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When environmental conditions differ both within and among populations, multiscale adaptation results from processes at both scales and interference across scales. We hypothesize that within-population environmental heterogeneity influences the chance of success of migration events, both within and among populations, and maintains within-population adaptive differentiation. We used a simulation approach to analyse the joint effects of environmental heterogeneity patterns, selection intensity and number of QTL controlling a selected trait on local adaptation in a hierarchical metapopulation design. We show the general effects of within-population environmental heterogeneity: (i) it increases occupancy rate at the margins of distribution ranges, under extreme environments and high levels of selection; (ii) it increases the adaptation lag in all environments; (iii) it impacts the genetic variance in each environment, depending on the ratio of within- to between-populations environmental heterogeneity; (iv) it reduces the selection-induced erosion of adaptive gene diversity. Most often, the smaller the number of QTL involved, the stronger are these effects. We also show that both within- and between-populations phenotypic differentiation (Q

Humans have had a major influence on the dissemination of crops beyond their native range, thereby offering new hybridization opportunities. Characterizing admixed genomes with mosaic origins generates valuable insight into the adaptive history of crops and the impact on current varietal diversity. We applied the ELAI tool—an efficient local ancestry inference method based on a two-layer hidden Markov model to track segments of wild origin in cultivated accessions in the case of multiway admixtures. Source populations—which may actually be limited and partially admixed—must be generally specified when using such inference models. We thus developed a framework to identify local ancestry with admixed source populations. Using sequencing data for wild and cultivated Coffea canephora (commonly called Robusta), our approach was found to be highly efficient and accurate on simulated hybrids. Application of the method to assess elite Robusta varieties from Vietnam led to the identification of an accession derived from a likely backcross between two genetic groups from the Congo Basin and the western coastal region of Central Africa. Admixtures resulting from crop hybridization and diffusion could thus lead to the generation of elite high-yielding varieties. Our methods should be widely applicable to gain insight into the role of hybridization during plant and animal evolutionary history.

Zero hunger and good health could be realized by 2030 through effective conservation, characterization and utilization of germplasm resources1. So far, few chickpea (Cicer arietinum) germplasm accessions have been characterized at the genome sequence level2. Here we present a detailed map of variation in 3,171 cultivated and 195 wild accessions to provide publicly available resources for chickpea genomics research and breeding. We constructed a chickpea pan-genome to describe genomic diversity across cultivated chickpea and its wild progenitor accessions. A divergence tree using genes present in around 80% of individuals in one species allowed us to estimate the divergence of Cicer over the last 21 million years. Our analysis found chromosomal segments and genes that show signatures of selection during domestication, migration and improvement. The chromosomal locations of deleterious mutations responsible for limited genetic diversity and decreased fitness were identified in elite germplasm. We identified superior haplotypes for improvement-related traits in landraces that can be introgressed into elite breeding lines through haplotype-based breeding, and found targets for purging deleterious alleles through genomics-assisted breeding and/or gene editing. Finally, we propose three crop breeding strategies based on genomic prediction to enhance crop productivity for 16 traits while avoiding the erosion of genetic diversity through optimal contribution selection (OCS)-based pre-breeding. The predicted performance for 100-seed weight, an important yield-related trait, increased by up to 23% and 12% with OCS- and haplotype-based genomic approaches, respectively., Whole-genome sequencing of 3,171 cultivated and 195 wild chickpea accessions is used to construct a chickpea pan-genome, providing insight into chickpea evolution and enabling breeding strategies that could improve crop productivity.

Geographical distribution and diversity of current plant species have been strongly shaped by climatic oscillations during the Quaternary. Analysing the resulting divergence among species and differentiation within species is crucial to understand the evolution of taxa like the Vitis genus, which provides very useful genetic resources for grapevine improvement and might reveal original recolonization patterns due to growth habit and dispersal mode. Here, we studied the genetic structure in natural populations of three species from eastern North America: Vitis aestivalis, V. cinerea and V. riparia using different marker types. Vitis aestivalis and V. cinerea showed higher diversity than V. riparia. The two former species are less differentiated, confirming an earlier divergence of V. riparia. V. aestivalis and V. riparia exhibited different genetic groups on both sides of the Appalachian Mountains that could mirror different recolonization routes from southern refugia. Genetic structure was stronger in V. cinerea, for which two varieties (var. berlandieri and var. cinerea) are morphologically recognized. Our results confirm this distinction and suggest the existence of three other lineages within var. cinerea. These discontinuities appear linked to adaptation of var. berlandieri to dry and limy areas of Texas and partially to the Mississippi River Valley. Rapid range expansions from refugia upon climate warming are also suggested by the low linkage disequilibrium values observed. Furthermore, large variation for downy mildew resistance was observed in the three species. Our findings appeared consistent with the vegetation history of eastern North America.

BackgroundAfrican rice, Oryza glaberrima, is an invaluable resource for rice cultivation and for the improvement of biotic and abiotic resistance properties. Since its domestication in the inner Niger delta ca. 2500 years BP, African rice has colonized a variety of ecologically and climatically diverse regions. However, little is known about the genetic basis of quantitative traits and adaptive variation of agricultural interest for this species.ResultsUsing a reference set of 163 fully re-sequenced accessions, we report the results of a Genome Wide Association Study carried out for African rice. We investigated a diverse panel of traits, including flowering date, panicle architecture and resistance to Rice yellow mottle virus. For this, we devised a pipeline using complementary statistical association methods. First, using flowering time as a target trait, we demonstrated that we could successfully retrieve known genes from the rice flowering pathway, and identified new genomic regions that would deserve more study. Then we applied our pipeline to panicle- and resistance-related traits, highlighting some interesting QTLs and candidate genes (including Rymv1 for resistance and SP1, Ghd7.1, APO1 and OsMADS1 for panicle architecture). Lastly, using a high-resolution climate database, we performed an association analysis based on climatic variables, searching for genomic regions that might be involved in adaptation to climatic variations.ConclusionOur results collectively provide insights into the extent to which adaptive variation is governed by sequence diversity within the O. glaberrima genome, paving the way for in-depth studies of the genetic basis of traits of interest that might be useful to the rice breeding community.

Improving crop water use efficiency, the amount of carbon assimilated as biomass per unit of water used by a plant, is of major importance as water for agriculture becomes scarcer. In rice, the genetic bases of transpiration efficiency, the derivation of water use efficiency at the whole-plant scale, and its putative component trait transpiration restriction under high evaporative demand remain unknown. These traits were measured in 2019 in a panel of 147 African rice (Oryza glaberrima) genotypes known to be potential sources of tolerance genes to biotic and abiotic stresses. Our results reveal that higher transpiration efficiency is associated with transpiration restriction in African rice. Detailed measurements in a subset of highly contrasted genotypes in terms of biomass accumulation and transpiration confirmed these associations and suggested that root to shoot ratio played an important role in transpiration restriction. Genome wide association studies identified marker-trait associations for transpiration response to evaporative demand, transpiration efficiency, and its residuals, with links to genes involved in water transport and cell wall patterning. Our data suggest that root-shoot partitioning is an important component of transpiration restriction that has a positive effect on transpiration efficiency in African rice. Both traits are heritable and define targets for breeding rice with improved water use strategies., This work was supported by the Institut de Recherche pour le Développement, the CGIAR Research Program (CRP) on rice-agrifood systems (RICE, 2017-2022) and the Agence Nationale de la Recherche (grant ANR-17-MPGA-0011 to VV). Financial support by the Access to Research Infrastructures activity in the Horizon 2020 Programme of the EU (EPPN2020 Grant Agreement 731013) is gratefully acknowledged. PA was supported by a doctoral fellowship from the French Ministry of Higher Education. BEE was supported by the Centre National de la Recherche Scientifique et Technologique of Gabon. The authors acknowledge the IRD iTrop HPC (South Green Platform) at IRD Montpellier for providing HPC resources (https://bioinfo.ird.fr, http://www.southgreen.fr).

Because water availability is the most important environmental factor limiting crop production, improving water use efficiency, the amount of carbon fixed per water used, is a major target for crop improvement. In rice, the genetic bases of transpiration efficiency, the derivation of water use efficiency at the whole-plant scale, and its putative component trait transpiration restriction under high evaporative demand, remain unknown. These traits were measured in a panel of 147 African rice Oryza glaberrima genotypes, known as potential sources of tolerance genes to biotic and abiotic stresses. Our results reveal that higher transpiration efficiency is associated with transpiration restriction in African rice. Detailed measurements in a subset of highly differentiated genotypes confirmed these associations and suggested that the root to shoot ratio played an important role in transpiration restriction. Genome wide association studies identified marker-trait associations for transpiration response to evaporative demand, transpiration efficiency and its residuals, that links to genes involved in water transport and cell wall patterning. Our data suggest that root shoot partitioning is an important component of transpiration restriction that has a positive effect on transpiration efficiency in African rice. Both traits are heritable and define targets for breeding rice with improved water use strategies.

The rhizosheath, the layer of soil that adheres strongly to roots, influences water and nutrients acquisition. Pearl millet is a cereal crop that plays a major role for food security in arid regions of sub Saharan Africa and India. We previously showed that root-adhering soil mass is a heritable trait in pearl millet and that it correlates with changes in rhizosphere microbiota structure and functions. Here, we studied the correlation between root-adhering soil mass and root hair development, root architecture, and symbiosis with arbuscular mycorrhizal fungi and we analysed the genetic control of this trait using genome wide association (GWAS) combined with bulk segregant analysis and gene expression studies. Root-adhering soil mass was weakly correlated only to root hairs traits in pearl millet. Twelve QTLs for rhizosheath formation were identified by GWAS. Bulk segregant analysis on a biparental population validated five of these QTLs. Combining genetics with a comparison of global gene expression in the root tip of contrasted inbred lines revealed candidate genes that might control rhizosheath formation in pearl millet. Our study indicates that rhizosheath formation is under complex genetic control in pearl millet and suggests that it is mainly regulated by root exudation.HighlightFormation of the rhizosheath, a layer of soil adhering to the root, is under complex genetic control in pearl millet and is mainly regulated by root exudation.

Background: In West Africa, two rice species are cultivated, the African rice Oryza glaberrima and the Asian rice Oryza sativa, the second one being much more frequent. Despite its importance for food security in West Africa, the genetic diversity of Oryza sativa in farmer’s fields remains understudied in this region. Documenting the dynamics of diversity in the fields between landraces and improved cultivars is of importance to ensure rice cultivation adaptation to global change.In this study, we genotyped 77 rice samples from Burkina Faso using the C6AIR SNP array from IRRI. Among the studied samples, 27 were certified cultivars and 50 were sampled in rice fields from three geographical zones in western Burkina Faso, each zone comprising one irrigated area and a neighboring rainfed lowland. Obtained data were analyzed in the frame of the worldwide rice genetic diversity by using the 3K genomes as reference.Results: Most of the certified cultivars clustered with the indica genetic group, with a minority (26%) assigned to the japonica group. All except one of the rice samples from farmer’s fields belonged to the indica group. The peculiar one unexpectedly clustered with the Aus genetic group and originated from Tengrela (rainfed lowland in Karfiguela zone). This site, already known to differ in terms of agronomic practices, showed the highest genetic diversity compared to the five other sites, as well as highest genetic differentiation. Obtained genetic data confirmed the high global frequency of one cultivar, in accordance with the data from farmer’s interview. However, at the field level, genetic data rarely corresponded to the cultivar’s names obtained from farmer’s interviews.Conclusions: Overall we found a high genetic diversity in the studied samples from Burkina Faso (certified and field’s samples). We argue on the importance to document and preserve this agro-biodiversity as a prerequisite to face the current challenges of growing rice demand and global change. To this purpose, are required further scientific studies to refine our understanding of the dynamics of diversity in farmers’ fields, as well as a better knowledge of rice agro-biodiversity and awareness of its importance by rice farmers themselves.

Despite constituting the western-most edge of the population distributions for several native European plants, Ireland has largely been left out of key Europe-wide phylogeographic studies. This is true for birch (Betula pubescens Ehrh. and Betula pendula Roth), for which the genetic diversity has yet to be mapped for Ireland. Here we used eight cpDNA markers (two Restriction Fragment Length Polymorphism (RFLP) and six Simple Sequence Repeat (SSR)) to map the genetic diversity of B. pubescens, B. pendula, and putative hybrid individuals sampled from 19 populations spread cross most of the island of Ireland. Within Ireland, 11 distinct haplotypes were detected, the most common of which (H1) was also detected in England, Scotland, France, and Norway. A moderate level of population structuring (GST = 0.282) was found across Ireland and the genetic diversity of its northern populations was twice that of its southern populations. This indicates that, unlike other native Irish trees, such as oak and alder, post-glacial recolonization by birch did not begin in the south (i.e., from Iberia). Rather, and in agreement with palynological data, birch most likely migrated in from eastern populations in Britain. Finally, we highlight Irish populations with comparatively unique genetic structure which may be included as part of European genetic conservation networks.

Sustainable food production in the context of climate change necessitates diversification of agriculture and a more efficient utilization of plant genetic resources. Fonio millet (Digitaria exilis) is an orphan African cereal crop with a great potential for dryland agriculture. Here, we establish high-quality genomic resources to facilitate fonio improvement through molecular breeding. These include a chromosome-scale reference assembly and deep re-sequencing of 183 cultivated and wild Digitaria accessions, enabling insights into genetic diversity, population structure, and domestication. Fonio diversity is shaped by climatic, geographic, and ethnolinguistic factors. Two genes associated with seed size and shattering showed signatures of selection. Most known domestication genes from other cereal models however have not experienced strong selection in fonio, providing direct targets to rapidly improve this crop for agriculture in hot and dry environments., Fonio millet is a fast growing orphan cereal crop with a great potential for dryland agriculture. Here, the authors report chromosome-scale reference genome assembly and population genomic resources to shed light on genetic diversity, population structure and domestication of fonio millet.

Draft genome, 994 re-sequenced lines and GWAS for yield-traits provide a resource of genetics and genomics tools for pearl millet researchers and breeders. Supplementary information The online version of this article (doi:10.1038/nbt.3943) contains supplementary material, which is available to authorized users., Pearl millet [Cenchrus americanus (L.) Morrone] is a staple food for more than 90 million farmers in arid and semi-arid regions of sub-Saharan Africa, India and South Asia. We report the ∼1.79 Gb draft whole genome sequence of reference genotype Tift 23D2B1-P1-P5, which contains an estimated 38,579 genes. We highlight the substantial enrichment for wax biosynthesis genes, which may contribute to heat and drought tolerance in this crop. We resequenced and analyzed 994 pearl millet lines, enabling insights into population structure, genetic diversity and domestication. We use these resequencing data to establish marker trait associations for genomic selection, to define heterotic pools, and to predict hybrid performance. We believe that these resources should empower researchers and breeders to improve this important staple crop. Supplementary information The online version of this article (doi:10.1038/nbt.3943) contains supplementary material, which is available to authorized users.

International audience; We report a map of 4.97 million single-nucleotide polymorphisms of the chickpea from whole-genome resequencing of 429 lines sampled from 45 countries. We identified 122 candidate regions with 204 genes under selection during chickpea breeding. Our data suggest the Eastern Mediterranean as the primary center of origin and migration route of chickpea from the Mediterranean/Fertile Crescent to Central Asia, and probably in parallel from Central Asia to East Africa (Ethiopia) and South Asia (India). Genome-wide association studies identified 262 markers and several candidate genes for 13 traits. Our study establishes a foundation for large-scale characterization of germplasm and population genomics, and a resource for trait dissection, accelerating genetic gains in future chickpea breeding.

International audience; African rice (Oryza glaberrima) was domesticated independently from Asian rice. The geographical origin of its domestication remains elusive. Using 246 new whole-genome sequences, we inferred the cradle of its domestication to be in the Inner Niger Delta. Domestication was preceded by a sharp decline of most wild populations that started more than 10.000 years ago. The wild population collapse occurred during the drying of the Sahara. This finding supports the hypothesis that depletion of wild resources in the Sahara triggered African rice domestication. African rice cultivation strongly expanded 2.000 years ago. During the last five centuries, a sharp decline of its cultivation coincided with the introduction of Asian rice in Africa. The gene PROG1 associated with an erect plant architecture phenotype, showed convergent selection in two rice cultivated species, Oryza glaberrima from Africa and Oryza sativa from Asia. In contrast, the shattering gene SH5 showed selection signature during African rice domestication, but not during Asian rice domestication. Overall, our genomic data reveal a complex history of African rice domestication influenced by important climatic changes in the Saharan area, by the expansion of African agricultural society, and by recent replacement by another domesticated species.; Le riz africain (Oryza glaberrima) a été domestiqué indépendamment du riz asiatique. L'origine géographique de sa domestication restait obscure. En utilisant 246 nouvelles séquences du génome complet, nous avons déduit que le berceau de sa domestication se trouvait dans le delta intérieur du Niger. Sa domestication a été précédée d'un fort déclin de la plupart des populations sauvages qui s’est amorcé il y a plus de 10.000 ans. L'effondrement des populations sauvages s'est produit pendant l'assèchement du Sahara. Cette découverte confirme l'hypothèse selon laquelle l'épuisement des ressources sauvages dans le Sahara a déclenché la domestication du riz africain. La culture du riz en Afrique s'est fortement développée il y a 2.000 ans. Au cours des cinq derniers siècles, le fort déclin de sa culture a coïncidé avec l'introduction du riz asiatique en Afrique. Le gène PROG1 associé à un phénotype d'architecture végétale érigée, a montré une sélection convergente pour deux espèces de riz cultivées, à savoir pour Oryza glaberrima d'Afrique et Oryza sativa d'Asie. En revanche, le gène d'éclatement SH5 a montré une signature de sélection pendant la domestication du riz africain, mais pas pendant la domestication du riz asiatique. Pour résumer, nos données génomiques révèlent une histoire complexe de la domestication du riz africain, influencée par les importants changements climatiques qu’a connu le Sahara, par une expansion des pratiques agricoles africaines, puis par le remplacement de cette céréale autochtone par des espèces domestiquées en Asie.

Q(ST) is a differentiation parameter based on the decomposition of the genetic variance of a trait. In the case of additive inheritance and absence of selection, it is analogous to the genic differentiation measured on individual loci, F(ST). Thus, Q(ST)−F(ST) comparison is used to infer selection: selective divergence when Q(ST) > F(ST), or convergence when Q(ST) < F(ST). The definition of Q-statistics was extended to two-level hierarchical population structures with Hardy–Weinberg equilibrium. Here, we generalize the Q-statistics framework to any hierarchical population structure. First, we developed the analytical definition of hierarchical Q-statistics for populations not at Hardy–Weinberg equilibrium. We show that the Q-statistics values obtained with the Hardy–Weinberg definition are lower than their corresponding F-statistics when F(IS) > 0 (higher when FIS < 0). Then, we used an island model simulation approach to investigate the impact of inbreeding and dominance on the Q(ST)−F(ST) framework in a hierarchical population structure. We show that, while differentiation at the lower hierarchical level (Q(SR)) is a monotonic function of migration, differentiation at the upper level (Q(RT)) is not. In the case of additive inheritance, we show that inbreeding inflates the variance of Q(RT), which can increase the frequency of Q(RT) > F(RT) cases. We also show that dominance drastically reduces Q-statistics below F-statistics for any level of the hierarchy. Therefore, high values of Q-statistics are good indicators of selection, but low values are not in the case of dominance.

The management of diversity for conservation and breeding is of great importance for all plant species and is particularly true in perennial species, such as the coffee Coffea canephora. This species exhibits a large genetic and phenotypic diversity with six different diversity groups. Large field collections are available in the Ivory Coast, Uganda and other Asian, American and African countries but are very expensive and time consuming to establish and maintain in large areas. We propose to improve coffee germplasm management through the construction of genetic core collections derived from a set of 565 accessions that are characterized with 13 microsatellite markers. Core collections of 12, 24 and 48 accessions were defined using two methods aimed to maximize the allelic diversity (Maximization strategy) or genetic distance (Maximum- Length Sub-Tree method). A composite core collection of 77 accessions is proposed for both objectives of an optimal management of diversity and breeding. This core collection presents a gene diversity value of 0.8 and exhibits the totality of the major alleles (i.e., 184) that are present in the initial set. The seven proposed core collections constitute a valuable tool for diversity management and a foundation for breeding programs. The use of these collections for collection management in research centers and breeding perspectives for coffee improvement are discussed.

Plant Breed.ISI Document Delivery No.: AJ4WPTimes Cited: 0Cited Reference Count: 31Cited References: Argout X, 2008, BMC GENOMICS, V9, DOI 10.1186/1471-2164-9-512 BESSE P, 1994, THEOR APPL GENET, V88, P199, DOI 10.1007/BF00225898 Conesa A, 2005, BIOINFORMATICS, V21, P3674, DOI 10.1093/bioinformatics/bti610 Cubry P, 2013, BMC GENOMICS, V14, DOI 10.1186/1471-2164-14-10 Ellis JR, 2007, HEREDITY, V99, P125, DOI 10.1038/sj.hdy.6801001 Feng SP, 2009, MOL BREEDING, V23, P85, DOI 10.1007/s11032-008-9216-0 Garcia D, 2011, PHYSIOL MOL PLANT P, V76, P126, DOI 10.1016/j.pmpp.2011.07.006 Gupta PK, 2005, PLANT MOL BIOL, V57, P461, DOI 10.1007/s11103-005-0257-z Gupta S, 2013, PLANT BREEDING, V132, P367, DOI 10.1111/pbr.12070 Kumar Yadav H., 2010, TREE GENET GENOMES, V7, P207 Le Guen V., 2008, EXPLORATION DIVERSIT Le Guen V, 2011, PLANT BREEDING, V130, P294, DOI 10.1111/j.1439-0523.2010.01774.x Le Guen V, 2009, TREE GENET GENOMES, V5, P673, DOI 10.1007/s11295-009-0218-9 Lespinasse D, 2000, THEOR APPL GENET, V100, P127, DOI 10.1007/s001220050018 Li DJ, 2012, BMC GENOMICS, V13, DOI 10.1186/1471-2164-13-192 Liu KJ, 2005, BIOINFORMATICS, V21, P2128, DOI 10.1093/bioinformatics/bti282 Ohyama A, 2009, MOL BREEDING, V23, P685, DOI 10.1007/s11032-009-9265-z Perovic D, 2009, MOL BREEDING, V23, P641, DOI 10.1007/s11032-009-9262-2 Perrier Xavier, 2003, P31 Perrier X., 2006, DARWIN SOFTWARE Pootakham W, 2012, PLANT BREEDING, V131, P555, DOI 10.1111/j.1439-0523.2012.01982.x Rafalski JA, 2010, CURR OPIN PLANT BIOL, V13, P174, DOI 10.1016/j.pbi.2009.12.004 Rozen S, 2000, Methods Mol Biol, V132, P365 SAITOU N, 1987, MOL BIOL EVOL, V4, P406 Seguin Marc, 2003, P277 Souza LM, 2009, CONSERV GENET RESOUR, V1, P75, DOI 10.1007/s12686-009-9018-7 Triwitayakorn K, 2011, DNA RES, V18, P471, DOI 10.1093/dnares/dsr034 Tyrka M, 2008, J APPL GENET, V49, P127, DOI 10.1007/BF03195605 Varshney RK, 2005, TRENDS BIOTECHNOL, V23, P48, DOI 10.1016/j.tibtech.2004.11.005 Vigouroux Y, 2005, GENETICS, V169, P1617, DOI 10.1534/genetics.104.032086 Wen Mingfu, 2010, BMC Res Notes, V3, P42, DOI 10.1186/1756-0500-3-42Cubry, Philippe Pujade-Renaud, Valerie Garcia, Dominique Espeout, Sandra Le Guen, Vincent Granet, Francoise Seguin, MarcFrench National Research Agency (Agence Nationale pour la Recherche; contrat ANR/Genoplante) [GPLA07017C]This work was performed as part of the CIRAD - Michelin collaborative project 'Genesalb' supported by a grant from the French National Research Agency (Agence Nationale pour la Recherche; contrat ANR/Genoplante no GPLA07017C). We thank the Montpellier Languedoc-Roussillon Grand plateau technique regional for hosting the SSR genotyping activities. ESTtik database was made available by the SouthGreen bioinformatics platform at http://southgreen.cirad.fr/. We thank Ronan Rivallan for technical help, Xavier Argout for computational procedures and data retrieving, Gerald Oliver for keeping some vegetal material in a greenhouse in Montpellier, Jean-Marc Thevenin and Fabien Doare for providing us with some fresh material from CIRAD's Pointe Combi Centre (French Guyana) collection.Wiley-blackwellHoboken; Despite its economic importance and recent genome release, the need for molecular tools for Hevea brasiliensis is high. In the frame of a disease resistance study, EST sequences were retrieved from public database or generated by sequencing SSH libraries. Sequences were trimmed and microsatellite motifs searched using an ad hoc bioinformatic pipeline, and pairs of primers for the amplification of candidate markers were generated. We found a total of 10499 unigenes from both sources of sequences, and 673 microsatellites motifs were detected using the default parameters of the pipeline. Two hundred sixty-four primer pairs were tested and 226 (85.6%) successfully amplified. Out of the amplified candidate markers, 164 exhibited polymorphism. Relationships based on dendrograms using simple matching index and diversity statistics based on EST-SSRs were compared with Genomic SSRs, showing the potentialities of EST-derived microsatellites for resistance studies but also for population genetics approaches.

L’amelioration varietale de Coffea canephora represente un grand defi pour augmenter la productivite de cette espece et assurer un meilleur revenu aux planteurs. Les opportunites sont nombreuses : la diversite genetique de cette espece est bien documentee, les parametres genetiques sont relativement bien etablis pour les principaux caracteres d’interet et les ressources genomiques disponibles s’accumulent. Toutefois, des contraintes sont egalement a considerer : en particulier, l’histoire specifique de la mise en culture et de la selection a conduit a une inegalite des selectionneurs a travers le monde pour l’acces a l’ensemble de la diversite genetique de l’espece. Ainsi, la selection recurrente reciproque (SRR) qui represente une innovation majeure en termes d’utilisation raisonnee des ressources genetiques n’a pu etre menee qu’en Cote d’Ivoire qui seule dispose d’un ensemble complet et reference des ressources genetiques de base de C. canephora. Cette strategie est adaptee a une sortie varietale sous la forme de semences hybrides, plus adaptees a une diffusion de masse que les boutures clonales. En dehors de la Cote d’Ivoire, une selection massale clonale sur des populations en recombinaison plus ou moins bien decrites reste souvent l’axe des programmes de creation varietale. Par ailleurs, le genome de C. canephora est sur le point d’etre sequence et les ressources genomiques sont maintenant suffisantes pour venir en appui des programmes de selection. Les choix strategiques qui permettront d’utiliser au mieux ces ressources au service de l’amelioration genetique doivent etre l’objet d’une reflexion approfondie, tenant compte de l’experience acquise pour d’autres plantes : les cles de ces choix sont discutees.

Background and Aims The production of triploid banana and plantain (Musa spp.) cultivars with improved characteristics (e.g. greater disease resistance or higher yield), while still preserving the main features of current popular cultivars (e.g. taste and cooking quality), remains a major challenge for Musa breeders. In this regard, breeders require a sound knowledge of the lineage of the current sterile triploid cultivars, to select diploid parents that are able to transmit desirable traits, together with a breeding strategy ensuring final triploidization and sterility. Highly polymorphic single sequence repeats (SSRs) are valuable markers for investigating phylogenetic relationships. Methods Here, the allelic distribution of each of 22 SSR loci across 561 Musa accessions is analysed. Key Results and ConclusionsWe determine the closest diploid progenitors of the triploid 'Cavendish' and 'Gros Michel' subgroups, valuable information for breeding programmes. Nevertheless, in establishing the likely monoclonal origin of the main edible triploid banana subgroups (i.e. 'Cavendish', 'Plantain' and 'Mutika- Lujugira'), we postulated that the huge phenotypic diversity observed within these subgroups did not result from gamete recombination, but rather from epigenetic regulations. This emphasizes the need to investigate the regulatory mechanisms of genome expression on a unique model in the plant kingdom. We also propose experimental standards to compare additional and independent genotyping data for reference. (Resume d'auteur)

Coffea canephora Pierre ex Frohener is a perennial plant originated from Africa. Two main groups, Guinean and Congolese, have already been identified within this species. They correspond to main refugia in western and central Africa. In this paper we present the analysis of a region that has not yet been studied, Uganda. Two wild, one feral (once cultivated but abandoned for many years), and two cultivated populations of C. canephora from Uganda were evaluated using 24 microsatellite markers. Basic diversity, dissimilarity and genetic distances between individuals, genetic differentiation between populations, and structure within populations were analysed. Expected heterozygosity was high for wild compartments (0.48 to 0.54) and for cultivated and feral ones (0.57 to 0.59), with the number of private alleles ranging from 12 for cultivated genotypes to 37 for a wild compartment. The Ugandan samples show significant population structuring. We compared the Ugandan populations with a representative sample of known genetic diversity groups within the species using 18 markers. Coffea canephora of Ugandan origin was found to be genetically different from previously identified diversity groups, implying that it forms another diversity group within the species. Given its large distribution and extremely recent domestication, C. canephora can be used to understand the effect of refugia colonization on genetic diversity.

Background A reciprocal recurrent selection program has been under way for the Coffea canephora coffee tree for approximately thirty years in the Ivory Coast. Association genetics would help to speed up this program by more rapidly selecting zones of interest in the genome. However, prior to any such studies, the linkage disequilibrium (LD) needs to be assessed between the markers on the genome. These data are essential for guiding association studies. Results This article describes the first results of an LD assessment in a coffee tree species. Guinean and Congolese breeding populations of C. canephora have been used for this work, with the goal of identifying ways of using these populations in association genetics. We identified changes in the LD along the genome within the different C. canephora diversity groups. In the different diversity groups studied, the LD was variable. Some diversity groups displayed disequilibria over long distances (up to 25 cM), whereas others had disequilibria not exceeding 1 cM. We also discovered a fine structure within the Guinean group. Conclusions Given these results, association studies can be used within the species C. canephora. The coffee recurrent selection scheme being implemented in the Ivory Coast can thus be optimized. Lastly, our results could be used to improve C. arabica because one of its parents is closely related to C. canephora.

Coffea canephora breeding requires combining sustainable productivity with improved technological and cup quality characteristics. Beverage quality is a complex and subjective trait, and breeding for this trait is time consuming and depends on knowledge of the genetics of its components. A highly variable C. canephora progeny resulting from an intraspecific cross was assessed for 63 traits over 5 years. To identify quantitative trait loci (QTLs) controlling agronomic, technological, and quality-related traits, a genetic map comprising 236 molecular markers was constructed, and composite interval mapping was performed. Beverage quality was evaluated in relation to biochemical and cup tasting traits. QTLs were identified for almost half of the traits evaluated, with effects ranging from 6% to 80% of phenotypic variation. Most of them present a consistent detection over years. The strongest QTLs explained a high percentage of the variation for yield in 2006 (34% to 57%), bean size (25% to 35%), content of chlorogenic acids (22% to 35%), sucrose and trigonelline content (29% to 81%), and acidity and bitterness of coffee beverages (30% to 55%). Regions of the C. canephora genome influencing beverage quality were identified. Five QTL zones were co-localized with candidate genes related to the biosynthesis of the analyzed traits: two genes coding for caffeine biosynthesis, one gene implicated in the biosynthesis of chlorogenic acids, and two genes implicated in sugar metabolism. This is one of the first studies on the identification of QTLs combining agronomic and quality traits in coffee. The high variability of quality traits within C. canephora and the presence of consistent QTLs offer breeders a promising tool to improve coffee cup quality.

La présente étude montre la transférabilité de marqueurs microsatellites développés sur les deux espèces de caféiers cultivées (Coffea arabica L. et C. canephora Pierre ex Froehn.) à 15 espèces représentant les principaux groupes précédemment identifiés du genre Coffea. L'évaluation de la diversité et des ressources génétiques disponibles au sein du genre Coffea et le développement de marqueurs moléculaires transférables d'une espèce à l'autre sont des étapes importantes pour l'amélioration de ces deux espèces. Nous avons travaillé sur 15 espèces avec 60 marqueurs microsatellites développés suivant différentes méthodologies (banques enrichies en microsatellites, banques BAC, séquences de gènes). Nous avons plus particulièrement analysé quatre espèces d'intérêt en commerce ou en amélioration. Nos résultats établissent que les microsatellites sont hautement transférables dans le genre Coffea. Nous mettons en évidence l'important réservoir de diversité pour l'amélioration que constituent les espèces sauvages de ce genre. Enfin nous discutons des implications pour de futures études de cartographie comparée et l'amélioration des deux espèces cultivées.