Development of mutation-based breeding technology in forest tree species

Agricultural breeding based on phenotypic selection of desired variants in self-fertilized populations has been highly successful. This approach has not been applied successfully to forest trees due to the constraints from long generation times and difficulties with controlled large-scale self-fertilization. Novel technologies allow identification of mutants based on DNA sequence deviations in heterozygous mutants, potentially circumventing the need for identification based on phenotype. To test this approach, we generated >6000 poplar trees from mutagenized calli and screened for genetic variants in targeted genes using TILLING technology. While we found genetic variants, DNA sequencing suggested that they were due to natural rather than induced genetic variation. As an alternative approach, we tested mutagenesis of willow pollen and generated a mutant population. We thereafter used novel DNA sequencing technology to screen for genetic variants in targeted loci. This approach identified potential mutants that cannot be explained by background natural variation.