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To face global warming and fossil fuel depletion crisis, plant biomass will provide a renewable source of energy, materials and chemicals. Accordingly, agriculture will have to adapt not only to avoid competition between food-feed and non-food non-feed uses but also to ensure the economical and environmental sustainability of these productions. In this context, we are developing an integrative strategy merging genetics, breeding, material sciences, energy production, animal nutrition and socio economic analyses to accelerate the development of multipurpose sorghum value chains for both Mediterranean and tropical semi-arid conditions (West Africa). As a first step, new products (biocomposites) and uses (biomethane production) are being developed. Then the plant traits impacting the production and quality of the different end-products and uses are being identified taking advantage of the genetic diversity of sorghum. As a third step, the set-up of these key traits in the plant is being analyzed in order to describe their patterns of development / accumulation, their susceptibility to environmental constraints and provide some insights regarding their molecular determinism. Taking advantage of these functional information, the genomic regions impacting the key traits are being deciphered and used to develop new breeding tools and breeding strategies. In parallel, to maximize the probability to convert scientific results in local impacts, the different stakeholders of the value chains are being mobilized and territorial analyses aiming to assess the relevance of the different value chains are performed.

International audience; Polymer composites prepared with a polymer matrix reinforced by elongated, broken fragments of plant stems can in some cases favorably compete with the same composite reinforced by glass fibers. However, the mechanical properties of the final composite are directly related to the properties of the stem fragments. Cellulose is the main polymer controlling the mechanical strength of these fragments. Two plants will be studied, miscanthus and sorghum. We will show that amount of cellulose in the stem fragments depends on the preparation methods of these fragments. We will report the correlations which exists between the amount of cellulose and its location within the different tissues of the stem and the mechanical properties of the final composite product.

International audience; Composites prepared with whole sorghum stem fragments reinforcing a polyethylene matrix were studied using ten different sorghum genotypes. We first built of a robust protocol ensuring an accurate assessment of composite physical and mechanical properties. It shows that for a given sorghum genotype, the composition of the stem fragments is depending on the size of the fragments. This justifies the need to use a similar stem fragment size for comparing genotypes. During compounding and injection, fragments are broken, to an extend which depends on genotypes. This robust processing protocol shows that there are large differences in the final mechanical properties of the composites depending on the genotype. This is correlated with the histological structure and the biochemical composition of each genotype, showing correlations between the amount of cellulose, hemicellulose and lignin present in the stem fragments with the mechanical properties of the composites, as well as the importance of the location of cellulose (sclerenchym fibers versus parenchym tissues and vessels). We will show the difficulties of working with small, well identified amounts of biological materials when dealing with composite-filler biochemical and structural characteristics which are heavily varying between on position to another along the plant stem. This work is the first step of a plant breeding process for identifying the best sorghum varieties to be used for preparing polymer composites.

International audience; The use of natural lignocellulosic aggregates like wood or plant fibers instead of mineral ones for preparing concrete is hampered by several factors, mainly the facts that natural aggregates are competing with cement for water, that they have lower mechanical properties and that the highly alkaline cement-water mixture is degrading the natural fillers, releasing sugars which are retarding cement hydration. All these three factors are leading to difficulties for preparing such concrete and are strongly decreasing their mechanical resistance. After reviewing the different treatments which have been proposed in literature, we will show that it is possible to prepare plant stem fragment reinforced concrete with suitable mechanical properties with and without pre-treatments when properly taking into account the release of sugars during the cement setting process, the effect of plant genotype and the role of cement composition.

Sorghum is among the world's most important cereals in terms of human and animal nutrition. It is also currently identified as a promising crop to support the emerging bio-economy value chains that include energy production, biomaterials and molecules for food-feed and non-food-feed applications. In this context, the development of varieties adapted to the different end-uses is critical to provide the industries with relevant feedstock. Breeding sorghum for existing and emerging markets requires several steps, from the definition of “Industrial Ideotypes” down to the identification of “Molecular Ideotypes” in order to speed up the breeding process and optimize the genetic gains per unit of time. Firstly, expectations of the industrials in terms of composition and properties of the sorghum biomass for the different applications (“Industrial ideotypes”) have to be defined. Secondly, “Industrial ideotypes” have to be translated in “Biological ideotypes” which refers to the properties of the raw sorghum material in terms of composition and structure. Third, high-throughput phenotyping tools compatibles with genetic analyses and breeding constraints have to be developed. Fourth, strategies to disentangle the genetic determinism of the “Biological Ideotypes” have to be set up. And fifth, relevant breeding schemes able to provide new hybrids and relevant parents have to be initiated. We will illustrate this process through two examples related to the production of sorghum biocomposites and the optimization of sorghum biogas production. For both targets, we will show how, through the use of the sorghum genetic diversity, traits affecting the final product properties were identified. We will then illustrate the efforts that are currently developed to tackle the challenges linked to high-throughput phenotyping. We will finally show how these phenotyping tools are used on diverse association panels and multiparental designs to identify the genomic regions affecting the traits of interest and develop new hybrids and elite parents. Funding acknowledgement: This research is supported through the Biomass For the Future project (funded by ANR) and the BIOSORG project supported by the Agropolis (Labex Agro) and Cariplo foundations.