly meiotic hybrids. However, the absence of parthenogenesis in many highly diplosporous hybrids indicates that these two aspects of agamospermous development are not strictly associated. The segregation of both diplospory and parthenogenesis in this population will permit further genetic dissection of these traits with molecular marker-based analyses.     

Fertility of triploid hybrids of Prussian carp (<Emphasis Type="Italic">Carassius gibelio</Emphasis>) with common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.)

Fertility of backcross triploid hybrids containing one genome of Prussian carp and two genomes of common carp is investigated. The females of hybrids of Prussian carp and common carp (Prussian × common carp) are prolific and produce diploid gametes. Since males of such hybrids are sterile, their reproduction is realized by means of induced gynogenesis. Triploid progeny is obtained by backcrossing female Prussian × common carp with carp males. Among triploids obtained from hybrids F₁ and among hybrids of the first gynogenetic generation, there were no prolific specimens. However, in reproduction of diploid hybrids by means of gynogenesis during six generations, the female fertility in the backcross progeny is restored. From backcross triploid females (daughters of Prussian × common carp of the sixth gynogenetic generation), a viable triploid gynogenetic progeny and a tetraploid backcross (by carp) progeny are obtained. The obtained data may be considered as the experimental proof of the hypothesis of reticular speciation.     

从ATPase8-6基因研究杂交多倍体鱼线粒体母性遗传

异源四倍体鲫鲤是世界上首例人工培育的两性可育并形成群体的且能自然繁殖的四倍体鱼。本文采用质粒克隆测序法测定了红鲫、异源四倍体鲫鲤、三倍体湘云鲫和三倍体湘云鲤的ATPase8和ATPase6基因全序列 ,结合鲤鱼、日本白鲫和斑马鱼的同源序列 ,对不同倍性水平鲤科鱼类的ATPase8和ATPase6基因进行了比较 ,分析了碱基组成、变异情况以及核苷酸和氨基酸序列差异。红鲫、鲤鱼、异源四倍体鲫鲤、日本白鲫、三倍体湘云鲫和三倍体湘云鲤之间的序列差异为 0 0 % - 1 3 4 % ,它们与外群斑马鱼之间的序列差异为 2 7 9% -31 0 %。用MEGA软件中的MP法、ME法、NJ法和UPGMA法构建分子系统树 ,得到了相似的拓扑结构。结果分析表明 ,人工杂交多倍体异源四倍体鲫鲤、三倍体湘云鲫和三倍体湘云鲤在线粒体ATPase8和ATPase6基因上具有严格的母性遗传特征。值得注意的是 ,异源四倍体鲫鲤经过 1 1代的繁育后 ,与其原始母本红鲫仍然保持了非常高的同源性 ,说明了新的异源四倍体基因库在线粒体ATPase8和ATPase6基因上拥有稳定的遗传特性。对不同倍性鲤科鱼类线粒体ATPase8和ATPase6基因的研究表明 ,ATPase8和ATPase6基因是杂交鱼后代遗传变异研究的一个很好的分子标记     

Quantitative trait loci and candidate gene mapping of bud set and bud flush in populus

The genetic control of bud phenology in hybrid poplar was studied by mapping quantitative trait loci (QTL) affecting the timing of autumn bud set and spring bud flush. The founders of the mapping pedigree were collected from widely separated latitudes to maximize segregating variation for dormancy-related traits in the F(2) generation-the female Populus trichocarpa parent is from Washington State (48 degrees N) and the male P. deltoides parent is from Texas (31 degrees N). Bud set and bud flush timing were measured on the F(2) generation in a replicated clonal field trial. Using a linkage map constructed of AFLP and microsatellite markers, three QTL controlling bud set and six QTL controlling bud flush were detected. Additionally, five candidate genes believed to be involved in perception of photoperiod (PHYB1, PHYB2) or transduction of abscisic acid response signals (ABI1B, ABI1D, and ABI3) were placed on the QTL map. PHYB2 and ABI1B were found to be coincident with QTL affecting bud set and bud flush.     

Organization and variation analysis of 5S rDNA in different ploidy-level hybrids of red crucian carp × topmouth culter

Through distant crossing, diploid, triploid and tetraploid hybrids of red crucian carp (Carassius auratus red var., RCC♀, Cyprininae, 2n = 100) × topmouth culter (Erythroculter ilishaeformis Bleeker, TC♂, Cultrinae, 2n = 48) were successfully produced. Diploid hybrids possessed 74 chromosomes with one set from RCC and one set from TC; triploid hybrids harbored 124 chromosomes with two sets from RCC and one set from TC; tetraploid hybrids had 148 chromosomes with two sets from RCC and two sets from TC. The 5S rDNA of the three different ploidy-level hybrids and their parents were sequenced and analyzed. There were three monomeric 5S rDNA classes (designated class I: 203 bp; class II: 340 bp; and class III: 477 bp) in RCC and two monomeric 5S rDNA classes (designated class IV: 188 bp, and class V: 286 bp) in TC. In the hybrid offspring, diploid hybrids inherited three 5S rDNA classes from their female parent (RCC) and only class IV from their male parent (TC). Triploid hybrids inherited class II and class III from their female parent (RCC) and class IV from their male parent (TC). Tetraploid hybrids gained class II and class III from their female parent (RCC), and generated a new 5S rDNA sequence (designated class I-N). The specific paternal 5S rDNA sequence of class V was not found in the hybrid offspring. Sequence analysis of 5S rDNA revealed the influence of hybridization and polyploidization on the organization and variation of 5S rDNA in fish. This is the first report on the coexistence in vertebrates of viable diploid, triploid and tetraploid hybrids produced by crossing parents with different chromosome numbers, and these new hybrids are novel specimens for studying the genomic variation in the first generation of interspecific hybrids, which has significance for evolution and fish genetics.     

Identification of QTLs affecting adaptive traits in Castanea sativa Mill

A QTL analysis for three different adaptive traits was performed in an F₁ progeny of Castanea sativa Mill. The female and male parents originated from two Turkish chestnut populations adapted to a drought and humid environment, respectively. QTLs for bud flush, growth and carbon isotope discrimination were detected over a 3‐year period. Bud set was also recorded in the last year of measurement. Thirty‐five individual QTLs were detected for phenology, 28 for growth and 17 for carbon isotope discrimination, most of them explaining a low to moderate proportion of the total phenotypic variance. QTLs were distributed throughout the whole genome. Temporally stable QTLs were identified for all the traits analysed, with phenology showing the higher proportion of stable QTLs. Interesting phenotypic correlations and co‐localizations among QTLs for different adaptive traits were observed, allowing the formulation of an hypothesis about the genetic adaptation of the female parent to drought.