Correlations between selected monoterpene hydrocarbons in the xylem of six Pinus (pinaceae) species

The compositions of 23 monoterpene hydrocarbons of six pine species (Pinus sylvestris, P. yunnanensis ll,ris, P. armandii, P. tropicalis, P. cubensis and P. caribaca) were compared, using multivariate data analysis. Four of the six species were clearly different from the other species in a Principal Components Analysis (PCA) model, based on the relative amounts (selective normalization) of the monoterpenes. The correlation coefficients between constituents were determined separately for each species and the strongest correlations were found between (+)-alpha -pinene and (+)-camphene and between the corresponding (-)-enantiomers, in all species. This pattern, i.e. a good correlation in all species, was neither shown by the correlation of the structurally more similar (+)-alpha/beta -pinenes, nor by the (-)-alpha/beta -pinenes or within the enantiomeric pairs of alpha -pinene and beta -pinene. For these pairs of monoterpenes, good correlations were found in some species. None of the species showed good correlations in all the investigated monoterpene pairs presented here. Correlations between monoterpenes in insect-attacked trees (P. cubensis and P. caribaea, attacked by Dioryctria horneana, and P. yunnanensis, attacked by Tomicus piniperda) were also determined. The results are discussed from chemotaxonomic and biosynthetic points of view.