Abstract
AbstractConstitutive and inducible terpene production is involved in conifer resistance against insects and fungal infestations. To gain knowledge about local defence responses of Norway spruce bark against pathogens and to find potential chemical markers for resistance breeding, we inoculated the stem of 8‐year‐old Norway spruce (Picea abies) clonal trees with both Endoconidiophora polonica (Ep, a common fungal pathogen associated with the spruce bark beetle Ips typographus) and Heterobasidion parviporum (Hp, a severe pathogen causing root and stem rot disease). Three weeks after inoculation, the fungal‐inoculated and intact bark from each tree was sampled. The terpenes in tree bark were extracted with hexane and characterized by gas chromatography–mass spectrometry (GC‐MS). The two fungi induced varied terpene responses in the four spruce clones used. Three of the clones showed a 2.3‐fold to 5.7‐fold stronger terpene response to Hp relative to Ep inoculation, while one clone responded similarly to inoculation with the two fungal pathogens. The amount of the diterpenes thunbergol and geranyllinalool varied between the clones. The level of thunbergol was higher in both intact and fungal‐inoculated bark from the less susceptible clones compared with the more susceptible clones. Geranyllinalool was present in higher amounts in the susceptible clones and is thus a possible marker for susceptibility. Our observations show that Norway spruce employs a similar chemical mechanism against the two fungal pathogens. Based on the present and earlier published data, we suggest that certain Norway spruce genotypes have a strong defence reaction against these two pathogens. The diterpenes thunbergol and geranyllinalool might be useful markers of susceptibility in tree‐breeding programmes and should be the focus of further detailed investigations.
Highlights
Conifers are long-lived trees that face many threats during their lifetime
The ability of conifers to react to various stressors by production of high amounts of defence chemicals likely contributes to their long survival
Since less susceptible trees usually show stronger terpene responses upon infection (Schiebe et al, 2012; Zeneli et al, 2006; Zhao, Krokene, et al, 2011b), terpene increases following experimental fungal inoculation are often used as a measure to evaluate tree susceptibility towards bark beetles and pathogens (Fäldt et al, 2006; Krokene, 2015)
Summary
Norway spruce (Picea abies), ecologically and economically the most important conifer species in Europe, is often threatened by the spruce bark beetle (Ips typographus) and its associated fungi including Endoconidiophora polonica (Ep), which causes huge economic losses (Wermelinger, 2004). The Heterobasidion species complex represents some of the most serious pathogens of Norway spruce in Scandinavia by causing root and stem rot and rendering the timber defective for sawing and pulping (Thor, 2005). These decay fungi are commonly spread by airborne spores that upon landing on freshly cut stump surfaces give rise to mycelia that grow further to the neighbouring living trees through root contacts. Certain terpenes inhibit the growth of decay fungi (Kusumoto et al, 2014)
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