PhD Project Proposal: From root to field: unraveling the ecological and genetic bases of genotype interactions to design resilient durum wheat variety mixtures Keywords: Durum wheat, variety mixtures, root architecture, plant-plant interactions, functional ecology, quantitative genetics, QTL, climate resilience, drought stress Abstract: Durum wheat is a key crop in Mediterranean regions, increasingly affected by drought stress due to climate change. This PhD project aims to understand how root system architecture, particularly root branching intensity, shapes interactions between genotypes and determines the performance of durum wheat variety mixtures. By combining functional ecology and quantitative genetics, the project will identify the genetic basis of root traits and develop predictive tools to design more resilient and productive varietal mixtures. Context: Durum wheat plays a critical role in global agricultural systems, particularly in semi-arid regions, due to its adaptability, economic significance, and contribution to food security (Sissons 2016). Like other crops from these regions, durum wheat is already experiencing yield reductions caused by increased temperatures and reduced water availability (Rao 2011). Diversifying durum wheat fields by introducing mixtures of varieties instead of mono-genotypic stands could be a solution to improve resource use efficiency through positive interactions between varieties (Barot et al. 2017). Our group has identified several Quantitative Trait Loci (QTLs) associated with Root Branching Intensity (RBI) in durum wheat (Triticum turgidum ssp. durum). Our preliminary data indicate that these candidate QTLs associate with varietal mixture performance under contrasted environmental conditions, suggesting that RBI genes could be involved in plant-plant interactions and could thus be used as a predictive tool to design varietal mixtures. However, optimizing varietal mixture composition remains a major scientific challenge (Borg et al. 2018; Wuest et al. 2021), primarily because the mechanisms underlying varietal interactions are poorly known. Objective: The overarching objective of this thesis is to use plant-plant interactions to enhance the resilience of durum wheat to adverse abiotic conditions, especially drought. More specifically, we aim to develop a better understanding of how plants interact belowground to design assembly rules for varietal mixtures with optimal composition to face water limitations. Methods: In this PhD project, we will combine functional ecology and quantitative genetics to uncover the genetic determinants of root architectural traits and assess their effect on mixture performance. In contrast to previous trait-based approach, our interdisciplinary approach will allow scale down to the genetic levels, potentially leading to a better understanding of the mechanisms underlying varietal interactions under contrasted resource conditions, and providing direct outputs for plant breeding such as molecular markers that could be used to design climate-resilient and genetically diverse durum wheat varieties. This work will be organized in three major tasks: - Detailed root phenotyping on a panel of 180 durum wheat genotypes, conducted under both controlled conditions and in the field, with a specific focus on root branching. - Genetic analyses (GWAS) to identify the QTLs involved in root system architecture and their interaction with water availability. - Variety mixture experiments under different water availability scenarios to assess agronomic performance and decipher the ecological mechanisms (complementarity, competition) related to root traits. To conduct the experiment, the partners will benefit from the collaboration and the expertise of the "Terrain d'Expérience" experimental platform from UMR CEFE for the greenhouse and the "UE DIASCOPE" form the INRAE for the field experiment. Expected results: The first expected result is a dataset of root traits and root trait plasticity in response to water stress, measured using standardized protocols in a wide range of durum wheat varieties. Such high-quality dataset will fill the gap in the low representation of root traits in currently available crop trait databases (e.g., CropTraits). This dataset will be used to study root trait diversity and trait covariations between the above and belowground compartments, and how these are affected by resource availability, which will be published in the first scientific article. The second result will be a characterization of the genetic architecture of architectural root traits in durum wheat and an exploration of the interaction between these genetic factors and durum wheat growth environment, notably through water availability management. The last result will be the experimental assessment of the benefits of varietal mixtures, especially under low water availability conditions. This work will also validate the effect of RBI QTLs on mixture performance and uncover the ecological mechanisms that underly this effect. In addition to this fundamental knowledge, it will help develop predictive models of mixture performance based on root functional traits and genetic markers, fostering plant breeding innovations for the design of resource-efficient varietal mixtures. References: Barot S, Allard V, Cantarel A, et al (2017) Designing mixtures of varieties for multifunctional agriculture with the help of ecology. A review. Agronomy for Sustainable Development 37:13. https://doi.org/10.1007/s13593-017-0418-x Borg J, Kiær LP, Lecarpentier C, et al (2018) Unfolding the potential of wheat cultivar mixtures: A meta-analysis perspective and identification of knowledge gaps. Field Crops Research 221:298-313. https://doi.org/10.1016/j.fcr.2017.09.006 Rao SC (2011) Challenges and strategies of dryland agriculture. Scientific Publishers Sissons M (2016) Durum wheat chemistry and technology. Academic Press Wuest SE, Peter R, Niklaus PA (2021) Ecological and evolutionary approaches to improving crop variety mixtures. Nature Ecology & Evolution 5:1068-1077. https://doi.org/10.1038/s41559-021-01497-x Funding and Practical Information: Fully funded 3-year doctoral contract, covering salary, experimental costs, travel, and conference participation. Candidate Profile: Required: Master's or Engineering degree in plant sciences, agronomy, ecology, or genetics. Desired Skills: Greenhouse and field experimentation, functional ecology, statistical analysis, plant genetics. Essential Qualities: Autonomy, rigor, and teamwork abilities. Language Requirements: French B2 minimum, English B2 minimum. Application: Application deadline: July 31, 2025 Contract Start Date: Between October 1 and December 1, 2025 Applications (CV, motivation letter, preferred start date, recommendation letter) to be sent to: Florian Fort - florian.fort@cefe.cnrs.fr Germain Montazeaud - germain.montazeaud@inrae.fr Germain Montazeaud (to subscribe/unsubscribe the EvolDir send mail to golding@mcmaster.ca)