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.

Using Populus feedstocks for biofuels, bioenergy, and bioproducts is becoming economically feasible as global fossil fuel prices increase. Maximizing Populus biomass production across regional landscapes largely depends on understanding genotype × environment interactions, given broad genetic variation at strategic (genomic group) and operational (clone) levels. A regional network of Populus field tests was established in the Midwest USA in 1995 to assess relative productivity of 187 clones grown at Westport, Minnesota (45.7°N, 95.2°W); Waseca, Minnesota (only 2000; 44.1°N, 93.5°W); Arlington, Wisconsin (43.3°N, 89.4°W); andAmes, Iowa (42.0°N, 93.6°W). We evaluated biomass potential throughout plantation development and identified clones with yield substantially greater than commercial controls (Eugenei, NM6). For each site, biomass ranges (Mg ha −1 year −1 ) of the best six clones were:

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To increase the understanding of poplar and willow perennial woody crops and facilitate their deployment for the production of biofuels, bioproducts, and bioenergy, there is a need for broadscale yield maps. For national analysis of woody and herbaceous crops production potential, biomass feedstock yield maps should be developed using a common framework. This study developed willow and poplar potential yield maps by combining data from a network of willow and poplar field trials and the modeling power of PRISM-ELM. Yields of the top three willow cultivars across 17 sites ranged from 3.60 to 14.6 Mg ha À1 yr À1 dry weight, while the yields from 17 poplar trials ranged from 7.5 to 15.2 Mg ha À1 yr À1. Relationships between the environmental suitability estimates from the PRISM-ELM model and results from field trials had an R 2 of 0.60 for poplar and 0.81 for willow. The resulting potential yield maps reflected the range of poplar and willow yields that have been reported in the literature. Poplar covered a larger geographic range than willow, which likely reflects the poplar breeding efforts that have occurred for many more decades using genotypes from a broader range of environments than willow. While the field trial data sets used to develop these models represent the most complete information at the time, there is a need to expand and improve the model by monitoring trials over multiple cutting cycles and across a broader range of environmental gradients. Despite some limitations, the results of these models represent a dramatic improvement in projections of potential yield of poplar and willow crops across the United States.

Growth, clone rank, genotype x environment interaction, and effects of early fertilization and irrigation were evaluated for 56 hybrid poplar clones after three years’ growth on two agricultural sites in Indiana, USA. Forty-eight percent of the clones were Populus deltoides x P. nigra (DxN) crosses made with a female parent of Minnesota provenance, with the hybrids or female parent screened in Minnesota for survival, growth rate, and disease tolerance or resistance. Forty-one percent of the clones had at least one parent from provenances that are more southerly and/or have more moderate climates of provenance origin than Minnesota. Eleven percent of the clones were screened in Minnesota but were either not DXN crosses or did not have parents from Minnesota provenances in their parentage. Height growth averaged 1.78 m per year for all clones over all treatments and 2.02 m per year for the fastest- growing six clones (top 10th percentile). Tree bole volume for the fastest-growing 10 % of the clones was 70 % larger than the average of two commercial standard clones. The clonal effect was dominant in comparison to site, treatment, and interaction effects. The fertilizer, irrigation, and fertilizer x irrigation treatments tended to increase growth, but the statistical significance of the treatment effects differed by site, and the treatments explained only a small portion of the variance. Clone rank was the same on both sites, regardless of treatment, except for the fertilizer x irrigation treatment. DxN clones linked to Minnesota parentage out-performed most clones of more southerly or other more moderate climatic origins, in these tests conducted far south of Minnesota. The data provide further evidence of broad adaptability of DxN hybrids with female P. deltoides parents of Minnesota provenance, possibly eliminating the need for narrow breeding zones and reducing the number of screening tests needed at different latitudes, saving time and money. Tests are planned to further analyze and possibly extend this inference.