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In the 20th century, agriculture has experienced major gains in productivity via homogenization and intensive use of input, two key components of the dominant model of agriculture in developed countries. This model is jeopardized by the awareness of rapid global change, increased environmental stochasticity and the need for greater sustainability of agriculture. A new paradigm is emerging, in which biodiversity and the mechanisms underlying its dynamics are considered assets for a sustainable agriculture relying more on ecological functions within agroecosystems. Crop genetic diversity should play an essential role in this context, as a key element contributing to agriculture multi-functionality and to the resilience of agroecosystems under rapid climate change and decreased chemical inputs. However, the use of genetic diversity within agroecosystems faces ecological, socio-economic, organizational and regulatory challenges.

The main goal of the project is to better evaluate the possible roles of within-crop genetic diversity to reinforce the multi- functionality and resilience of cropping systems under global change. WHEATAMIX focuses on a major cereal, wheat, in a central area of production, the Paris basin. WHEATAMIX develops a highly multidisciplinary approach involving geneticists, agronomists, ecophysiologists, ecologists, economists, and management scientists, as well as key stakeholders (“Chambres d‟Agriculture”, farmers).

It is structured in four complementary work-packages:

• WP1 will characterise key morphological/ecophysiological traits and genetic variability of wheat genotypes. We will examine the plastic response of these traits to plant-plant interactions and test how trait complementarity affects the performance of wheat genotypes in blends through experiments and modelling.
• WP2 will quantify multiple ecosystem services provided by variety diversity within wheat fields: yield (including grain quality) and its stability, regulation of foliar diseases, insect pest and weed biocontrol, maintenance of soil fertility, along with biodiversity conservation. We will analyse trade-offs and synergies among ecosystem services, as well as links between particular baskets of services and bundles of traits of varieties.
• WP3 will study the techno-economic interest of blends and associated baskets of services for -and their acceptability by- key stakeholders. We will explore the organisational and economic bases of blend choice by the wheat chain (from seed companies to millers), with a focus on the Paris basin. Existing lock-in to the use of associations of wheat varieties will be analysed.

These 3 WPs will use common, complementary experimental approaches: i) individual plant phenotyping to characterize traits and their plasticity for 50 wheat varieties; ii) a main diversity experiment (65 100m2 wheat plots with 1, 2, 4 or 8 varieties, under low input) to quantify variety diversity effect on ecosystem services; iii) replicates of the same diversity experiment in 5 sites across France using smaller (7m2) plots, under low and high inputs, to test the robustness of wheat diversity under a wide range of environmental conditions; iv) a network of 50 farms, encompassing agro-climatic variability in the Paris basin, to compare the ecological and techno-economic performance of blends with that of monocultures, in direct link with key stakeholders.

• WP4 will combine results from WP1-3 and mobilize key stakeholders to build scenarios of the development of wheat variety blends in the Paris Basin considering various future climatic and economic contexts. Opportunities offered by and impacts of the introduction of wheat variety blends in the Paris production basin will be assessed on the basis of these scenarios. A strategy for the dissemination of project results will also be implemented.