Abstract
Main conclusionTwo terpene compounds and four genes were identified as potential biomarkers for further evaluation for Scots pine susceptibility or tolerance against Heterobasidion annosum.Scots pine (Pinus sylvestris) is one of the main sources of timber in the boreal zone of Eurasia. Commercial pine plantations are vulnerable to root and butt rot disease caused by the fungus Heterobasidion annosum. The pathogen affects host growth rate, causes higher mortality and decreases in timber quality, resulting in considerable economic losses to forest owners. Genetic and biochemical factors contributing to Scots pine tolerance against H. annosum infection are not well understood. We assessed the predictive values of a set of potential genetic and chemical markers in a field experiment. We determined the expression levels of 25 genes and the concentrations of 36 terpenoid compounds in needles of 16 Scots pine trees randomly selected from a natural population prior to artificial infection. Stems of the same trees were artificially inoculated with H. annosum, and the length of necrotic lesions was documented 5 months post inoculation. Higher expression level of four genes included in our analysis and encoding predicted α-pinene synthase (two genes), geranyl diphosphate synthase (GPPS), and metacaspase 5 (MC5), could be associated with trees exhibiting increased levels of necrotic lesion formation in response to fungal inoculation. In contrast, concentrations of two terpenoid compounds, β-caryophyllene and α-humulene, showed significant negative correlations with the lesion size. Further studies with larger sample size will help to elucidate new biomarkers or clarify the potential of the evaluated markers for use in Scots pine disease resistance breeding programs.
Highlights
Scots pine (Pinus sylvestris L.) is a dominant tree species, occupying 64% of Finnish land area, and the largest growing stock, reaching 1157 million m3
Artificial inoculation followed by sampling of lesion areas is commonly done, relying solely on destructive inoculation to screen for resistant genotypes poses a technical and logistical challenge, which may be impractical for large-scale screening of novel biomarkers for durable resistance
One notable challenge is that chemicals induced due to destructive inoculation may be localized within the necrotic lesions
Summary
Scots pine (Pinus sylvestris L.) is a dominant tree species, occupying 64% of Finnish land area, and the largest growing stock, reaching 1157 million m3. It is a species of major economic importance, widely used in timber, pulp, and paper production (Metla 2013). The dynamics of forest ecosystems, including their productivity and economic value, is significantly affected by fungal pathogens. In Northern Hemisphere forests, fungi comprising Heterobasidion annosum s.l. species complex cause root-rot disease of conifer trees (Asiegbu et al 2005). The trees infection by H. annosum, which attacks the sapwood and kills the vascular cambium, causes decreased growth and timber quality, and eventually leads to mortality of trees (Swedjemark and Stenlid 1995; Oliva et al 2011; Gori et al 2013)
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