Abstract
When conifers such as Chinese white pine (Pinus armandi Fr.) are attacked by insects or pathogens, they respond by increasing their content of monoterpenes and sesquiterpenes. In this study, we determined the effects of the blue-stain fungus Leptographium qinlingensis Tang and Chen on monoterpenes and sesquiterpenes in the phloem and xylem of the stem of P. armandi saplings. We found that the total monoterpene concentrations in the phloem and xylem of the stem and the total sesquiterpene concentrations in the xylem of the stem were significantly higher in L. qinlingensis-inoculated saplings than in control (mechanically wounded) saplings or untreated saplings. Additionally, the proportions of β-pinene in the xylem of the stem and limonene + β-phellandrene in the phloem and xylem of the stem were significantly higher in L. qinlingensis-inoculated saplings than in both control and untreated saplings. The proportions of individual sesquiterpenes in the phloem and xylem of the stem were significantly greater in L. qinlingensis-inoculated saplings than in untreated saplings. Based on the results of this study, we suggest that increases in total monoterpene and sesquiterpene concentrations, as well as increases in the concentrations of β-pinene and limonene + β-phellandrene, may play an important defensive role against blue-stain fungus L. qinlingensis inoculation.
Highlights
When conifers are attacked by pests and pathogens, they develop physical and chemical defenses to protect their tissues [1,2]
Comparisons of total monoterpene concentrations among time points after treatment in individual treatments showed that the total monoterpene concentrations in the xylem differed significantly among time points after treatment in L. qinlingensis-inoculated saplings (F = 9.98, df = 2, p = 0.018), whereas the corresponding total concentrations did not differ significantly among time points after treatment in control and untreated saplings
L. qinlingensis-inoculated saplings and at 8 days (t = −1.291, p = 0.035) for control saplings, with a greater increase in the xylem than in the phloem (Figure 5c). This is the first study in which changes in monoterpene and sesquiterpene chemical defence compounds have been compared in the phloem and xylem in P. armandi saplings after mechanical wounding and inoculation with the blue-stain fungus L. qinlingensis
Summary
When conifers are attacked by pests and pathogens, they develop physical and chemical defenses to protect their tissues [1,2]. The major chemical defenses of conifers against insects and pathogens involve terpenoid-based oleoresins and phenolics [3]. The quantitative and qualitative terpenoid composition of the oleoresin and volatile constituents can significantly change the response of the conifers to insect and fungal attack [6,7,8,9]. The Chinese white pine (Pinus armandi Fr.) is a coniferous species that is native to China. It is found in the Qinling and Bashan Mountains [14]. Since 1954, the blue-stain fungus Leptographium qinlingensis Tang and
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