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Doctoral thesis2022Open access

Genetics of disease resistance in Norway spruce (Picea abies) : a look in the past with an eye to the future

Capador-Barreto, Hernán Dario


Trees have evolved strategies to fight enemies and survive during their million-year history. These strategies have been shaped by natural selection and are reflected in their genomes today. Tree planting is a priority for governments, but there is a risk that trees selected by humans will lack alleles important for disease resistance. Norway spruce (Picea abies) is a characteristic species in the Swedish landscape and one of the most important trees for the forest industry. Therefore, the overall aim of this thesis was to study the genetic variation of resistance traits in Norway spruce to Heterobasidion parviporum and Heterobasidion annosum s.s., two fungal pathogens causing root and stem rot in conifers. In the first two papers, the genomic basis of resistance traits was studied with genome-wide association studies (GWAS). Associations between single nucleotide polymorphisms (SNPs) and resistance traits led to the discovery of several variants, with relatively small effects, associated with resistance to each pathogen. Correlation of resistance traits to these two species was dependent on the environment but using GWAS pleiotropic SNPs associated with resistance to both pathogens were found. Synergistic pleiotropic SNPs are genes that could provide multiple disease resistance in trees. In the third paper, signatures of selection in PaLAR3 were studied. This gene is associated with defence against pathogenic fungi in Norway spruce. Genomic analyses demonstrated that variation in PaLAR3 has been likely maintained by balancing selection in Norway spruce. Moreover, it seems that this process started before Norway spruce isolated reproductively from white spruce (Picea glauca). In the fourth paper, resistance in the bark was studied in ten Norway spruce genotypes varying in susceptibility, inoculated with five Heterobasidion isolates varying in virulence. Both host and pathogen influenced the length of lesions in the bark. Using differential gene expression and co-expression networks, it was shown that Norway spruce genotypes with relatively high resistance had a robust response, which included the expression of pathogen recognition genes. In contrast, in a more susceptible host, the response was dependent on the virulence of the H. annosum s.s. isolate. Overall, the thesis advances the knowledge on disease resistance in Norway spruce. This knowledge will support the Swedish Norway spruce breeding program decision making in selecting healthier trees in the future.


genome wide association study (GWAS); pleiotropy; balancing selection; gene evolution; quantitative disease resistance; RNA-seq

Published in

Acta Universitatis Agriculturae Sueciae
2022, number: 2022:3ISBN: 978-91-7760-881-3, eISBN: 978-91-7760-882-0
Publisher: Swedish University of Agricultural Sciences