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Annchristin Ronnbergwastljung - One of the best experts on this subject based on the ideXlab platform.
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genome assembly of the basket willow Salix viminalis reveals earliest stages of sex chromosome expansion
BMC Biology, 2020Co-Authors: Pedro Almeida, Pascal Pucholt, Estelle Prouxwera, Allison M Churcher, Lucile Soler, Jacques Dainat, Jessica Nordlund, Tom Martin, Annchristin RonnbergwastljungAbstract:Sex chromosomes have evolved independently multiple times in eukaryotes and are therefore considered a prime example of convergent genome evolution. Sex chromosomes are known to emerge after recombination is halted between a homologous pair of chromosomes, and this leads to a range of non-adaptive modifications causing gradual degeneration and gene loss on the sex-limited chromosome. However, the proximal causes of recombination suppression and the pace at which degeneration subsequently occurs remain unclear. Here, we use long- and short-read single-molecule sequencing approaches to assemble and annotate a draft genome of the basket willow, Salix viminalis, a species with a female heterogametic system at the earliest stages of sex chromosome emergence. Our single-molecule approach allowed us to phase the emerging Z and W haplotypes in a female, and we detected very low levels of Z/W single-nucleotide divergence in the non-recombining region. Linked-read sequencing of the same female and an additional male (ZZ) revealed the presence of two evolutionary strata supported by both divergence between the Z and W haplotypes and by haplotype phylogenetic trees. Gene order is still largely conserved between the Z and W homologs, although the W-linked region contains genes involved in cytokinin signaling regulation that are not syntenic with the Z homolog. Furthermore, we find no support across multiple lines of evidence for inversions, which have long been assumed to halt recombination between the sex chromosomes. Our data suggest that selection against recombination is a more gradual process at the earliest stages of sex chromosome formation than would be expected from an inversion and may result instead from the accumulation of transposable elements. Our results present a cohesive understanding of the earliest genomic consequences of recombination suppression as well as valuable insights into the initial stages of sex chromosome formation and regulation of sex differentiation.
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genetic variation of biomass recalcitrance in a natural Salix viminalis l population
Biotechnology for Biofuels, 2019Co-Authors: Jonas A Ohlsson, Henrik R Hallingback, Mohamed Jebrane, Anne E Harmanware, Todd Shollenberger, Stephen R Decker, Mats Sandgren, Annchristin RonnbergwastljungAbstract:Salix spp. are high-productivity crops potentially used for lignocellulosic biofuels such as bioethanol. In general, pretreatment is needed to facilitate the enzymatic depolymerization process. Biomass resistance to degradation, i.e., biomass recalcitrance, is a trait which can be assessed by measuring the sugar released after combined pretreatment and enzymatic hydrolysis. We have examined genetic parameters of enzymatic sugar release and other traits related to biorefinery use in a population of 286 natural Salix viminalis clones. Furthermore, we have evaluated phenotypic and genetic correlations between these traits and performed a genomewide association mapping analysis using a set of 19,411 markers. Sugar release (glucose and xylose) after pretreatment and enzymatic saccharification proved highly variable with large genetic and phenotypic variations, and chip heritability estimates (h2) of 0.23–0.29. Lignin syringyl/guaiacyl (S/G) ratio and wood density were the most heritable traits (h2 = 0.42 and 0.59, respectively). Sugar release traits were positively correlated, phenotypically and genetically, with biomass yield and lignin S/G ratio. Association mapping revealed seven marker–trait associations below a suggestive significance threshold, including one marker associated with glucose release. We identified lignin S/G ratio and shoot diameter as heritable traits that could be relatively easily evaluated by breeders, making them suitable proxy traits for developing low-recalcitrance varieties. One marker below the suggestive threshold for marker associations was identified for sugar release, meriting further investigation while also highlighting the difficulties in employing genomewide association mapping for complex traits.
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polymorphism and divergence in two willow species Salix viminalis l and Salix schwerinii e wolf
G3: Genes Genomes Genetics, 2011Co-Authors: Sofia Berlin, Martin Lascoux, Ulf Lagercrantz, Johan Fogelqvist, Annchristin RonnbergwastljungAbstract:We investigated species divergence, present and past gene flow, levels of nucleotide polymorphism, and linkage disequilibrium in two willows from the plant genus Salix. Salix belongs together with Populus to the Salicaceae family; however, most population genetic studies of Salicaceae have been performed in Populus, the model genus in forest biology. Here we present a study on two closely related willow species Salix viminalis and S. schwerinii, in which we have resequenced 33 and 32 nuclear gene segments representing parts of 18 nuclear loci in 24 individuals for each species. We used coalescent simulations and estimated the split time to around 600,000 years ago and found that there is currently limited gene flow between the species. Mean intronic nucleotide diversity across gene segments was slightly higher in S. schwerinii (πi = 0.00849) than in S. viminalis (πi = 0.00655). Compared with other angiosperm trees, the two willows harbor intermediate levels of silent polymorphisms. The decay of linkage disequilibrium was slower in S. viminalis compared with S. schwerinii, and we speculate that this is due to different demographic histories as S. viminalis has been partly domesticated in Europe.
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qtl analyses of drought tolerance and growth for a Salix dasyclados Salix viminalis hybrid in contrasting water regimes
Theoretical and Applied Genetics, 2005Co-Authors: Annchristin Ronnbergwastljung, Carolyn Glynn, Martin WeihAbstract:Quantitative trait loci (QTL) for growth traits and water-use efficiency have been identified in two water regimes (normal and drought-treated) and for a treatment index. A tetraploid hybrid F2 population originating from a cross between a Salix dasyclados clone (SW901290) and a Salix viminalis clone (‘Jorunn’) was used in the study. The growth response of each individual including both above and below ground dry-matter production (i.e. shoot length, shoot diameter, aboveground and root dry weight, internode length, root dry weight/total dry weight, relative growth rate and leaf nitrogen content) was analysed in a replicated block experiment with two water treatments. A composite interval mapping approach was used to estimate number of QTL, the magnitude of the QTL and their position on genetic linkage maps. QTL specific for each treatment and for the treatment index were found, but QTL common across the treatments and the treatment index were also detected. Each QTL explained from 8% to 29% of the phenotypic variation, depending on trait and treatment. Clusters of QTL for different traits were mapped close to each other at several linkage groups, indicating either a common genetic base or tightly linked QTL. Common QTL identified between treatments and treatment index in the complex trait dry weight can be useful tools in the breeding and selection for drought stress tolerance in Salix.
Domenico Morabito - One of the best experts on this subject based on the ideXlab platform.
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Amending an As/Pb contaminated soil with biochar, compost and iron grit: effect on Salix viminalis growth, root proteome profiles and metal(loid) accumulation indexes
Chemosphere, 2020Co-Authors: Manhattan Lebrun, Florie Miard, Gabriella S. Scippa, Sylvain Bourgerie, Domenico Morabito, Giovanni Renzone, Andrea Scaloni, Dalila TrupianoAbstract:There is currently a large amount of research being done into the phytoremediation of polluted soils. Plant installation in contaminated soils may require the application of soil amendments, such as biochar, compost and/or iron grit, which can improve the soil conditions and reduce the metal (loid) phytoavailability and mobility. The beneficial effects of these amendments on soil properties, plant growth and metal (loid) accumulation ability have already been described, although their effect on the plants response machinery has been poorly studied. This study aimed to assess the effect of these amendments on Salix viminalis growth and metal (loid) accumulation, as well as elucidating associated molecular mechanisms. The results showed that the amendment applications improved plant growth by three fold, except for the biochar plus iron combination. It also revealed that metal (loid)s were not effectively translocated from the roots to the shoots (translocation factors
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Biochar effect associated with compost and iron to promote Pb and As soil stabilization and Salix viminalis L. growth
Chemosphere, 2019Co-Authors: Manhattan Lebrun, Florie Miard, Romain Nandillon, Gabriella S. Scippa, Sylvain Bourgerie, Domenico MorabitoAbstract:Soil pollution by metal(loid)s is one of the most significant problems in Europe. To remediate and potentially rehabilitate these contaminated sites, phytoremediation procedures are being put into place, often using amendments to help offset the extreme conditions of such soils. The aim of this study was to define the best amendment to use on the field. This was done by studying how the addition of three different amendments (biochar, compost and iron grit), alone or in combination, could affect: (i) soil physico-chemical properties, (ii) Salix viminalis growth, and (iii) metal(loid) stabilization. A 69 day-mesocosm study was thus set up using a former mine technosol, the three amendments applied alone or combined, and S. viminalis cuttings. The results showed that biochar and/or compost improved the soil fertility and the soil pore water characteristics, with reductions of acidity, metal(loid) mobility and toxicity, while iron grit amendment presented negative effects on such parameters. Such ameliorations allowed better plant growth and higher biomass production. In addition, stress indicators (leaf pigment content and root guaiacol peroxidase activity) showed a reduction in plant stress following biochar and/or compost application. Finally, among the different treatments, the use of compost or a biochar-compost combination showed better results in terms of improvement of soil conditions, increase in plant growth and reduced translocation of metal(loid)s towards upper parts, making these two treatments a valuable option for a field trial.
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Eco-restoration of a mine technosol according to biochar particle size and dose application: study of soil physico-chemical properties and phytostabilization capacities of Salix viminalis
Journal of Soils and Sediments, 2018Co-Authors: Manhattan Lebrun, Florie Miard, Romain Nandillon, Nour Hattab-hambli, Gabriella S. Scippa, Sylvain Bourgerie, Domenico MorabitoAbstract:Purpose Anthropic activities induce severe metal(loid)s contamination of many sites, which is a threat to the environment and to public health. Indeed metal(loid)s cannot be degraded, and thus accumulate in soils. Furthermore, they can contaminate surrounding ecosystems through run-off or wind erosion. This study aims to evaluate the phytostabilization capacity of Salix viminalis to remediate As and Pb highly contaminated mine site, in a biochar-assisted phytoremediation context and to assess biochar particle size and dose application effects. Materials and methods To achieve this, mesocosm experiments were conducted using the contaminated technosol and four different size fraction of one biochar as amendment, at two application rates (2 and 5%). Non-rooted cuttings of Salix viminalis were planted in the different mixtures. In order to characterize the mixtures, soil pore waters were sampled at the beginning and at the end of the experiment and analyzed for pH, electrical conductivity, and metal(loid) concentrations. After 46 days of Salix growth, roots, stems, and leaves were harvested and weighed, and As and Pb concentrations and distributions were measured. Results and discussion Soil fertility improved (acidity decrease, electrical conductivity increase) following biochar addition, whatever the particle size, and the Pb concentration in soil pore water decreased. Salix viminalis did not grow on the non-amended contaminated soil while the biochar amendment permitted its growth, with a better growth with the finest biochars. The metal(loid)s accumulated preferentially in roots. Conclusions Fine biochar particles allowed S. viminalis growth on the contaminated soil, allowing this species to be used for technosol phytostabilization.
Martin Lascoux - One of the best experts on this subject based on the ideXlab platform.
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polymorphism and divergence in two willow species Salix viminalis l and Salix schwerinii e wolf
G3: Genes Genomes Genetics, 2011Co-Authors: Sofia Berlin, Martin Lascoux, Ulf Lagercrantz, Johan Fogelqvist, Annchristin RonnbergwastljungAbstract:We investigated species divergence, present and past gene flow, levels of nucleotide polymorphism, and linkage disequilibrium in two willows from the plant genus Salix. Salix belongs together with Populus to the Salicaceae family; however, most population genetic studies of Salicaceae have been performed in Populus, the model genus in forest biology. Here we present a study on two closely related willow species Salix viminalis and S. schwerinii, in which we have resequenced 33 and 32 nuclear gene segments representing parts of 18 nuclear loci in 24 individuals for each species. We used coalescent simulations and estimated the split time to around 600,000 years ago and found that there is currently limited gene flow between the species. Mean intronic nucleotide diversity across gene segments was slightly higher in S. schwerinii (πi = 0.00849) than in S. viminalis (πi = 0.00655). Compared with other angiosperm trees, the two willows harbor intermediate levels of silent polymorphisms. The decay of linkage disequilibrium was slower in S. viminalis compared with S. schwerinii, and we speculate that this is due to different demographic histories as S. viminalis has been partly domesticated in Europe.
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Genetic mapping of sex-linked markers in Salix viminalis L.
Heredity, 2003Co-Authors: Vladimir L. Semerikov, C Alstrom-rapaport, Ann-christin Rönnberg-wästljung, Ulf Lagercrantz, V. Tsarouhas, Martin LascouxAbstract:A total of 88 selective primer combinations were screened using bulked males and females sampled from four families of Salix viminalis. A total of more than 1000 polymorphic fragments was obtained, of which only four cosegregated with sex. These four sex-linked markers were subsequently scored in individuals that were used for bulked sample preparation in additional individuals of the same families, and in individuals in other families. A pair of primers that amplified the sex-linked fragments was constructed from one of the sex-linked amplified fragment length polymorphism (AFLP) fragments. In hybridization of Southern blot filters with the sex-linked DNA fragments, the band was present in females and absent in males, but the opposite pattern of band segregation (a band found in males and no band in females) was never observed in either the AFLP or RFLP experiments. Two of the sex-linked markers were placed on a linkage map. They both map at the same location in a linkage group comprising other markers not segregating with sex. Our data suggest that a single locus governs the sex determination and that nonrecombining sex chromosomes are absent in S. viminalis. A close association was found between skewed sex ratio and segregation distortion at this locus.
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genetic structure of melampsora epitea populations in swedish Salix viminalis plantations
European Journal of Plant Pathology, 2001Co-Authors: Berit Samils, Martin Lascoux, Ulf Lagercrantz, Urban GullbergAbstract:Amplified fragment length polymorphism (AFLP) was used to study the genetic structure of populations of the willow leaf rust, Melampsora epitea, in Swedish willow plantations. In total, 197 isolates collected from Salix viminalis clones in three locations in Sweden were analysed. AFLP profiles based on 83 markers were used to compute genetic distances between pairs of individuals. High levels of gene and genotypic diversity were detected in all populations, with 96% of the AFLP loci being polymorphic and with normalized Shannon's diversity indices ranging from 0.977 to 1.0. Analysis of molecular variance (AMOVA) showed small significant differences among locations, although most of the molecular variability was found within locations (97.5%). Five isolates from one willow clone in one location differed markedly from the common pattern. When these five exceptional isolates were excluded, no significant differences among willow clones were found with AMOVA. Sexual reproduction and spore migration appear to be important factors for the population genetic structure of this pathogen.
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Identification of a RAPD marker linked to sex determination in the basket willow (Salix viminalis L.)
Journal of Heredity, 1998Co-Authors: C Alstrom-rapaport, Martin Lascoux, Yc Wang, G. T. Roberts, Gerald A. TuskanAbstract:In many dioecious plants, gender influences economic value, breeding schemes, and/or opportunities for commercial use of genetically transformed materials. The objective of this study was to identify molecular markers linked to sex determination loci in the dioecious plant Salix viminalis L. A 4 3 4 factorial mating design was used to identify sex ratios in full-sibling progeny, to generate a working genetics model for segregating sex ratios, and to search for molecular markers linked to sex determination genes. Bulked segregant analysis, utilizing 380 arbitrary decamer primers to generate randomly amplified polymorphic DNA (RAPD) products was initially applied to progeny sets from 3 of the 16 full-sibling families. Of the 1080 RAPD bands examined, only a single 560 bp band was shown to be linked to a sex determination locus. The same 560 bp band occurred in three additional fullsibling families and was present in one female parent and one male parent involved in the factorial mating design. This marker, UBC354560, is biparentally inherited, is associated with femaleness in certain genetic backgrounds, and is linked to allele A1 in the proposed two-locus epistatic genetic model of sex determination for S. viminalis. Southern blots confirmed marker homology among progeny and parents used in this study.
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Sex determination and sex ratio in the dioecious shrub Salix viminalis L.
Theoretical and Applied Genetics, 1997Co-Authors: C Alstrom-rapaport, Martin Lascoux, Urban GullbergAbstract:Various ecological factors (e.g. herbivory, difference between males and females in colonising ability) have been invoked to explain female-biased sex ratios in populations of willow species. It was implicitly assumed that genetic factors would lead to a balanced sex ratio in the absence of ecological disturbances. In an experiment carried out in a homogeneous environment and in the absence of herbivores the progeny sex ratio of 13 crosses of basket willow (Salix viminalis L.) was observed to range from extreme female bias to extreme male bias. The observed sex ratio cannot be explained by the presence of sex chromosomes without assuming that additional loci are also involved in the sex determination. Alternatively, the sex ratios in this study can be explained by a sex determination mechanism governed by multiple independent loci.
Manhattan Lebrun - One of the best experts on this subject based on the ideXlab platform.
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Amending an As/Pb contaminated soil with biochar, compost and iron grit: effect on Salix viminalis growth, root proteome profiles and metal(loid) accumulation indexes
Chemosphere, 2020Co-Authors: Manhattan Lebrun, Florie Miard, Gabriella S. Scippa, Sylvain Bourgerie, Domenico Morabito, Giovanni Renzone, Andrea Scaloni, Dalila TrupianoAbstract:There is currently a large amount of research being done into the phytoremediation of polluted soils. Plant installation in contaminated soils may require the application of soil amendments, such as biochar, compost and/or iron grit, which can improve the soil conditions and reduce the metal (loid) phytoavailability and mobility. The beneficial effects of these amendments on soil properties, plant growth and metal (loid) accumulation ability have already been described, although their effect on the plants response machinery has been poorly studied. This study aimed to assess the effect of these amendments on Salix viminalis growth and metal (loid) accumulation, as well as elucidating associated molecular mechanisms. The results showed that the amendment applications improved plant growth by three fold, except for the biochar plus iron combination. It also revealed that metal (loid)s were not effectively translocated from the roots to the shoots (translocation factors
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Biochar effect associated with compost and iron to promote Pb and As soil stabilization and Salix viminalis L. growth
Chemosphere, 2019Co-Authors: Manhattan Lebrun, Florie Miard, Romain Nandillon, Gabriella S. Scippa, Sylvain Bourgerie, Domenico MorabitoAbstract:Soil pollution by metal(loid)s is one of the most significant problems in Europe. To remediate and potentially rehabilitate these contaminated sites, phytoremediation procedures are being put into place, often using amendments to help offset the extreme conditions of such soils. The aim of this study was to define the best amendment to use on the field. This was done by studying how the addition of three different amendments (biochar, compost and iron grit), alone or in combination, could affect: (i) soil physico-chemical properties, (ii) Salix viminalis growth, and (iii) metal(loid) stabilization. A 69 day-mesocosm study was thus set up using a former mine technosol, the three amendments applied alone or combined, and S. viminalis cuttings. The results showed that biochar and/or compost improved the soil fertility and the soil pore water characteristics, with reductions of acidity, metal(loid) mobility and toxicity, while iron grit amendment presented negative effects on such parameters. Such ameliorations allowed better plant growth and higher biomass production. In addition, stress indicators (leaf pigment content and root guaiacol peroxidase activity) showed a reduction in plant stress following biochar and/or compost application. Finally, among the different treatments, the use of compost or a biochar-compost combination showed better results in terms of improvement of soil conditions, increase in plant growth and reduced translocation of metal(loid)s towards upper parts, making these two treatments a valuable option for a field trial.
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Eco-restoration of a mine technosol according to biochar particle size and dose application: study of soil physico-chemical properties and phytostabilization capacities of Salix viminalis
Journal of Soils and Sediments, 2018Co-Authors: Manhattan Lebrun, Florie Miard, Romain Nandillon, Nour Hattab-hambli, Gabriella S. Scippa, Sylvain Bourgerie, Domenico MorabitoAbstract:Purpose Anthropic activities induce severe metal(loid)s contamination of many sites, which is a threat to the environment and to public health. Indeed metal(loid)s cannot be degraded, and thus accumulate in soils. Furthermore, they can contaminate surrounding ecosystems through run-off or wind erosion. This study aims to evaluate the phytostabilization capacity of Salix viminalis to remediate As and Pb highly contaminated mine site, in a biochar-assisted phytoremediation context and to assess biochar particle size and dose application effects. Materials and methods To achieve this, mesocosm experiments were conducted using the contaminated technosol and four different size fraction of one biochar as amendment, at two application rates (2 and 5%). Non-rooted cuttings of Salix viminalis were planted in the different mixtures. In order to characterize the mixtures, soil pore waters were sampled at the beginning and at the end of the experiment and analyzed for pH, electrical conductivity, and metal(loid) concentrations. After 46 days of Salix growth, roots, stems, and leaves were harvested and weighed, and As and Pb concentrations and distributions were measured. Results and discussion Soil fertility improved (acidity decrease, electrical conductivity increase) following biochar addition, whatever the particle size, and the Pb concentration in soil pore water decreased. Salix viminalis did not grow on the non-amended contaminated soil while the biochar amendment permitted its growth, with a better growth with the finest biochars. The metal(loid)s accumulated preferentially in roots. Conclusions Fine biochar particles allowed S. viminalis growth on the contaminated soil, allowing this species to be used for technosol phytostabilization.
Sofia Berlin - One of the best experts on this subject based on the ideXlab platform.
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recent sex chromosome divergence despite ancient dioecy in the willow Salix viminalis
Molecular Biology and Evolution, 2017Co-Authors: Pascal Pucholt, Alison E Wright, Lei Liu Conze, Judith E Mank, Sofia BerlinAbstract:Sex chromosomes can evolve when recombination is halted between a pair of chromosomes, and this can lead to degeneration of the sex-limited chromosome. In the early stages of differentiation sex chromosomes are homomorphic, and even though homomorphic sex chromosomes are very common throughout animals and plants, we know little about the evolutionary forces shaping these types of sex chromosomes. We used DNA- and RNA-Seq data from females and males to explore the sex chromosomes in the female heterogametic willow, Salix viminalis, a species with ancient dioecy but with homomorphic sex chromosomes. We detected no major sex differences in read coverage in the SD region, indicating that the W region has not significantly degenerated. However, SNP densities in the SD region are higher in females compared to males, indicating very recent recombination suppression, followed by the accumulation of sex-specific SNPs. Interestingly, we identified two female-specific scaffolds that likely represent W-chromosome-specific sequence. We show that genes located in the SD region display a mild excess of male-biased expression in sex-specific tissue, and we use allele-specific gene expression analysis to show that this is the result of masculinization of expression on the Z chromosome rather than degeneration of female-expression on the W chromosome. Together, our results demonstrate that insertion of small DNA fragments and accumulation of sex-biased gene expression can occur before the detectable decay of the sex-limited chromosome.
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genetic diversity population structure and phenotypic variation in european Salix viminalis l salicaceae
Tree Genetics & Genomes, 2014Co-Authors: Sofia Berlin, I Shield, Henrik R Hallingback, Inger Åhman, Johan Fogelqvist, Sviatlana Trybush, Niclas Gyllenstrand, Ne Nordh, Stephen J Powers, Martin WeihAbstract:To investigate the potential of association genetics for willow breeding, Salix viminalis germplasm was assembled from UK and Swedish collections (comprising accessions from several European countries) and new samples collected from nature. A subset of the germplasm was planted at two sites (UK and Sweden), genotyped using 38 SSR markers and assessed for phenological and biomass traits. Population structure, genetic differentiation (F ST ) and quantitative trait differentiation (Q ST ) were investigated. The extent and patterns of trait adaptation were assessed by comparing F ST and Q ST parameters. Of the 505 genotyped diploid accessions, 27 % were not unique. Genetic diversity was high: 471 alleles was amplified; the mean number of alleles per locus was 13.46, mean observed heterozygosity was 0.55 and mean expected heterozygosity was 0.62. Bayesian clustering identified four subpopulations which generally corresponded to Western Russia, Western Europe, Eastern Europe and Sweden. All pairwise F ST values were highly significant (p < 0.001) with the greatest genetic differentiation detected between the Western Russian and the Western European subpopulations (F ST = 0.12), and the smallest between the Swedish and Eastern European populations (F ST = 0.04). The Swedish population also had the highest number of identical accessions, supporting the view that S. viminalis was introduced into this country and has been heavily influenced by humans. Q ST values were high for growth cessation and leaf senescence, and to some extent stem diameter, but low for bud burst time and shoot number. Overall negative clines between longitudinal coordinates and leaf senescence, bud burst and stem diameter were also found.
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polymorphism and divergence in two willow species Salix viminalis l and Salix schwerinii e wolf
G3: Genes Genomes Genetics, 2011Co-Authors: Sofia Berlin, Martin Lascoux, Ulf Lagercrantz, Johan Fogelqvist, Annchristin RonnbergwastljungAbstract:We investigated species divergence, present and past gene flow, levels of nucleotide polymorphism, and linkage disequilibrium in two willows from the plant genus Salix. Salix belongs together with Populus to the Salicaceae family; however, most population genetic studies of Salicaceae have been performed in Populus, the model genus in forest biology. Here we present a study on two closely related willow species Salix viminalis and S. schwerinii, in which we have resequenced 33 and 32 nuclear gene segments representing parts of 18 nuclear loci in 24 individuals for each species. We used coalescent simulations and estimated the split time to around 600,000 years ago and found that there is currently limited gene flow between the species. Mean intronic nucleotide diversity across gene segments was slightly higher in S. schwerinii (πi = 0.00849) than in S. viminalis (πi = 0.00655). Compared with other angiosperm trees, the two willows harbor intermediate levels of silent polymorphisms. The decay of linkage disequilibrium was slower in S. viminalis compared with S. schwerinii, and we speculate that this is due to different demographic histories as S. viminalis has been partly domesticated in Europe.
