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Additional file 6: S3 Text. Generation of a new repertoire of small secreted proteins considered as candidate effectors.

Additional file 2: Table S1. Results of the mapping parameters tested for distinguishing between reads from L. maculans and L. biglobosa. (PDF 37 kb)

Additional file 16: S4 Text. Comparison between the v1 and v2 versions of gene model annotations.

Additional file 4: S2 Text. Reproducibility between replicates.

Summary Evolutionary processes during plant polyploidization and speciation have led to extensive presence-absence variation (PAV) in crop genomes, and there is increasing evidence that PAV associates with important traits. Today, high-resolution genetic analysis in major crops frequently implements simple, cost-effective, high-throughput genotyping from single nucleotide polymorphism (SNP) hybridization arrays; however, these are normally not designed to distinguish PAV from failed SNP calls caused by hybridization artefacts. Here, we describe a strategy to recover valuable information from single nucleotide absence polymorphisms (SNaPs) by population-based quality filtering of SNP hybridization data to distinguish patterns associated with genuine deletions from those caused by technical failures. We reveal that including SNaPs in genetic analyses elucidate segregation of small to large-scale structural variants in nested association mapping populations of oilseed rape (Brassica napus), a recent polyploid crop with widespread structural variation. Including SNaP markers in genomewide association studies identified numerous quantitative trait loci, invisible using SNP markers alone, for resistance to two major fungal diseases of oilseed rape, Sclerotinia stem rot and blackleg disease. Our results indicate that PAV has a strong influence on quantitative disease resistance in B. napus and that SNaP analysis using cost-effective SNP array data can provide extensive added value from missing data. This strategy might also be applicable for improving the precision of genetic mapping in many important crop species.

Quantitative resistance has gained interest in plant breeding for pathogen control in low-input cropping systems. Although quantitative resistance frequently has only a partial effect and is difficult to select, it is considered more durable than major resistance (R) genes. With the exponential development of molecular markers over the past 20 years, resistance QTL have been more accurately detected and better integrated into breeding strategies for resistant varieties with increased potential for durability. This review summarizes current knowledge on the genetic inheritance, molecular basis, and durability of quantitative resistance. Based on this knowledge, we discuss how strategies that combine major R genes and QTL in crops can maintain the effectiveness of plant resistance to pathogens. Combining resistance QTL with complementary modes of action appears to be an interesting strategy for breeding effective and potentially durable resistance. Combining quantitative resistance with major R genes has proven to be a valuable approach for extending the effectiveness of major genes. In the plant genomics era, improved tools and methods are becoming available to better integrate quantitative resistance into breeding strategies. Nevertheless, optimal combinations of resistance loci will still have to be identified to preserve resistance effectiveness over time for durable crop protection.

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Session 1 : Interactions Moléculaires. Poster n°1.16Session 1 : Interactions Moléculaires. Poster n°1.16; absent

La compréhension du processus d’adaptation des populations de parasites à leur plante-hôte est une question fondamentale en écologie évolutive. C’est également un enjeu majeur de recherche finalisée qui a des retombées pour la protection des cultures. L’oomycète Plasmopara viticola, agent causal du mildiou de la vigne, attaque les espèces du genre Vitis. Dans un contexte où l’enjeu principal des programmes d’amélioration est la durabilité des résistances, des connaissances nouvelles sur l’écologie et l’évolution de l'interaction entre le parasite et son hôte sont nécessaires afin d’évaluer le potentiel du mildiou à surmonter ces résistances. Dans ma thèse, je me suis intéressée au rôle de la plante-hôte comme facteur d’évolution des populations de mildiou, en posant cette question à différentes échelles évolutives : (i) dans le bassin d’origine du pathogène (Amérique du Nord), j’ai cherché à évaluer le degré de spécialisation du parasite sur sa gamme d’hôtes sauvages et cultivés; (ii) en Europe, où le mildiou de la vigne a été introduit récemment, j’ai étudié l’évolution des populations de mildiou soumis à la pression de sélection des résistances des nouvelles variétés de vigne. Pour comprendre la spécialisation plante-hôte dans ce pathosystème où plusieurs espèces cryptiques ont été identifiées, nous avons réalisé des tests d’inoculations croisées entre espèces hôtes (Vitis spp.) et agent pathogène (P. viticola). Les données phénotypiques et morphologiques apportent les preuves d’une spécialisation plante-hôte au sein des populations de P. viticola : les espèces A et D de mildiou sont spécialisées sur leur plante-hôte, tandis que le processus de spécialisation est en cours pour les espèces B et C. Même si aucune différenciation génétique n’a été montrée au sein de l’espèce C, il existe deux groupes distincts au sein de l’espèce B. Les isolats du compartiment cultivé sont en moyenne plus agressifs que les isolats issus des vignes sauvages, indiquant une adaptation des isolats cultivés sur leur plante hôte. A partir d’un large échantillonnage, nous avons étudié la distribution des espèces de mildiou sur leurs plantes-hôtes sauvages et cultivées. Ce travail a permis d’identifier une nouvelle espèce cryptique et a confirmé la spécialisation plante-hôte. En Europe, nos résultats montrent que le déploiement limité de variétés à résistantes partielles a conduit à des modifications des populations de mildiou: apparition d’isolats virulents (i.e. contournant un QTL majeur de résistance), et augmentation de l’agressivité sur Vitis vinifera. Dans le but de comprendre les mécanismes à l’origine de la spécialisation et du contournement des résistances, nous nous sommes intéressés au répertoire d’effecteurs du parasite. Une centaine d’effecteurs candidats ont été identifiés en utilisant les données disponibles sur le génome de P. viticola. L’analyse du polymorphisme de 32 candidats sur une sélection d’isolats montre que trois d’entre eux évoluent sous sélection positive. Ces résultats soulignent l’importance de la plante-hôte comme facteur de diversification des populations de l’agent pathogène et révèlent que le mildiou s’adapte rapidement aux résistances de la vigne. Il est désormais nécessaire de mieux appréhender le déploiement des résistances de la vigne afin qu’elles puissent être durables., Understanding the process of adaptation of parasite populations to their host-plant is a key issue in evolutionary ecology. It is also a major subject in applied research that has implications for crop protection. The oomycete Plasmopara viticola, the causal agent of downy mildew, attacks the species of the Vitis genus. In a context where the main concern of the breeding programs is the durability of resistance, new knowledge about the ecology and evolution of the interaction between parasite and host is needed in order to evaluate the potential of downy mildew to overcome the resistance. In my thesis, I addressed the role of the host-plant as an evolutionary factor for downy mildew populations, by asking this question at two different evolutionary scales: (i) in the pathogen region of origin (North America) I assessed the degree of specialization of the parasite on its wild and cultivated host range (ii) in Europe, where downy mildew has been introduced recently, I studied the evolution of downy mildew populations subject to the selection pressure imposed by resistant grapevine varieties. To understand the host-plant specialization in this pathosystem, where several cryptic species have been identified, we performed cross inoculations between different host (Vitis spp.) and pathogen (P. viticola) species. Morphological and phenotypic data provide evidence of host-plant specialization in P. viticola populations: downy mildew species A and D are specialized on their host-plant, while the specialization process is ongoing for species B and C. Although no genetic differentiation has been shown inside species C, there are two distinct groups within species B. Isolates from the cultivated compartment are on average more aggressive than isolates from wild vines, indicating an adaptation of isolates growing on cultivated host-plants. Finally, a large-scale study of the distribution of downy mildew species on both their wild and cultivated host-plants resulted in the identification of a new cryptic species and confirmed the host-plant specialization. In Europe, our results show that the limited deployment of resistant varieties has led to changes in downy mildew populations: emergence of virulent isolates (i.e. breakdown of a major QTL for resistance), and increased aggressiveness on Vitis vinifera. In order to understand the mechanisms at the origin of specialization and resistance breakdown, we examined the parasite’s effector repertoire. Over one hundred effector candidates were identified using available data on the P. viticola genome. The polymorphism of 32 candidate genes revealed that three of them evolve under positive selection. Our results reveal the strong ability of downy mildew to adapt to its host plant and to plant resistance. They should be taken into account when devising strategies for the deployment of grapevine resistances in order to guarantee their durability.