Improving Poplar for Biofuel Applications: Elucidating the Genetic Basis of Important Traits in Populus nigra through an Association Genetics Approach in a Natural, Wide Mapping Population

This project is centred on a natural, wide population of Populus nigra (black poplar) genotypes, drawn from across Western Europe and under SRC cultivation in field trials in the south of England and the north of Italy. Ongoing phenotyping at these sites is seeing the population assessed for key bioenergy traits including biomass yield, leaf development, stomatal patterning, saccharification potential, water-use efficiency and drought tolerance. The population has been previously genotyped using an Illumina Infinium II 12K BeadChip array with single nucleotide polymorphisms (SNPs) drawn from QTL and candidate gene regions for saccharification, biomass and water-use efficiency in this species. This provided around 8000 informative SNP markers suitable for an association genetics approach to identify candidate genes for traits of interest. Around 20 such genes were identified as well as valuable information on linkage disequilibrium (LD) decay and population substructure. LD was found to decay to r²<0.1 within around 30kb. Population structure shows a strong geographical influence with the strongest genetic differentiation identified between the Northern Italian and Spanish genotypes; a result consistent with the observed phenotypic variation. We are now undertaking genotyping by sequencing (GBS) in this population with a view to greatly increasing our number of available markers to permit a far more extensive GWAS later this year. The identification of trait-marker associations also raises the prospects for the future application of advanced breeding techniques, such as marker assisted and genomic selection, in poplar for increased yield, an improved feedstock and more efficient bioethanol production.