A shift from a fossil-based economy towards a sustainable bio-based economy is urgently needed to fight global climate change Sustainably-grown trees are an excellent feedstock for the production of energy and bio-based products Wood from fast growing trees is currently used for combustion, construction and paper production, and is a promising feedstock for the production of a plethora of materials in future bio-refineries To guarantee a steady production of high-quality wood, continuous breeding is needed towards trees that resist pests and variable weather conditions, while having a high biomass yield and quality New breeding technologies, such as genome-engineering via CRISPR/Cas9, can play an important role to generate such trees However, biosafety regulations do not allow the outdoor growth of trees that harbor CRISPR/Cas9 constructs In addition, the current poplar transformation protocols use transgenes as a selectable marker making them extremely expensive to de-regulate, which hampers their valorization potential Thus, to make genome-engineered poplars attractive for field tests as well as forestry applications, it is of utmost importance to tailor trees without transgenes in their genome Within this project, we pursue complementary strategies to develop a genome-engineering method that allows the direct testing of genome-engineered trees in the field, thereby bridging the gap between controlled greenhouse conditions and industrial applications