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Genetic improvement through breeding is one of the key approaches to increasing biomass supply. This paper documents the breeding progress to date for four perennial biomass crops (PBCs) that have high output-input energy ratios: namely Panicum virgatum (switchgrass), species of the genera Miscanthus (miscanthus), Salix (willow) and Populus (poplar). For each crop, we report on the size of germplasm collections, the efforts to date to phenotype and genotype, the diversity available for breeding and on the scale of breeding work as indicated by number of attempted crosses. We also report on the development of faster and more precise breeding using molecular breeding techniques. Poplar is the model tree for genetic studies and is furthest ahead in terms of biological knowledge and genetic resources. Linkage maps, transgenesis and genome editing methods are now being used in commercially focused poplar breeding. These are in development in switchgrass, miscanthus and willow generating large genetic and phenotypic data sets requiring concomitant efforts in informatics to create summaries that can be accessed and used by practical breeders. Cultivars of switchgrass and miscanthus can be seed-based synthetic populations, semihybrids or clones. Willow and poplar cultivars are commercially deployed as clones. At local and regional level, the most advanced cultivars in each crop are at technology readiness levels which could be scaled to planting rates of thousands of hectares per year in about 5 years with existing commercial developers. Investment in further development of better cultivars is subject to current market failure and the long breeding cycles. We conclude that sustained public investment in breeding plays a key role in delivering future mass-scale deployment of PBCs.

Genetic improvement through breeding is one of the key approaches to increasing biomass supply. This paper documents the breeding progress to date for four perennial biomass crops (PBCs) that have high output-input energy ratios: namely Panicum virgatum (switchgrass), species of the genera Miscanthus (miscanthus), Salix (willow) and Populus (poplar). For each crop, we report on the size of germplasm collections, the efforts to date to phenotype and genotype, the diversity available for breeding and on the scale of breeding work as indicated by number of attempted crosses. We also report on the development of faster and more precise breeding using molecular breeding techniques. Poplar is the model tree for genetic studies and is furthest ahead in terms of biological knowledge and genetic resources. Linkage maps, transgenesis and genome editing methods are now being used in commercially focused poplar breeding. These are in development in switchgrass, miscanthus and willow generating large genetic and phenotypic data sets requiring concomitant efforts in informatics to create summaries that can be accessed and used by practical breeders. Cultivars of switchgrass and miscanthus can be seed-based synthetic populations, semihybrids or clones. Willow and poplar cultivars are commercially deployed as clones. At local and regional level, the most advanced cultivars in each crop are at technology readiness levels which could be scaled to planting rates of thousands of hectares per year in about 5 years with existing commercial developers. Investment in further development of better cultivars is subject to current market failure and the long breeding cycles. We conclude that sustained public investment in breeding plays a key role in delivering future mass-scale deployment of PBCs.

Harvest time is an important variable that determines the yield of miscanthus biomass, its possible end uses, and the nutrient offtake from the field. Green harvests result in a higher yield and greater nutrient removal from the field. Brown miscanthus harvests, carried out in late winter or early spring, result in lower yields and a lower nutrient offtake, whereby the harvested biomass is better suited to use in combustion. To look at the long‐term impact of green harvests on miscanthus, this experiment followed the yield development of two miscanthus hybrids subjected to green and brown harvests over a period of seven years at one site in Southern Germany. The standard commercial hybrid Miscanthus × giganteus (Mxg) was compared with a novel late‐ripening Miscanthus sinensis hybrid: Syn55. Average yields of Mxg were 19.9 t ha−1 for green harvests and 13.2 t ha−1 for brown harvests compared to 13.9 and 12.9 t ha−1 for green and brown harvested Syn55, respectively. Yields of Mxg were very different for green and brown harvests; green harvested Mxg had very high nutrient offtake, while brown harvested Mxg had the lowest nutrient offtakes of all treatments. Syn55 showed a less marked difference between green and brown harvests likely due to its tendency to retain its leaves over winter. Syn55 was however not tolerant of a green harvest, with yields of brown harvested stands surpassing the yield of green harvested stands in several years. Although Mxg demonstrated consistently high yields when harvested in October, some signs of yield decline were detected in both hybrids when harvested green, which was due to insufficient carbohydrate relocation. Alternating green and brown harvests are recommended to allow stands to replenish carbohydrate stores and to form a litter layer. [ABSTRACT FROM AUTHOR]

Miscanthus is a promising crop for bioenergy and biorefining in Europe. The improvement of Miscanthus as a crop relies on the creation of new varieties through the hybridization of germplasm collected in the wild with genetic variation and suitable characteristics in terms of resilience, yield and quality of the biomass. Local adaptation has likely shaped genetic variation for these characteristics and is therefore important to quantify. A key biomass quality parameter for biorefining is the ease of conversion of cell wall polysaccharides to monomeric sugars. Thus far, the variability of cell wall related traits in Miscanthus has mostly been explored in accessions from limited genetic backgrounds. Here we analysed the soil and climatic conditions of the original collection sites of 592 Miscanthus genotypes, which form eight distinct genetic groups based on discriminant analysis of principal components of 25,014 single-nucleotide polymorphisms. Our results show that species of the genus Miscanthus grow naturally across a range of soil and climate conditions. Based on a detailed analysis of 49 representative genotypes, we report generally minor differences in cell wall characteristics between different genetic groups and high levels of genetic variation within groups, with less investigated species like M. floridulus showing lower recalcitrance compared to the other genetic groups. The results emphasize that both inter- and intra-specific variation in cell wall characteristics and biomass recalcitrance can be used effectively in Miscanthus breeding programmes, while also reinforcing the importance of considering biomass yield when quantifying overall conversion efficiency. Thus, in addition to reflecting the complexity of the interactions between compositional and structural cell wall features and cell wall recalcitrance to sugar release, our results point to traits that could potentially require attention in breeding programmes targeted at improving the Miscanthus biomass crop. [ABSTRACT FROM AUTHOR]

Climate change and man-made pollution can have a negative impact on the establishment of Miscanthus plants in the field. This is particularly important because biomass can be produced on marginal land without conflicting with food crops. The establishment success depends on the hybrid chosen, the cultivation method, the climatic conditions, and the concentration of pollutants in the soil. There are several ways to increase the survival rate of the plants during the first growing season and after the first winter. One of them is the application of biochar and photodegradable plastic mulch, which can provide a solution for soils polluted with trace elements (TMEs). The aim of this study was to investigate the application of plastic mulch and biochar separately and in combination at the planting stage for two Miscanthus hybrids planted by the rhizome method (TV1) and seedling plugs (GNT43) on soils contaminated with trace metal elements (Pb, Cd, Zn). TV1 seems unsuitable for TME-contaminated field cultivation, as the survival rate was <60% in most treatments studied. The selected treatments did not increase the survival rate. Furthermore, the application of plastic mulch in combination with biochar resulted in a significant reduction of this parameter, regardless of the hybrid studied. The applied agrotechnology did not influence the TME accumulation in the aboveground plant parts in TV1, while Pb and Cd in GNT43 showed significantly higher values in all treatments. Contrary to expectations, biochar and plastic mulch applied separately and together neither increased survival nor reduced the accumulation of toxic TMEs during establishment on soil contaminated with TMEs and after the first growing season. [ABSTRACT FROM AUTHOR]