Pinus pinaster subsp. chemotypes, Aiton, Aiton
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publication ID |
https://doi.org/ 10.1016/j.phytochem.2019.112159 |
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persistent identifier |
https://treatment.plazi.org/id/03B7520F-F667-FFEE-FC99-EFE3FA9991A2 |
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treatment provided by |
Felipe |
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scientific name |
Pinus pinaster subsp. chemotypes |
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2.1. Pinus species assessed and P. pinaster chemotypes
The 38 P. pinaster trees assessed belonged to four families of half-sib progenies of selected trees that showed variable survival to pine wilt disease, Table 1 View Table 1 . These families resulted from a mass selection program based on the absence of PWD symptoms, and on morphological criteria such as tree dominance in a stand, age, and diameter> 20–25 cm at breast height ( Carrasquinho et al., 2018). Whereas no previous work has addressed possible relationships between survival and the chemical composition of tree volatiles, the studies of Rodrigues et al. (2017) have stressed the importance of knowing each P. pinaster tree chemotype because the influence of different phytochemical profiles on either choice of host tree by the insect vector, or resistance to PWN, is still unknown.
To assess whether P. pinaster chemical variability might result in different responses to M. galloprovincialis feeding, we first determined the chemotype of each P. pinaster tree in our study. Chemotypes are chemically distinct groups within phenotypically similar members of a species. A chemotype is defined by the different types and proportions of the main chemical constituents of the essential oils (EOs) ( Figueiredo, 2017). Thus, the C1 chemotype was characterized by the presence and proportions of β-pinene, α-pinene, and δ-3-carene, whereas the C2 chemotype was characterized by β-pinene and α-pinene and the C3 chemotype was characterized from the ratios of α-pinene and β-pinene, Table 1 View Table 1 . Representative GC-MS profiles of each chemotype are provided in Supplementary File (SF) Fig. 1 View Fig .
* Predicted survival mean (%) according to Carrasquinho et al. (2018). ** Chemotypes determined previous to SPME experiments and classified according to Rodrigues et al. (2017). Each individual chemotype was evaluated based on the essential oil of each tree, as detailed in the experimental section.
<0.0001***.
Of the 38 P. pinaster trees assessed, 11 had C 1 type essential oils, 25 belonged to C2 , and 2 belonged to C3 , Table 1 View Table 1 . Given the low number of C3 EO trees, for simplicity, they were considered together with C2 (both with trace amounts of δ-3-carene) and only the C1 and C2 groups were evaluated further .
In contrast to P. pinaster, Rodrigues et al. (2017) had shown that the essential oils of P. pinea trees have only a single chemotype, and the EO is dominated by limonene. In addition, in natural stands, P. pinea is not affected by PWD.
2.2. Comparison of volatiles from the two Pinus species
Volatiles were sampled from each Pinus ssp. and chemotype by SPME, both before and during feeding by M. galloprovincialis . For each Pinus species, the chemical composition is shown in Tables 2 View Table 2 and 3 View Table 3 , in order of their elution on a DB-1 column. The changes in the amounts of volatiles released during feeding by Monochamus are shown relative to the original amounts (fold increase) emitted from the same tree before being exposed to insect feeding (control).
2.2.1. Pinus pinaster volatiles, before and during feeding by Monochamus galloprovincialis
In total, 17 components were detected by SPME analysis of P. pinaster volatiles before M. galloprovincialis feeding, Table 2 View Table 2 . Comparable chromatographic profiles were obtained for each P. pinaster tree, in qualitative terms, although with some variations in the relative amounts of the different components, Table 2 View Table 2 . The monoterpene hydrocarbons β-pinene and α-pinene were always the dominant emitted volatiles. When detected, β-caryophyllene, germacrene D, and δ-3-carene were also among the main emitted volatiles.
During M. galloprovincialis feeding, in general the release rates of all chemical compounds increased, with β-pinene and α-pinene showing the highest increases (148- and 138-fold increase, respectively) (F (16,629) = 4.07; p <0.0001), followed by two sesquiterpene hydrocarbons, β-caryophyllene (83-fold increase) and germacrene D (54-fold increase) (F (14,555) = 4.63; p <0.0001), Fig. 1 View Fig .
All the emitted volatiles, before and during M. galloprovincialis feeding, had been detected previously in different types of P. pinaster extracts or essential oils ( Rodrigues et al., 2017 and refs. cited therein). The studies of Rodrigues et al. (2017) on the essential oil composition from healthy and mechanically damaged P. pinaster did not show major qualitative and quantitative differences.
Previous work had examined P. pinaster volatiles collected with adsorbents ( Blanch et al., 2012), and by SPME ( Paiva et al., 2011). However, in the latter study, instead of analysing plant volatiles in situ, SPME analyses were conducted on hexane extracts of P. pinaster needles, so direct comparisons with the data obtained in the studies reported here are not possible.
When analysing the two chemotypes separately, β-caryophyllene and germacrene D showed the highest fold increase (72- and 41-fold increase, respectively) in the C1 group during M. galloprovincialis feeding, and the results were marginally significant (F (16,170) = 1.58; p = 0.078), whereas in the C2 group, β-pinene and α-pinene dominated (201- and 185-fold increase, respectively), and the differences were statistically significant (F (16,442) = 4.04; p <0,0001), Fig. 2 View Fig .
Thus, two chemotypes responded differently to feeding by the beetles, with the responses of C 1 type trees showing a trend of being dominated by increases in sesquiterpene hydrocarbons, whereas the monoterpene hydrocarbons showed the highest fold increase in C 2 type trees, particularly β-pinene and α-pinene.
However, there was no correlation between the increases in volatiles and the families of origin, Table 1 View Table 1 , which may be partially explained by the fact that the families resulted from grouping by growth parameters and the absence of PWD symptoms, rather than grouping by different chemotypes.
Previous studies have shown that a correlation may exist between the type and balance of the dominant volatiles of a species and its susceptibility to infestation. Annila and Hiltunen (1977) showed a negative correlation between α-pinene content and the percentage of Pissodes validirostris (Sahlberg) infested cones in P. sylvestris (Scots pine), whereas 3-carene, myrcene, β-phellandrene, and p -cymene were more abundant in the volatiles from severely attacked trees.
Based on the data obtained in the present study, future work should evaluate the relationship between the survival rate of P. pinaster families and the dominant chemotype of individual trees, by assessing the EO composition of each tree that survives attack by PWN. For example, if C2 trees with a lower δ-3-carene content are less attractive to the insect vector, this will decrease the likelihood of PWN inoculation, and consequently positively affect the P. pinaster survival rate.
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University of Copenhagen |
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