Phytochemical profile of secondary metabolites in the phloem of mature Pinus pinaster trees attacked by the pine wood nematode

Abstract

The present study highlights, for the first time, the chemical composition of secondary metabolites (lipophilic and hydrophilic compounds) present in the phloem tissues of infected mature Pinus pinaster Ait. trees (on average 74 years old), which may be potentially determinant in the development of the pine wood nematode (PWN) Bursaphelenchus xylophilus. The levels of secondary metabolites in the phloem of infected trees were fairly constant along the height of the trees (an average of 30% dry phloem), but slightly lower compared with total extractives content in the phloem of mature healthy P. pinaster trees (30.0 vs. 39.9%). The hydrophilic fraction represented 91% of the total soluble compounds (27.3% of phloem mass) and it was mainly composed of phenolic compounds and reducing sugars (44.8% and 58.8% of the ethanol-water extracts). The lipophilic fraction (2.7% of phloem mass), was dominated by tricyclic diterpenic compounds (54.2–63.2% of the total lipophilic extracts) and fatty acids. Differences in the relative concentrations of individual compounds were observed compared to healthy pines, suggesting a response to the biotic stress imposed by nematode damage by an increased content of diterpenic resin acids, specifically dehydroabietic and abietic acids, and of total unsaturated fatty acids with a predominance of 9-octadecenoic acid.