Abstract
The short rotation biomass crop willow (Salix genera) has been of interest for bioenergy but recently also for biofuel production. For a faster development of new varieties molecular markers could be used as selection tool in an early stage of the breeding cycle. To identify markers associated with growth traits, genome-wide association mapping was conducted using a population of 291 Salix viminalis accessions collected across Europe and Russia and a large set of genotyping-by-sequencing markers. The accessions were vegetatively propagated and planted in replicated field experiments, one in Southern Sweden and one in Central Sweden. Phenology data, including bud burst and leaf senescence, as well as different growth traits were collected and measured repeatedly between 2010 and 2017 at both field environments. A value of the plasticity for each accession was calculated for all traits that were measured the same year in both environments as the normalized accession value in one environment subtracted by the corresponding value in the other environment. Broad-sense accession heritabilities and narrow-sense chip heritabilities ranged from 0.68 to 0.95 and 0.45 to 0.99, respectively for phenology traits and from 0.56 to 0.85 and 0.24 to 0.97 for growth traits indicating a considerable genetic component for most traits. Population structure and kinship between accessions were taken into account in the association analyses. In total, 39 marker-trait associations were found where four were specifically connected to plasticity and interestingly one particular marker was associated to several different plasticity growth traits. Otherwise association consistency was poor, possibly due to accession by environment interactions which were demonstrated by the low structure adjusted accession correlations across environments (ranging from 0.40 to 0.58). However, one marker association with biomass fresh weight was repeatedly observed in the same environment over two harvest years. For some traits where several associations were found, the markers jointly explained over 20% of the accession variation. The result from this study using a population of unrelated accessions has given useful information about marker-trait associations especially highlighting marker-plasticity associations and genotype-by-environment interactions as important factors to take account of in future strategies of Salix breeding.
Highlights
Fast growing trees for bioenergy has been of interest since the 1980s and lately the increasing demand of non-fossil fuels has further put fast growing woody biomass production into focus
We investigated associations between a genome wide set of markers and growth and phenology related traits, measured repeatedly during several years and in two different environments
Genome wide association studies with biomass traits has never been conducted in Salix viminalis but recently within the same genera in S. purpurea (Carlson et al, 2019)
Summary
Fast growing trees for bioenergy has been of interest since the 1980s and lately the increasing demand of non-fossil fuels has further put fast growing woody biomass production into focus. Salix viminalis has a history of cultivation to provide raw material for basketry and for stabilization of river banks across Europe and has been domesticated to some degree due to trading of clonal material between countries resulting in successive expansion of the species geographic distribution (Lascoux et al, 1996; Kuzovkina et al, 2008; Berlin et al, 2014). Despite this the Salix species of interest for SRC are still at a low level of domestication implying substantial genetic variation within species and a high degree of individual heterozygosity (Berlin et al, 2011, 2014). Recurrent selection programs have developed cultivars with increased biomass production compared to old varieties originating from wild collections (Åhman and Larsson, 1994; Larsson, 1998; Kuzovkina et al, 2008; Karp et al, 2011)
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