White poplar (Populus alba L.) is native to Eurasia and is unexploited for its growth potential and stress-adaptive mechanisms. A better knowledge of its genome will allow for more effective protection and use of critical genetic resources. The main objective of this study was the construction of highly informative P. alba genetic maps. Two genotypes were selected from contrasting natural Italian populations and crossed to generate an F 1 mapping pedigree. Amplified fragment length polymorphism and simple sequence repeat markers were used to genotype 141 F 1 individuals. The pseudo-testcross strategy was applied for linkage analysis. The generated maps showed good overall colinearity to each other and allowed for a complete alignment with the 19 haploid chromosomes of the Populus genome sequence. The locus that determines sex as a morphological trait was positioned on a nonterminal position of LG XIX of the female parent map. Comparison among Populus species revealed differences in the location of the sex locus on LG XIX as well as inconsistencies in the heterogametic sex. The genetic analysis of the sex locus in P. alba provides insights into sex determination in the genus and is useful for the identification of sex-linked markers and the early assessment of plant gender. Furthermore, these genetic maps will greatly facilitate the study of the genomics of Populus and how it can be exploited in applied breeding programs. Communicated by S. González-Martínez Isabella Paolucci and Muriel Gaudet contributed equally to this research. Electronic supplementary material The online version of this article (

Abiotic stresses have considerable negative impact on Mediterranean plant ecosystems and better comprehension of the genetic control of response and adaptation of trees to global changes is urgently needed. The single cell gel electrophoresis (SCGE) assay could be considered a good estimator of DNA damage in an individual eukaryotic cell. This method has been mainly employed in animal tissues, because the plant cell wall represents an obstacle for the extraction of nuclei; moreover, in Mediterranean woody species, especially in the sclerophyll plants, this procedure can be quite difficult because of the presence of sclerenchyma and hardened cells. On the other hand, these plants represent an interesting material to be studied because of the ability of these plants to tolerate abiotic stress. For instance, holm oak (Quercus ilex L.) has been selected as the model plant to identify critical levels of O3 for Southern European forests. Consequently, a quantitative method for the evaluation of cell injury of leaf tissues of this species is required. Optimal conditions for high-yield nuclei isolation were obtained by using protoplast technology and a detailed description of the method is provided and discussed. White poplar (Populus alba L.) was used as an internal control for protoplast isolation. Such a method has not been previously reported in newly fully developed leaves of holm oak. This method combined with SCGE assay represents a new tool for testing the DNA integrity of leaf tissues in higher plants under stress conditions.

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Amplification products of these 13 loci were also generated for T. gallica. These new EST-SSR markers will be useful in genetic characterization of Tamarix, as additional tools for taxonomic clarification, and for studying invasive populations where they are a threat.

Both the negative and positive ecological impact of Tamarix plants is controversial, and thus a more comprehensive understanding is necessary. Tamarisks are invasive in many countries but the inter-specific transferability that characterizes simple sequence repeats (SSRs) could be harnessed to track the spread of specific genotypes or to study invasive populations. Thirteen polymorphic SSR markers, derived from expressed sequence tag (EST), were identified by first screening 26 samples of T. aphylla, T. jordanis, T. nilotica, and T. tetragyna and then 33 unidentified tamarisks from Yotvata, Israel. The mean number of alleles per locus ranged from two to 14 and the mean expected heterozygosity was 0.415. These EST-SSR markers will undoubtedly be useful in the genetic characterization of the genus Tamarix due to their high cross-species transferability which enables the estimation of the genetic diversity among and within different species, that are adapted to the same desert habitat under severe environmental constraints.

Tamarix L. plants are tolerant to extreme environmental conditions and represent a resource for the recovery of marginal areas. The aim of this study is to develop a molecular method for species assignment and to characterize the genetic differentiation of Italian Tamarix populations. Blind sampling was performed and individuals were gathered without any regard for species identity from seven sites in Italy. If possible, flowers for species identification were collected, but 60% of samples remained unidentified. The genotypic profile of 17 microsatellite markers and a Bayesian statistical approach allowed the individuals to split among genetic entities rather than by their species identity. A clear assignment of Tamarix africana Poir. individuals was found, but this was not the case for Tamarix gallica L. and Tamarix canariensis Willd., whose individuals were clustered in a unique group (T. gallica-like). In T. africana, the Bayesian analysis of the genetic structure pointed out the existence of a unique gene pool, whereas according to principal coordinates analysis (PCOA) and F ST values, the populations from Lazio and Sardinia were more differentiated. All the analyses performed showed a differentiation between Sicily and peninsular Southern Italy in the T. gallica-like group. This study is the first to report the characterization of the natural genetic resources of Italian tamarisks and it suggests the absence of genetic differentiation between T. gallica and T. canariensis.Résumé : Les plantes de Tamarix L. sont tolérants à des conditions environnementales extrêmes et représentent une ressource pour la restauration des zones marginales. Le but de cette étude était de développer une méthode moléculaire permettant d'assigner un individu à une espèce et de caractériser la différenciation génétique des populations de Tamarix en Italie. Un échantillonnage au hasard a été réalisé et des individus ont été récoltés à partir de sept sites en Italie, peu importe l'identité des espèces. Lorsque cela était possible, les fleurs permettant d'identifier l'espèce ont été recueillies, mais 60 % des échantillons demeuraient non identifiés. Le profil génotypique de 17 marqueurs microsatellites et une approche statistique bayésienne ont permis de séparer les individus en entités génétiques plutôt que par leur identité en tant qu'espèce. Une assignation claire des individus appartenant à Tamarix africana Poir. a été trouvée, contrairement à Tamarix gallica L. et Tamarix canariensis Willd., dont les individus s'agrégeaient en un seul groupe (apparenté à T. gallica). Chez T. africana, l'analyse bayésienne de la structure génétique a souligné l'existence d'un pool génétique unique, alors que selon l'analyse en coordonnées principales (PCOA) et les valeurs de F ST , les populations de Lazio et de Sardaigne étaient davantage différenciées. Toutes les analyses réalisées ont montré une différenciation du groupe apparenté à T. gallica entre la Sicile et la péninsule de l'Italie du Sud. Cette étude est la première à rapporter la caractéri...

In this study, the genes of the Aux/IAA family were used as functional markers to characterise bud break stages in a white poplar clone. In the first experiment, under greenhouse conditions, the sprouting of repressed sylleptic buds was obtained by pruning the shoot tip during growing season. Buds were collected at 0, 6, 24 and 48 h after pruning for molecular analyses. A decrease in transcript level of IAA4 and IAA8 genes was observed in the first and second bud below the cut after 6 and 24 h, respectively. In the second experiment, bud break of post-dormant proleptic buds was induced by forcing in climatic chamber. The first 6 and the following 6 buds below the apical one were sampled every 48 h during forcing. Anatomical studies were also carried out on buds and plants were equipped with stem and bud radial growth sensors to check their swelling. In both experiments, gene expression patterns showed a decrease and a successive increase in expression of IAA4 and IAA8 genes during bud break. The transient down-regulation of these genes was observed only in buds that formed new branches. Thus, similar molecular mechanisms are involved in bud break of both sylleptic and proleptic buds.

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