Miscanthus (Miscanthus Andersson) is a perennial grass that is attracting growing interest from the biomaterial industry. Our aim was to compare miscanthus genotypes varying in stem solidness, a measure of degree to which pith fills cavity between the outer walls of the stem, and analyze whether this trait influences the mechanical properties of polypropylene composites reinforced with miscanthus particles. Six contrasting genotypes were chosen from a Miscanthus sinensis population to determine morphological variables, stem solidness, and mechanical properties of polypropylene composites including 30% of milled miscanthus particles of two sizes of 100 < × < 200 μm and 200 < × < 300 μm. Although aboveground biomass of miscanthus was closely related to the aboveground volume of the plant, namely stand volume, a few genotypes showed contrasting aboveground biomass production for similar stand volumes. This generated contrasting ratio between aboveground biomass and stand volume, namely plant‐specific weights, for similar plant volumes. A principal component analysis showed that fully pith‐filled stems, namely solid stems, were explained by a large stand volume and plant‐specific weights as well as small stem cross‐sections. Genotypes showing partially filled stems were taller with larger stem cross‐sections but smaller plant‐specific weights. They revealed high lignin and p‐coumaric acid contents. Compared to neat‐polypropylene, Young's modulus increased significantly by 139% and 134% and tensile strength by 39% and 36% for genotypes with partially filled stems compared to genotypes with fully pith‐filled stems, respectively. This difference in reinforcing capacity was similar to that of two particle sizes (139% and 134% for Young's modulus, 41% and 34% for tensile strength, respectively). A good tensile strength was obtained with large cross‐stem section, plant height and lignin and p‐coumaric acid contents. It decreased with plant‐specific weight, hemicellulose and ferulic acid contents. Wider morphological variations in other progenies or Miscanthus species should be explored further using the techniques reported here.

There is a growing interest in the cultivation of miscanthus on marginal land, but biomass yields are much lower there than on good farming land. Therefore, understanding what causes such instability is of primary interest for breeding later-flowering but stable miscanthus genotypes. Our objectives were to estimate the genetic parameters -genetic variance and genetic heritability- and genetic correlations for flowering-time-related traits in a biparental Miscanthus sinensis diploid population, and to divide the year effect into both age and climate effects using a staggered-start design. The population was established with single plants organized in a staggered-start design and consisted of two genotype groups established twice, in 2014 and 2015, with a total of 159 genotypes and 82 common genotypes between the two groups. All plants were extensively phenotyped for different panicle and anther emergence traits in 2018 and 2019. All traits were delayed by about 20 days in 2019 compared to 2018, which was explained by climatic conditions that occurred before the floral transition, mainly by a 3°C decrease in maximal and minimal temperatures. When dividing the year interaction effect, the genotype × climate interaction was much higher than the genotype × age interaction. The climate effect not only caused a delay in the flowering time but also involved differential genotype behavior through climate × genotype interactions, which increased the corresponding genotype × climate interaction variance compared to the genotype × age interaction variance: the climate effect decreased the genetic parameters for all flowering-time related traits, up to 20 % for broad-sense heritability. Interestingly, all traits responded similarly to the climate effect, excepting the interval between the start of panicle emergence and that of anther appearance, for which the correlation coefficients were lower due to significant climate interactions, compared to genotype × age interactions. Therefore, M. sinensis breeding for flowering-time related traits must be conducted under contrasted climates in order to select more stable genotypes.

There is a growing interest in the cultivation of miscanthus on marginal land, but biomass yields are much lower there than on good farming land. Therefore, understanding what causes such instability is of primary interest for breeding laterowering but stable miscanthus genotypes. Our objectives were to estimate the genetic parameters -genetic variance and genetic heritability-and genetic correlations for owering-time-related traits in a biparental Miscanthus sinensis diploid population, and to divide the year effect into both age and climate effects using a staggered-start design. The population was established with single plants organized in a staggered-start design and consisted of two genotype groups established twice, in 2014 and 2015, with a total of 159 genotypes and 82 common genotypes between the two groups. All plants were extensively phenotyped for different panicle and anther emergence traits in 2018 and 2019. All traits were delayed by about 20 days in 2019 compared to 2018, which was explained by climatic conditions that occurred before the oral transition, mainly by a 3°C decrease in maximal and minimal temperatures. When dividing the year interaction effect, the genotype × climate interaction was much higher than the genotype × age interaction. The climate effect not only caused a delay in the owering time but also involved differential genotype behavior through climate × genotype interactions, which increased the corresponding genotype × climate interaction variance compared to the genotype × age interaction variance: the climate effect decreased the genetic parameters for all owering-time related traits, up to 20 % for broad-sense heritability. Interestingly, all traits responded similarly to the climate effect, excepting the interval between the start of panicle emergence and that of anther appearance, for which the correlation coe cients were lower due to signi cant climate interactions, compared to genotype × age interactions. Therefore, M. sinensis breeding for owering-time related traits must be conducted under contrasted climates in order to select more stable genotypes.