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Theses

Développement de méthodes d'estimation de l'aptitude au mélange pour la prédiction des performances et la sélection de mélanges variétaux chez le blé tendre, et co-conception d'idéotypes de mélanges adaptés à l'agriculture biologique

Abstract : Cereal variety mixtures have recently known a renewed interest but methods for screening and breeding varieties for mixing ability, or designing mixtures remain poorly developed. It has been shown that the performance in pure stand of a genotype can significantly differ from its performance in mixture, thus making mixture performance difficult to predict. But testing all the possible mixtures turns technically impossible when using large panels of genotypes. Therefore experimental and statistical methods are necessary to identify the genotypes with the best mixing ability, as well as try to predict the best combinations, from the observation of a limited number of mixtures.In a first part, we have reviewed different methods proposed in the literature to study these plant-to-plant interactions, contrasting i) the ones based on mixture performances, producing General and Specific Mixing Ability estimates, from ii) the ones where the performance of each genotype in the mixture is observed, allowing to estimate Producer and Associate effects. We have then proposed a statistical framework based on mixed models to estimate Mixing Ability in incomplete designs. These Mixing Ability models and the Producer-Associates model have been applied to a diverse panel of bread winter wheat genotypes observed in different experimental designs, revealing interactions between plants of different genotypes. Then the ability of these designs and models to predict the performance of validation mixtures have been compared. We finally discussed how these methodological frameworks can be applied to screening for mixing ability and the possibility to integrate them in breeding programs.In a second part, we performed a literature survey to propose assembly rules for better combining traits associated to plant interactions, and designing mixture idéotypes that favor the complementarities between varieties. During participatory workshops involving organic farmers, these rules have been validated, invalidated, adapted or implemented, and then used for designing mixture ideotypes that fit farmers’ practices and environments. The designed mixtures based on these rules have been assessed in on-farm trials for agronomic criteria and farmers’ specific requirements. The two complementary approaches of this thesis unleash the potential for developing locally adapted cultivar mixtures.
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Emma Forst. Développement de méthodes d'estimation de l'aptitude au mélange pour la prédiction des performances et la sélection de mélanges variétaux chez le blé tendre, et co-conception d'idéotypes de mélanges adaptés à l'agriculture biologique. Génétique des plantes. Université Paris Saclay (COmUE), 2018. Français. ⟨NNT : 2018SACLS069⟩. ⟨tel-02114929⟩

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