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This thesis defense will take place on Tuesday December 12 at 2:00 pm in the Colette & Josy Bové Amphitheatre, 71 Av. Edouard Bourlaux, 33140, Villenave d'Ornon.
 

Abstract :  Fusarium graminearum is one of the main agents responsible for Fusarium Head Blight, a worldwide disease affecting cereal crops, the presence of which can lead to contamination of grain by chemically stable and harmful mycotoxins. In a context of climate change, it is essential to understand the adaptive capacity of F. graminearum in order to better anticipate the epidemic risk linked to the potential emergence of new adapted isolates. The adaptive potential of a species to environmental change is linked to its genetic evolutionary capacity and the phenotypic plasticity of the individuals in the population.

In particular, phenotypic plasticity makes it possible to respond immediately to changes in the environment. We characterized phenotypic plasticity for mycotoxin production and in vitro growth, between a control condition and a treated condition for four different environments: temperature (E1), oxidative component (E2), water availability (E3) and nitrogen concentration of the medium (E4). We observed that phenotypic plasticity varied between environments, phenotypes and genotypes, suggesting the ubiquitous nature of phenotypic plasticity and its genetic control. Next, the genetic determinism of plasticity was investigated through a population genomics approach using genome-wide association study (GWAS) by whole genome sequencing (WGS). To our knowledge, this is the first GWAS approach applied to toxigenic fungi characterizing phenotypic plasticity implemented to date. We have shown that phenotypic plasticity is under complex genetic determinism, notably through an architecture linked to the epistatic model of phenotypic plasticity, even if the hypothesis of an epigenetic basis remains likely.

In another part, we studied whether the mutation is related to the adaptability of F. graminearum. We carried out an experimental evolution to explore mutational dynamics under selection pressure according to different propagation modes (mycelium and conidiospores). Small differences between the 1st and 19th propagation cycles were observed in strain phenotypes, and very few mutations were found (only for vegetative propagation). Hypotheses linked to insufficient selection pressure or genetic drift were evoked in view of these results.

Taken together, these results lay new foundations for the phenotypic and genetic adaptation of the plant pathogenic fungus F. graminearum to climate change.