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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.

The suitability of miscanthus biomass for anaerobic digestion has already been confirmed by several studies. However, it is rarely used as feedstock in biogas plants, mainly due to uncertainty about the optimal harvest regime with regard to the long‐term methane hectare yield and resilience of the crop to green cutting. The recommended green‐cut date for the only commercially available genotype Miscanthus × giganteus (M×g) ranges from September to November. This timeframe is too broad for agricultural practice and needs to be both narrowed down and further specified for different genotypes. The aim of this study was to identify the most suitable harvest window for an autumn green cut of miscanthus, which delivers both a high dry matter and methane yield while securing the long‐term productivity of the crop. A further objective was to quantify the effect of genotypic differences, such as leaf to stem ratio, on the substrate‐specific biogas and methane yield. For these purposes, a field trial with four genotypes (M×g, GNT1, GNT3, Sin55) was conducted over 2 years (2016/2017) and harvested at 2‐week intervals on three dates between mid‐September to mid‐October. Methane hectare yield ranged from 3,183 m³ CH4 ha−1 a−1 (Sin55) to 5,265 m³ CH4 ha−1 a−1 (M×g), which is mainly influenced by dry matter yield. The substrate‐specific methane yield was higher for the leaf (311.0 ml CH4 (g oDM)‐1) than the stem fraction (285.1 ml CH4 (g oDM)‐1) in all genotypes due to lower lignin content of leaves. Of all genotypes, M×g showed the highest and Sin55 the lowest nutrient use efficiency. We conclude that miscanthus in Germany should be harvested in October to maximize methane yields and nutrient recycling and minimize yield reduction. Additionally, to increase methane hectare yields even further, future miscanthus breeding should focus on a higher leaf proportion. The aim of this study was to identify the most suitable harvest window for an autumn green cut of miscanthus, which delivers both a high dry matter and methane yield while securing the long‐term productivity of the crop. Additionally, we wanted to quantify the effect of genotypic differences (leaf to stem ratio) on the substrate‐specific biogas and methane yield. For these purposes, a field trial with four genotypes was conducted over 2 years and harvested on three dates between mid‐September and mid‐October. We conclude that miscanthus in Germany should be harvested in October to maximize methane yields and nutrient recycling and minimize yield reduction. [ABSTRACT FROM AUTHOR]

Field trials in Europe with Miscanthus over the past 25 years have demonstrated that interspecies hybrids such as M. × giganteus ( M × g) combine both high yield potentials and low inputs in a wide range of soils and climates. Miscanthus hybrids are expected to play a major role in the provision of perennial lignocellulosic biomass across much of Europe as part of a lower carbon economy. However, even with favourable policies in some European countries, uptake has been slow. M × g, as a sterile clone, can only be propagated vegetatively, which leads to high establishment costs and low multiplication rates. Consequently, a decade ago, a strategic decision to develop rapidly multiplied seeded hybrids was taken. To make progress on this goal, we have (1) harnessed the genetic diversity in Miscanthus by crossing and progeny testing thousands of parental combinations to select several candidate seed-based hybrids adapted to European environments, (2) established field scale seed production methods with annual multiplication factors >1500×, (3) developed the agronomy for establishing large stands from seed sown plug plants to reduce establishment times by a year compared to M × g, (4) trialled a range of harvest techniques to improve compositional quality and logistics on a large scale, (5) performed spatial analyses of yield potential and land availability to identify regional opportunities across Europe and doubled the area within the bio-climatic envelope, (6) considered on-farm economic, practical and environmental benefits that can be attractive to growers. The technical barriers to adoption have now been overcome sufficiently such that Miscanthus is ready to use as a low-carbon feedstock in the European bio-economy. [ABSTRACT FROM AUTHOR]

This review addresses the main issues concerning anticipated demands for the use of land for food and for bioenergy. It should be possible to meet increasing demands for food using existing and new technologies although this may not be easily or cheaply accomplished. The alleviation of hunger depends on food accessibility as well as food availability. Modern civilizations also require energy. This article presents the vision for bioenergy in terms of four major gains for society: a reduction in C emissions from the substitution of fossil fuels with appropriate energy crops; a significant contribution to energy security by reductions in fossil fuel dependence, for example, to meet government targets; new options that stimulate rural and urban economic development, and reduced dependence of global agriculture on fossil fuels. This vision is likely to be best fulfilled by the use of dedicated perennial bioenergy crops. We outline a number of factors that need to be taken into account in estimating the land area available for bioenergy. In terms of provisioning services, the value of biofuels is estimated at $54.7-$330 bn per year at a crude oil price of $100 per barrel. In terms of regulatory services, the value of carbon emissions saved is estimated at $56-$218 bn at a carbon price of $40 per tonne. Although global government subsidies for biofuels have been estimated at $20 bn (IEA, 2010b), these are dwarfed by subsidies for fossil fuel consumption ($312 bn; IEA, 2010b) and by total agricultural support for food and commodity crops ($383.7 bn in 2009; OECD, 2010). [ABSTRACT FROM AUTHOR]