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International audience; The objective of this work was to evaluate the resistance of 30 Chilean potato landraces to natural infection by Phytophthora infestans during two growing seasons in Southern Chile. Control cultivars were 'Desiree', which has moderate susceptibility to late blight, and 'Karu', which is characterized by moderate resistance to the disease. The response of the potato landraces to late blight infection was assessed weekly by scoring the percentage of foliage destruction during the growing season. Subsequently, the relative area under the disease progress curve (AUDPCr) was calculated. A wide response variation was observed among the landraces during the occurrence of late blight. The comparative analysis of the AUDPCr showed that three landraces achieved high resistance to the disease (low AUDPCr values). These were UCT-34Cor (0.05), UCT-26Ach (0.06) and UCT-27Mu (0.10). Most of the potato landraces were classified into the range moderately resistant to moderately susceptible. The estimated values of heritabilities of the means were moderate to high for the joint analysis of the two years tested (0.65). The wide range of AUDPCr observed within potato landraces suggests the presence of partial resistance in response to the complex virulence pattern of the P. infestans populations present in Southern Chile.

In order to investigate further the interest of using the Chilean gene pool in potato breeding programmes, the genetic diversity and population structure of a collection ofSolanum tuberosumL. genotypes including 350 worldwide varieties or breeders' lines (referred to as the modern group) and 30 Chiloé Island landraces were examined using simple sequence repeat markers. The close genetic proximity of the Chiloé Island landraces to the modern group was confirmed using several structure analysis methods: principal coordinate analysis; hierarchical clustering analysis; analysis of molecular variance; Bayesian model-based clustering analysis. The latter analysis, in particular, revealed no clear genetic structure between the modern group and the Chiloé Island landraces. The Chiloé Island germplasm appears to represent an interesting gene pool that could be exploited in potato breeding programmes using an association mapping approach.

International audience; The role played by whole-genome duplication (WGD) in evolution and adaptation is particularly well illustrated in allopolyploids, where WGD is concomitant with interspecific hybridization. This Genome Shock', usually accompanied by structural and functional modifications, has been associated with the activation of transposable elements (TEs). However, the impact of allopolyploidy on TEs has been studied in only a few polyploid species, and not in Brassica, which has been marked by recurrent polyploidy events. Here, we developed sequence-specific amplification polymorphism (SSAP) markers for three contrasting TEs, and compared profiles between resynthesized Brassica napus allotetraploids and their diploid Brassica progenitors. To evaluate restructuring at TE insertion sites, we scored changes in SSAP profiles and analysed a large set of differentially amplified SSAP bands. No massive structural changes associated with the three TEs surveyed were detected. However, several transposition events, specific to the youngest TE originating from the B.oleracea genome, were identified. Our study supports the hypothesis that TE responses to allopolyploidy are highly specific. The changes observed in SSAP profiles lead us to hypothesize that they may partly result from changes in DNA methylation, questioning the role of epigenetics during the formation of a new allopolyploid genome.

Background Allopolyploidy is a preeminent process in plant evolution that results from the merger of distinct genomes in a common nucleus via inter-specific hybridization. Allopolyploid formation is usually related to genome-wide structural and functional changes though the underlying mechanisms operating during this "genomic shock" still remain poorly known. The aim of the present study was to investigate the modifications occurring at the proteomic level following an allopolyploidization event and to determine whether these changes are related to functional properties of the proteins. In a previous report, we applied comparative proteomics to synthetic amphiploids of Brassica napus and to its diploid progenitors B. rapa and B. oleracea. Although several hundred polypeptides displayed additivity (i.e. mid-parent values) in the amphiploids, many of them showed non-additivity. Here, we report the in silico functional characterization of the "non-additive" proteins (the ones with a non-additive pattern of regulation) in synthetic B. napus. Results The complete set of non-additive proteins (335 in the stem and 205 in the root), as well as a subset of additive polypeptides (200 per organ), was identified by mass spectrometry. Several protein isoforms were found, and most of them (~55%) displayed "different" or "opposite" patterns of regulation in the amphiploids, i.e. isoforms of the same protein showing both up-regulation and down-regulation in the synthetic B. napus compared to the mid-parent value. Components of protein complexes were identified of which ~50% also displayed "different" or "opposite" patterns of regulation in the allotetraploids. In silico functional categorization of the identified proteins was carried out, and showed that neither functional category nor metabolic pathway were systematically affected by non-additivity in the synthetic amphiploids. In addition, no subcellular compartment was found to be over- or under-represented among the proteins displaying non-additive values in the allopolyploids. Conclusion Protein identification showed that functionally related polypeptides (isoforms and complex subunits) could be differentially regulated in synthetic B. napus in comparison to its diploid progenitors while such proteins are usually expected to display co-regulation. The genetic redundancy within an allopolyploid could explain why functionally related proteins could display imbalanced levels of expression. No functional category, no metabolic pathway and no subcellular localization was found to be over- or under-represented within non-additive polypeptides, suggesting that the differential regulation of gene products was not related to functional properties of the proteins. Thus, at the protein level, there is no evidence for the "genomic shock" expected in neo-polyploids and the overall topology of protein networks and metabolic pathways is conserved in synthetic allotetraploids of B. napus in comparison to its diploid progenitors B. rapa and B. oleracea.

DOI: 10.1002/pmic.200401092; Polyploidization is a major evolutionary process in eukaryotes. In plants, genetic and epigenetic changes occur rapidly after formation of allopolyploids. Hybridization, rather than genome doubling itself, is considered as the main cause for the resulting differential gene expression. We studied the consequences of genome doubling alone in an autopolyploid model, by comparing two-dimensional gel electrophoresis (2-DE) gels of haploid, diploid, and tetraploid Brassica oleracea cabbages. Two fully homozygous lines, HDEM and RC, as well as two organs, leaf and stem, were studied. For the 558 common spots found present in all the 29 2-DE gels of the experiment, inter-organ and -genotype differences were the major sources of the variation in protein amounts: 41 and 10-13%, respectively. HDEM leaf and stem proteomes were not significantly affected by the ploidy level, since no qualitative variation was detected and since the number of quantitative variations could be due to chance. For RC, no qualitative variations were observed, but a few spots were significantly variable in protein amount. However, the number of inter-ploidy variations was of the same range as the number of intra-ploidy variations. In conclusion, whatever the ploidy level, leaf and stem proteomes remained globally unchanged in both cabbage lines.

International audience; Single-row plots (SRP) are often used in early generation selection. For wheat, in such trials, it has already been demonstrated that inter-plot competition leads to highly biased estimations of grain yield. An experiment including one SRP trial and one reference 6-row-plot trial were conducted over two consecutive years in order to compare two statistical models for correcting competition effects. The neighbourhood covariate model relying on plant height proved to be more efficient than the more general producer-competitor model. It provided significant improvement in yield estimation, slightly greater using height measured at heading than using final height as covariate. Moreover, relative efficiency of selection in SRP when corrected for competition effects always reached about 85% , whatever the intensity of competition. The neighbouring covariate model based on plant height should be used for routine analysis of single-row-plot trials.; Modèles de correction de la compétition inter-génotypique chez le blé. Les parcelles monorang sont souvent utilisées dans les schémas de sélection précoce. Dans de tels dispositifs, il a été montré que la compétition entre parcelles adjacentes introduisait un biais dans l'évaluation du rendement. Afin de comparer l'efficacité de plusieurs modèles pour corriger les effets de la compétition, une expérimentation comprenant un essai constitué de parcelles monorang et un essai de référence constitué de parcelles de 6 rangs a été conduite deux années consécutives. Le modèle incluant la covariable de voisinage utilisant la hauteur des plantes s'est révélé plus efficace que le modèle producteur-compétiteur pour corriger le biais introduit par la compétition dans l'évaluation du rendement en parcelles monorang. La correction effectuée par la covariable est faiblement mais significativement meilleure dans le cas où la hauteur est mesurée à l'épiaison qu'à la récolte. D'autre part, l'efficacité relative de la sélection en parcelles monorang, une fois corrigés les effets de la compétition, atteint toujours 85 % , quelle que soit l'intensité de la compétition. La covariable de voisinage utilisant la hauteur des plantes est proposée pour l'analyse en routine des dispositifs d'essais en parcelles monorang.