The manner in which organisms adapt to climate change informs both a broader understanding of the evolution of biodiversity as well as plans for future conservation and mitigation. We apply common garden and association mapping approaches to quantify genetic variance and identify loci affecting bud flush and bud set, traits that define a tree’s season for height growth, in the boreal forest tree Populus balsamifera L. (balsam poplar). Using data from 478 genotypes grown in each of two common gardens, one near the southern edge and another near the northern edge of P. balsamifera’s range, we found that broad-sense heritability for bud flush and bud set was generally high (H2 > 0.5 in most cases), suggesting that abundant genetic variation exists for phenological response to changes in the length of the growing season. To identify the molecular genetic basis of this variation, we genotyped trees for 346 candidate single nucleotide polymorphisms (SNPs) from 27 candidate genes for the CO/FT pathway in poplar. Mixed model analyses of variance identified SNPs in 10 genes to be associated with variation either bud flush or bud set. Multiple SNPs within FRIGIDA were associated with bud flush, whereas multiple SNPs in LEAFY and GIGANTEA 5 were associated with bud set. Although there was strong population structure in trait variance, except at the most northern populations the geographic distribution of multilocus SNP genotypes was widespread, indicating that geographic regions may harbor sufficient diversity in functional genes to facilitate adaption to future climatic conditions in many populations.

RefSNP_annotation_Dryad_KellerOlsonPoplarRefSNPDataSNP data used to develop Q and A matrices.A_matrixPopPopStructureK matrix for association mappingCandidateSNPSPhenotypes_OlsonEtAl2012