Genetics, genomics and crop modelling: integrative approaches to the improvement of biomass willows

Willows (Salix spp.) grown as short rotation coppice (SRC) are among the leading commercially grown biomass crops in temperate regions, however, compared with major arable crops they are relatively undomesticated. Initial advances in improving the crop were made by selecting stem characteristics (height, diameter, straightness) and coppicing response (shoot number, shoot vigour), as well as resistance to pests, diseases and environmental stress. Selections were achieved purely on the basis of phenotype, with little understanding of the genetics for many of these important traits, or how they interact with each other and the environment. To enhance yields further, and to adapt the crop to future climates and more marginal environments where biomass crops will be encouraged, a more holistic understanding is needed of the key traits to target and expected gene-environment interactions. In this chapter we begin by reviewing what is known about growth in willow in relation to the parameterisation of process-based models and the advances made in willow genetics and genomics. We finish by considering an integrative approach which feeds genotypic information into phenotypic models of source-sink interaction to identify target traits for crop improvement.