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To develop the perennial grass Miscanthus x giganteus as a highly productive crop for biomass production, new varieties need to be bred, and more knowledge about its growth behaviour has to be collected. Our aim was to identify an efficient function for assessing and comparing emergence date and canopy height growth (rate, duration, and final maximal height) of 21 clones of Miscanthus in Northern France. Flow cytometry made it possible to classify the clones into three clusters corresponding to 2x, 3x, and 4x ploidy levels. Three functions, 3-and 4-parameter logistic functions and Gompertz function, were tested to best describe the dynamics of crop emergence and of plant growth. The best functions were used to estimate emergence dynamics (Gompertz function), and growth dynamics (4-parameter logistic). All these traits showed a significant year, clone, and corresponding interaction effects (but not for harvest date). Species and ploidy level explained the clone and clone × year interaction effects. M. x giganteus and M. floridulus clones were among the latest to emerge, and the tallest. M. sinensis clones showed the lowest height and growth rates. Higher final canopy height was correlated to late emergence and high growth rate. These findings could help early selection of interesting clones within M. sinensis populations, in order to breed new inter-species hybrids of giganteus type.

-The European Union recommends the use of lignocellulosic biomass to produce biofuels in order to reduce greenhouse gas emissions. Miscanthus × giganteus, a C 4 perennial and rhizomatous plant, has been identified as a good candidate for biomass production because of its high potential yield, of up to 49 t DM.ha −1 for autumn harvest and 26 t DM.ha −1 for winter harvest, under low input levels. Here, we review current knowledge on the biomass production in Europe of M × giganteus and its two parental species, M. sinensis and M. sacchariflorus, under different stress conditions. This review identifies two key areas where M. giganteus crops could be improved: (i) tolerance to frost during winter or early spring is essential, mainly in Northern Europe, in order to ensure overwintering and protect young shoots following early emergence. Susceptibility to winter frost at temperatures below −3.5• C for rhizomes and −8• C for young shoots of M. × giganteus can lead to significant plant losses and lower yields, and (ii) a good water supply is necessary to ensure good establishment rates and satisfactory biomass production. Reductions of up to 84% in above-ground dry matter production because of a lack of water for the autumn harvest, and up to 26% for the winter harvest have been observed. M. sinensis, which displays greater genetic variability than M. giganteus, will provide the necessary genetic resources for frost and water stress tolerance. It is also necessary to either identify genotypes among M. sinensis species that are able to produce an above-ground biomass yield close to the biomass production of M. giganteus under limited water supplies and/or low temperatures, or to generate new interspecific hybrids of M. giganteus with greater tolerance. Particular attention should be paid to nitrogen response; although no response to nitrogen supply has been observed in M. giganteus, M. sinensis produces higher levels of biomass with nitrogen inputs.Miscanthus / biomass production / chilling temperature / frost / nitrogen supply / water supply / improvement Abbreviations: DM, dry matter; WUE, water-use efficiency; NUE, nitrogen-use efficiency; RUE, radiation-use efficiency

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International audienceThe production of ligno-cellulosic biomass-based composites requires the development of new methodologies to evaluate the reinforcement potential of a given biomass, such as miscanthus studied in the work. Miscanthus stems from thirteen genotypes were broken into elongated fragments and mixed with polypropylene composites in an internal mixer. The aim is to find the best protocol able to discriminate miscanthus genotypes for their reinforcement capability. The following process parameters were optimized in order to maximize the reinforcement effect of the stem fragment filler: mixing parameters (mixing time, rotor speed and chamber temperature), temperature, fragment content, size and length distributions and coupling agent. The relationship between the process parameters and the mechanical properties of composites were analyzed to evaluate the influence of genotype on reinforcement performance, showing the robustness of the protocol in effectively discriminating genotypes according to their reinforcing capacity

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