Abstract
It is important to improve the understanding of the interactions between the trees and pathogens and integrate this knowledge about disease resistance into tree breeding programs. The conifer Norway spruce (Picea abies) is an important species for the forest industry in Europe. Its major pathogen is Heterobasidion parviporum, causing stem and root rot. In this study, we identified 11 Norway spruce QTLs (Quantitative trait loci) that correlate with variation in resistance to H. parviporum in a population of 466 trees by association genetics. Individual QTLs explained between 2.1 and 5.2% of the phenotypic variance. The expression of candidate genes associated with the QTLs was analysed in silico and in response to H. parviporum hypothesizing that (a) candidate genes linked to control of fungal sapwood growth are more commonly expressed in sapwood, and; (b) candidate genes associated with induced defences are respond to H. parviporum inoculation. The Norway spruce laccase PaLAC5 associated with control of lesion length development is likely to be involved in the induced defences. Expression analyses showed that PaLAC5 responds specifically and strongly in close proximity to the H. parviporum inoculation. Thus, PaLAC5 may be associated with the lignosuberized boundary zone formation in bark adjacent to the inoculation site.
Highlights
| INTRODUCTIONJ Baison, K Lundén and L Zhou These authors contributed . The importance of trees and forests for sustaining terrestrial life and biodiversity can probably not be exaggerated (Petit & Hampe, 2006)
The short maintained linkage disequilibrium (LD) and the polygenic nature of the traits controlling resistance suggest that genome-wide association study (GWAS) could be a powerful method to identify further quantitative trait locus (QTL) regions associated with H. parviporum resistance in Norway spruce
We identified candidate genes associated with the QTLs and analysed the expression patterns of the candidate genes in response to H. parviporum hypothesizing that (a) candidate genes linked to the sapwood growth of H. parviporum (SWG) trait would be expressed in sapwood while candidate genes linked to LL are expressed in more peripheral tissues, and; (b) candidate genes that are part of the induced defence are induced in response to H. parviporum inoculation
Summary
J Baison, K Lundén and L Zhou These authors contributed . The importance of trees and forests for sustaining terrestrial life and biodiversity can probably not be exaggerated (Petit & Hampe, 2006). In Norway spruce, resistance to the spruce-infecting congener Heterobasidion parviporum is quantitative in its nature (Arnerup, Swedjemark, Elfstrand, Karlsson, & Stenlid, 2010; Chen et al, 2018; Karlsson & Swedjemark, 2006; Steffenrem, Solheim, & Skrøppa, 2016), and classical interval mapping-based quantitative trait locus (QTL) analysis for resistance to H. parviporum identified 13 QTL linked to host resistance (Lind et al, 2014). The trait control of lesion length extension (LL, with reported heritability values of 0.14–0.33) is measured as the size of the discernible necrosis cells closest to the wound or progressing infection (Arnerup, Lind, Olson, Stenlid, & Elfstrand, 2011; Chen et al, 2018; Steffenrem et al, 2016). The short maintained LD and the polygenic nature of the traits controlling resistance suggest that GWAS could be a powerful method to identify further QTL regions associated with H. parviporum resistance in Norway spruce. We identified candidate genes associated with the QTLs and analysed the expression patterns of the candidate genes in response to H. parviporum hypothesizing that (a) candidate genes linked to the SWG trait would be expressed in sapwood while candidate genes linked to LL are expressed in more peripheral tissues, and; (b) candidate genes that are part of the induced defence are induced in response to H. parviporum inoculation
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