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International audience; Germplasm collections of cultivated plants constitute the source for further genetic progress and gained interest with approaches for tracking allelic variants associated to phenotypic variations within core collections. ln order to explore the structure of genetic variation in pepper (Capsicum spp.) and to select core-collections maximizing the genetic and the phenotypic diversity, a pepper collection including 1352 non redundant accessions from Il Capsicum species from 89 different countries was genotyped using 28 microsatellite (SSR) markers spanning the whole genome. Model-based analysis structured the collection into 6 clusters, with 3 clusters separating the main species complexes, including cultivated species and wild relatives, according to botanic classification (C. frutescens/C. chinense, C. baccatum, C. pubescens), and 3 additional clusters for C. annuum. The relationships between the cultivated C. annuum species and the wild relative (C. annnuum var glabriusculum) was refined. The 3 C. annuum clusters were significantly distinct for plant and fruit descriptors corresponding to cultivar types, showing that the genetic structuration of this cultivated species was strongly impacted by the long term hurnan selection of landraces in prirnary as weil as secondary diversification centres. We settled nested core-collections of 8, 16,32, 64 and 128 C annuum accessions capturing from 37% to 90% of the genetic diversity for further sequencing efforts and establishment of high through put genotyping assays. By compiling phenotypic and genotypic data, a larger core-collection of332 accessions was established, capturing 97% of the C. annuum genetic and phenotypic diversity for further genetic association studies

Parmi les Solanacées maraîchères, le piment et la tomate sont confrontés aux attaques de nombreux agents pathogènes, dont Phytophthora capsici et Phytophthora infestans. Des gènes majeurs de résistance ont été identifiés chez la tomate vis-à-vis de P. infestans, et sont fréquemment contournés par des populations virulentes. La résistance du piment à l’égard de P. capsici est conférée par des locus à effet quantitatif (QTL). Pour exploiter efficacement ces résistances quantitatives en sélection variétale, il est nécessaire d’évaluer leur spectre d’action pour prédire leur durabilité. Cette démarche nécessite une bonne connaissance de la diversité des populations pathogènes et de leurs capacités évolutives. La constitution de core-collections représentatives de la diversité intraspécifique de Phytophthora pourrait constituer un outil particulièrement utile pour évaluer a priori la durabilité des résistances variétales. Les résultats des recherches menées à l’INRA révèlent les limites de cette stratégie : elle est utilisable dans un contexte local, exige une bonne connaissance des populations d’agents pathogènes, dépend largement des propriétés épidémiologiques des espèces étudiées, et repose sur la mise en place de protocoles éprouvés de conservation des souches., Among Solanaceous crops, pepper and tomato are damaged by numerous pathogens, including Phytophthora capsici and Phytophthora infestans. Major genes have been identified in tomato to confer resistance against P. infestans, which were rapidly overcome by virulent populations. Pepper resistance towards P. capsici is provided by several quantitative trait loci (QTLs). Efficient exploitation of these polygenic resistance sources in plant breeding requires a good evaluation of their spectrum and durability. This implies a precise knowledge of the genetic and pathogenic diversity of pathogen populations and their adaptive potential. In this context, the establishment of core-collections that would reflect the overall intraspecific diversity of Phytophthora spp. would be useful to assess the a priori durability of resistance sources. The results of the research conducted at INRA reveal the limitations of such a strategy: it may be efficiently developed only locally, requires more knowledge on the structure and epidemiological characteristics of natural pathogen populations, and mainly relies on robust strain storage protocols.

Articles correspondant à plusieurs colloques organisés dans le cadre des séminaires du CTPS en 2012.; National audience; Among Solanaceous crops, pepper and tomato are damaged by numerous pathogens, including Phytophthora capsici and Phytophthora infestans. Major genes have been identified in tomato to confer resistance against P. infestans, which were rapidly overcome by virulent populations. Pepper resistance towards P. capsici is provided by several quantitative trait loci (QTLs). Efficient exploitation of these polygenic resistance sources in plant breeding requires a good evaluation of their spectrum and durability. This implies a precise knowledge of the genetic and pathogenic diversity of pathogen populations and their adaptive potential. In this context, the establishment of core-collections that would reflect the overall intraspecific diversity of Phytophthora spp. would be useful to assess the a priori durability of resistance sources. The results of the research conducted at INRA reveal the limitations of such a strategy: it may be efficiently developed only locally, requires more knowledge on the structure and epidemiological characteristics of natural pathogen populations, and mainly relies on robust strain storage protocols.; Parmi les Solanacées maraîchères, le piment et la tomate sont confrontés aux attaques de nombreux agents pathogènes, dont Phytophthora capsici et Phytophthora infestans. Des gènes majeurs de résistance ont été identifiés chez la tomate vis-à-vis de P. infestans, et sont fréquemment contournés par des populations virulentes. La résistance du piment à l’égard de P. capsici est conférée par des locus à effet quantitatif (QTL). Pour exploiter efficacement ces résistances quantitatives en sélection variétale, il est nécessaire d’évaluer leur spectre d’action pour prédire leur durabilité. Cette démarche nécessite une bonne connaissance de la diversité des populations pathogènes et de leurs capacités évolutives. La constitution de core-collections représentatives de la diversité intraspécifique de Phytophthora pourrait constituer un outil particulièrement utile pour évaluer a priori la durabilité des résistances variétales. Les résultats des recherches menées à l’INRA révèlent les limites de cette stratégie : elle est utilisable dans un contexte local, exige une bonne connaissance des populations d’agents pathogènes, dépend largement des propriétés épidémiologiques des espèces étudiées, et repose sur la mise en place de protocoles éprouvés de conservation des souches.

National audience; Oomycetes form a diverse group of fungus-like eukaryotic microorganisms that include saprophytes as weil as pathogens of animais and some of the most devastating pathogens of dicotyledonous plants. Among them, few species of the genus Phytophthora, such as P. capsici and P. infestons cause enormous economic da mage on Solanaceous crops. Major genes have been identified in tomato to confer resistance against P. infestons, but were rapidly overcome by virulent populations: Pepper resistance towards P. capsici is provided by several quantitative trait loci (QTls). Efficient exploitatio-n of such polygenic resistance sources in plant breeding programs requires a good evaluation of their spectrum and durability. This requires a precise knowledge of the diversity of pathogen populations (with a focus on virulence, aggressiveness and host range) and some of their adaptive traits, such as changes in virulence or adaptation to prevalent cultivars. Theoretically, the use of Phytophthora corecollections reflecting the overall intraspecific diversity would help to assess the a priori durability of resistance sources. We initiated a study to evaluate the potential sustainability of polygenic pepper and tomato resistances to Phytophthora. It implied i) to estimate the diversity of P. infestans and P. caps ici collections and their evolution over time; ii) to develop diverse quantitative and qualitative pathogenic assays to identify the various components underlying polygenic resistances. Collections included isolates from various geographic origins. Genetic diversity was investigated using a combination of neutral markers and genes under positive selection. First results on P. capsici reveal significant variations in the structure and dynamics of regional populations, and suggest that P. caps ici core-collections may be of local interest. We also showed that P. infestons populations are diverse but structured. Hence, strains isolated on tomato or potato differ at the genotypic and phenotypic levels. The use of P. infestons core-collections in breeding programs therefore requires gaining knowledge on the structure and epidemiological characteristics of natural pathogen populations collected on tomato.

International audience

International audience

International audience

Oomycetes form a diverse group of fungus-like eukaryotic microorganisms that include saprophytes as weil as pathogens of animais and some of the most devastating pathogens of dicotyledonous plants. Among them, few species of the genus Phytophthora, such as P. capsici and P. infestons cause enormous economic da mage on Solanaceous crops. Major genes have been identified in tomato to confer resistance against P. infestons, but were rapidly overcome by virulent populations: Pepper resistance towards P. capsici is provided by several quantitative trait loci (QTls). Efficient exploitatio-n of such polygenic resistance sources in plant breeding programs requires a good evaluation of their spectrum and durability. This requires a precise knowledge of the diversity of pathogen populations (with a focus on virulence, aggressiveness and host range) and some of their adaptive traits, such as changes in virulence or adaptation to prevalent cultivars. Theoretically, the use of Phytophthora corecollections reflecting the overall intraspecific diversity would help to assess the a priori durability of resistance sources.[br/][br/] We initiated a study to evaluate the potential sustainability of polygenic pepper and tomato resistances to Phytophthora. It implied i) to estimate the diversity of P. infestans and P. caps ici collections and their evolution over time; ii) to develop diverse quantitative and qualitative pathogenic assays to identify the various components underlying polygenic resistances. Collections included isolates from various geographic origins. Genetic diversity was investigated using a combination of neutral markers and genes under positive selection. First results on P. capsici reveal significant variations in the structure and dynamics of regional populations, and suggest that P. caps ici core-collections may be of local interest. We also showed that P. infestons populations are diverse but structured. Hence, strains isolated on tomato or potato differ at the genotypic and phenotypic levels. The use of P. infestons core-collections in breeding programs therefore requires gaining knowledge on the structure and epidemiological characteristics of natural pathogen populations collected on tomato.

International audience