Etude de la structuration génétique de populations de Melampsora larici-populina, agent de la rouille du peuplier, à différentes échelles spatiales

Texte intégral accessible uniquement aux membres de l'Université de LorraineSince 25 years, the poplar rust fungus, Melampsora larici-populina, is responsible of the most important phytosanitary problems in poplar cultivation. Direct study of biological characteristics, such as dispersal distances or relative importance of sexual vs. asexual reproduction, is often difficult in such pathogenic fungi. A way to infer these characteristics is the use of molecular markers. Fifteen microsatellite markers were developed in order to perform population genetics studies of M. larici-populina at different spatial scales. At a fine scale (leave, twig, tree, site) a great genotypic diversity was observed, as well as a significant structure at the site and tree scales. At a regional scale, the study of M. larici-populina populations in the Durance River valley corridor revealed the co-occurrence of two epidemics, in the wild and in the cultivated compartment. Furthermore, exchanges from cultivated stands to wild stands were shown. The Long distance migration capacity of M. larici-populina was assessed by studying eight European populations and two populations recently founded in Iceland and Canada. European populations exhibited an isolation by distance pattern, whereas non-European populations appeared to result from a long distance dispersal of a limited number of individuals.L'agent de la rouille du peuplier, Melampsora larici-populina, est l'agent pathogène qui pose le plus de problèmes phytosanitaires dans la populiculture européenne depuis ces 25 dernières années. L'étude directe de caractéristiques biologiques, tels que la distance de dispersion ou l'importance relative de la reproduction sexuée et asexuée, est souvent complexe chez ce type de champignons phytopathogènes. L'apport de l'étude de marqueurs moléculaires peut donc se révéler essentiel dans l'estimation de tels paramètres. Quinze marqueurs microsatellites ont été développés afin de réaliser des études de génétique des populations de M. larici-populina à différentes échelles spatiales. L'étude à l'échelle fine (feuille, rameau, arbre, site) de la diversité a révélé un fort polymorphisme génotypique ainsi qu une structuration significative au niveau site et au niveau arbre. A une échelle régionale, l'étude de populations de M. larici-populina dans le corridor de la vallée de la Durance a permis de montrer la co-occurrence de deux épidémies, dans le compartiment sauvage et dans le compartiment cultivé. De plus, des échanges du compartiment cultivé vers le compartiment sauvage ont été mis en évidence. La capacité de migration de M. larici-populina à longue distance a été évaluée en étudiant huit populations du continent européen et deux populations récemment fondées en Islande et au Canada. Un isolement par la distance entre les populations européennes a été mis en évidence, tandis que les populations non-européennes semblent avoir été fondées par une dispersion à longue distance d'un faible nombre d'individus

Evolution de la résistance aux herbicides chez l’Ambroisie (<em>Ambrosia artemisiifolia</em>) : recherche des déterminismes génétiques et application au diagnostic moléculaire

National audienceCe projet de thèse considère une plante adventice particulièrement problématique : l’Ambroisie à feuilles d’armoise (Ambrosia artemisiifolia), une espèce impactant à la fois la production agricole et la santé publique (pollen très allergisant et allergénique). Les inhibiteurs de l’acétolactate synthase (ALS), une famille d’herbicides, représentent aujourd’hui le levier le plus efficace pour le contrôle de cette adventice dans les parcelles agricoles. Cependant, des résistances à ces herbicides ont été identifiées chez l’Ambroisie, entrainant des échecs de traitements. Les données disponibles montrent la présence de résistance liée à la cible (mutations structurales de l’ALS), mais l’essentiel de la résistance identifiée semble dû à des mécanismes non liés à la cible (modifications de la régulation, ou des effecteurs, du métabolisme secondaire). L’objectif de cette thèse est de caractériser ces mécanismes de résistance en identifiant leurs déterminants génétiques, puis de développer et valider des outils moléculaires permettant un diagnostic rapide des résistances de ce type, et ainsi d’optimiser le contrôle des populations d’Ambroisie au champ. Le projet met en oeuvre une combinaison de techniques allant de la caractérisation biologique de plantes (tests de sensibilité) au déploiement d’approches de transcriptomique (RNA-seq, comparatif entre plantes résistantes et sensibles). Une fois les mutations en cause dans la résistance identifiée, les techniques de séquençage de nouvelle génération seront utilisées pour développer des méthodes moléculaires de diagnostic « à haut débit » de la résistance

Effect of host plant species and insecticides on the evolution of genetic diversity of a crop pest

For agricultural pests capable of attacking different plant species, crop distribution and selection pressure imposed by insecticide use are two key constraints imposed on their evolutionary trajectory. Here, we assessed the contribution of host-based genetic differentiation to the dynamics of resistance alleles to three insecticide modes of action in Myzus persicae. This major aphid pest is infamous for its ability to resist to multiple insecticides. Two distinct samplings were conducted: reference sampling on identified crops and continuous random sampling for 7 years using a suction trap. All aphids were genotyped at 14 microsatellite markers and four insecticide-resistant loci. We analyzed the genetic structure of these populations using an individual-centered approach. Four well-defined genetic clusters were found in the aerial samples, three of which could be linked to specific crops. We found a sharp differentiation between peach and herbaceous individuals. Within the individuals sampled on herbaceous hosts, two distinct genetic clusters were identified, one of which seems to be more strongly associated with tobacco. The fourth group was only found in the aerial samples and display strong genetic difference with other groups. The 4-loci resistance genotypes showed a strong association with the four genetic clusters, indicative of barriers to the spread of insecticide resistances. The 7-year continuous random sampling revealed a rapid turnover in aphid genotypes and associated insecticide resistance patterns. This study highlights the importance of considering landscape-scale population structure to identify the risk of emergence and spread of insecticide resistance for a particular crop

Oak powdery mildew changes growth patterns in its host tree: host tolerance response and potential manipulation of host physiology by the parasite

International audience& Context Parasites can induce strong effects on their host's growth, not only as a result of host resource exploitation (growth loss) but also with a potential adaptive value for host (tolerance response) and themselves (increased transmission). & Aims We assessed these three types of phenotypic changes in oak seedlings infected by powdery mildew. & Methods A manipulative field experiment with three levels of parasite inoculum was designed in order to tease apart infection from genetic effects on oak growth. Seedlings were monitored during 3 years for height growth, phenology and infection. & Results Powdery mildew infection induced both significant growth loss and qualitative changes in plant architecture. The most striking and unexpected change was increased growth polycyclism in infected seedlings. This benefitted both the host as a form of compensation for infection-caused height loss, and the pathogen, by increasing sporulation. & Conclusion The study highlights the effect of parasites in the expression of plant phenotypic traits, such as phenology and ultimately tree architecture. Both host tolerance and par-asitic manipulation may be involved in the observed changes in growth patterns. These results suggest a complex interplay between development and defence in trees and emphasize the need to better assess tolerance mechanisms when considering the defence strategies of trees against pathogens

EHE

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EHEdata

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DATA-EHE-2012

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Host plants and insecticides shape the evolution of genetic and clonal diversity in a major aphid crop pest

International audienceUnderstanding the spatiotemporal dynamics of pesticide resistance at the landscape scale is essential to anticipate the evolution and spread of new resistance phenotypes. In crop mosaics, host plant specialization in pest populations is likely to dampen the spread of pesticide resistance between different crops even in mobile pests such as aphids. Here, we assessed the contribution of host-based genetic differentiation to the dynamics of resistance alleles in Myzus persicae, a major aphid pest which displays several insecticide resistance mechanisms. We obtained a representative sample of aphids from a crop mosaic through a suction trap for 7 years and from various crops as a reference collection. We genotyped these aphids at 14 microsatellite markers and four insecticide-resistant loci, analyzed the genetic structure, and assigned host-based genetic groups from field-collected aphids. Four well-defined genetic clusters were found in aerial samples, three of which with strong association with host-plants. The fourth group was exclusive to aerial samples and highly divergent from the others, suggesting mixture with a closely related taxon of M. persicae associated with unsampled plants. We found a sharp differentiation between individuals from peach and herbaceous plants. Individuals from herbaceous hosts were separated into two genetic clusters, one more strongly associated with tobacco. The 4-loci resistance genotypes showed a strong association with the four genetic clusters, indicative of barriers to the spread of resistance. However, we found a small number of clones with resistant alleles on multiple host-plant species, which may spread insecticide resistance between crops. The 7-year survey revealed a rapid turn-over of aphid genotypes as well as the emergence, frequency increase and persistence of clones with resistance to several families of insecticides. This study highlights the importance of considering landscape-scale population structure to identify the risk of emergence and spread of insecticide resistance for a particular crop

Data-MEC-11-1115

Data-MEC-11-111