The increasing demand for the renewable green energy focuses special attention on woody plants grown either in conventional forestry or in energy plantations established on marginal lands. In Hungary, poplar, black locust and willow plantations are primarily used for energy production purposes. Trees in bioenergy farms can be planted in wide spacing and cultivation ensured rapid diameter growth for timber in a 10–15-year rotation time, or as short rotation coppice planted at a high density, and harvested as woody stems in 2–4-year rotation. In these cultivation systems, the biology of tree species differs from those grown in natural forestry; therefore, specific traits are required for economic wood production. Breeding for these traits can only be productive by using the most advanced, science-based methodologies. Intra- and interspecific hybridization can generate significant genetic variability to be utilized by clone selection. Polyploid variants with multiplied chromosome sets can occur in nature and they can be produced by cell division inhibitors. The high wood yield of triploid genotypes may originate from hybrid vigor. Autotetraploid variants with large leaf area and increased CO2 fixation can contribute to the reduction of negative consequences of climate change. Nowadays, increasing the biological capacity of woody energy crops is supported by gene technology. The use of molecular markers in clone selection became an integrated component in tree breeding. Several technologies have been developed to identify and isolate key genes of wood production and these engineered genes are frequently introduced back to tree genomes. The GM trees are tested in confined field trials worldwide. Improved growth parameters and stress tolerance or more efficient wood fermentation were achieved by the introduction of genes. Currently, genome editing tools open a new area in precision plant breeding since directed mutagenesis can lead to designed tree traits even without the introduction of a new gene. In this study, we provide an overview of some selected features of modern tree breeding combining the traditional and molecular approaches.

Keywords: wood species, green energy, cross-breeding, polyploidy, genetic incorporation, genome editing