Abstract
Cultivar mixtures are increasingly present in the French agricultural landscape, but their adoption rates and performances vary spatially. Understanding the reasons for this variability is important to support and rationalize their adoption. From a theoretical perspective, mixed varieties are an assemblage of genotypes that interact with each other. The study of interactions between genotypes in a plant cover is fundamental to understand the variability in the performance of mixed varieties. Functional ecology has extensively studied plant-plant interactions by describing patterns of association between plant traits (e.g., height, leaf area, root length, etc.) and the productivity of plant communities. From a genetic perspective, plant-plant interactions have been less explored. However, it is essential to decipher the genetic basis of plant interactions to better understand the impact of diversity on the productivity of cultivated communities.In this context, this thesis, structured into four chapters, aims to address four research questions using durum wheat as a model for studying cereals. First, we conduct a retrospective analysis of the evolution of plant interactions since the Green Revolution to understand how plant breeding programs in the 20th century have modified plant interactions. Second, we will assess the potential of mixed varieties to reduce fertilization in the context of agro-ecological transition. Specifically, we will ask: Does the level of resources influence interactions between genotypes and the yield of durum wheat mixed plots? Third, we will analyze whether the way wheat varieties are arranged in a field influences the nature of interactions between genotypes and the performance of genotype mixtures. Finally, in the last part, we focus on the analysis of fungal community traits. These traits are assumed to play an important role in plant performance and plant interactions through nutritional or protective functions against pathogens. However, fungal communities are difficult to describe statistically. In this final section, we propose a method for describing fungal communities and analyze the potential for incorporating fungal communities into a plant breeding program aimed at developing mixed varieties. We will conclude by discussing the implications of these questions for the design of new experiments and the development of new selection schemes.