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Languages : en
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Abstract : Evidence for bark, stem and stomatal density adaptation to different climates in the model species Populus is seen in both the natural population as well as in the greenhouse, but the genetic basis of these adaptation remains poorly understood. The present thesis investigates bark texture, bark thickness, diameter and stomatal density variations among Populus population using two quantitative genetics methods to attempt understand the genetic system controlling inheritance of these traits and to associate them with respective genes. The first approach aimed at detecting quantitative trait loci (QTL) associated with all phenotypic traits in an interspecific hybrid pedigree (Populus trichocarpa x P. deltoides and P. deltoides) collected across several years and sites. Identifying QTL for these important traits will pinpoint to polymorphisms linked to functional genes and provide a list of candidate genes and a baseline for future work. QTL specific to bark texture were highly reproducible in shared intervals across sites, years and replicates. Furthermore, significant positive correlations and co-localization between traits QTL suggest pleiotropic regulators or closely linked genes. Since bark texture showed promising results using the low-resolution QTL method, it was then analyzed further using high-resolution population genomic approach, the genome-wide association study (GWAS). Association mapping defined the genomic regions associated with natural variation in bark texture in a clonally replicated provenance trials of P. trichocarpa across three sites, multiple years. The association mapping used with a high-density SNP array allowed us to detect narrow genomic intervals (1-20 kb) with high reproducibility and shared candidate genes for bark texture variation. Several candidate genes were identified related putative function and their location close to QTL maxima were highlighted and are worth further investigation using functional genomics or forward genetics approaches. The results should be exploited for the future conservation and breeding of Populus species.
