Association Genetics of Wood Chemical Properties in Populus Species

The need for alternative sources of energy has led to recent efforts for developing renewable sources for biofuels. Species belonging to Populus genus (poplars) have several advantages impacting the efficiency of cellulosic ethanol production. Traditional genetic improvement of poplars for bioenergy production can be enhanced by genomics-based breeding technologies. In this context, the development of association studies utilizing SNP-markers have greatly benefited during last few years from high throughput technologies for sequencing and genotyping. This work describes the main results of a research line focused on the analysis of genetic polymorphisms underlying the phenotypic variation of wood chemical properties in Populus species, including P. trichocarpa, P. nigra, P. alba, and P. fremontii. Candidate genes utilized for analysis encode a series of enzymes related to cellulose and lignin biosynthesis pathways. Sequence analyses have been performed to estimate nucleotide diversity, divergence, and neutrality across all species. Additionally, for P. trichocarpa and P. nigra wood, pyrolysis molecular beam mass spectrometry was used to determine contents of 5- and 6-carbon sugars, lignin, and syringyl-guaiacyl ratio.  Statistical analyses were carried out to estimate linkage disequilibrium (LD), and single SNP-marker and haplotype-based associations. Significant associations between traits and single markers or haplotypes, from candidate genes, have been identified.  The rapid decay of LD within genes in the studied populations, and the genetic associations identified, suggest a close relationship between the associated SNPs and the causative polymorphisms controlling the genetic variation of lignocellulosic traits in poplars.