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Biotechnol Biofuels. 2019 Jun 3;12:135. doi: 10.1186/s13068-019-1479-7. eCollection 2019.

Genetic variation of biomass recalcitrance in a natural Salix viminalis (L.) population.

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1Department of Molecular Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
2Department of Plant Biology, Uppsala BioCenter, Linnean Centre for Plant Biology, Swedish University of Agricultural Sciences, P.O. Box 7080, 750 07 Uppsala, Sweden.
3Department of Plant Physiology and Forest Genetics, Swedish University of Agricultural Sciences, Umeå, Sweden.
4Department of Forest Biomaterials and Technology/Wood Science, Swedish University of Agricultural Sciences, Box 7008, 750 07 Uppsala, Sweden.
5Biosciences Center, National Renewable Energy Laboratory, Golden, CO USA.
6Center for Bioenergy Innovation, National Renewable Energy Laboratory, Golden, CO USA.



Salix spp. are high-productivity crops potentially used for lignocellulosic biofuels such as bioethanol. In general, pretreatment is needed to facilitate the enzymatic depolymerization process. Biomass resistance to degradation, i.e., biomass recalcitrance, is a trait which can be assessed by measuring the sugar released after combined pretreatment and enzymatic hydrolysis. We have examined genetic parameters of enzymatic sugar release and other traits related to biorefinery use in a population of 286 natural Salix viminalis clones. Furthermore, we have evaluated phenotypic and genetic correlations between these traits and performed a genomewide association mapping analysis using a set of 19,411 markers.


Sugar release (glucose and xylose) after pretreatment and enzymatic saccharification proved highly variable with large genetic and phenotypic variations, and chip heritability estimates (h 2) of 0.23-0.29. Lignin syringyl/guaiacyl (S/G) ratio and wood density were the most heritable traits (h 2 = 0.42 and 0.59, respectively). Sugar release traits were positively correlated, phenotypically and genetically, with biomass yield and lignin S/G ratio. Association mapping revealed seven marker-trait associations below a suggestive significance threshold, including one marker associated with glucose release.


We identified lignin S/G ratio and shoot diameter as heritable traits that could be relatively easily evaluated by breeders, making them suitable proxy traits for developing low-recalcitrance varieties. One marker below the suggestive threshold for marker associations was identified for sugar release, meriting further investigation while also highlighting the difficulties in employing genomewide association mapping for complex traits.


Bioenergy crops; Biomass recalcitrance; Enzymatic saccharification; Genetic parameters; Genomewide association study; Lignocellulosic biofuels; Plant breeding; Salix viminalis

Conflict of interest statement

Competing interestsThe authors declare that they have no competing interests.

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