Impacts of biological, chemical and mechanical treatments on sesquiterpene content in stems of planted Aquilaria crassna trees

Agarwood trade has been growing rapidly due to its active ingredients composed of volatile substances, which are widely used in the cosmetics and pharmaceuticals. However, the formation time of agarwood in nature is quite long and little is known about its formation agents and mechanisms in planted Aquilaria crassna trees. In this study, biological, chemical and mechanical treatments were applied to 5-, 8-, and 11-year-old A. crassna plantations in north central, Vietnam. Agarwood samples were collected at 1 and 2 years after treatment. Oil content (Oc) in dry wood of A. crassna and sesquiterpene content in extracted oil were analyzed using hydrodistillation method and gas chromatography–mass spectrometry. The results indicated that 1 year after treatment, control (no treatment) and mechanical treatment (nails hammered to tree stems) had highest Oc (0.061–0.079 %) but lowest sesquiterpene content (2.1–7.1 %). Chemical treatment (mixture of acid sulfuric and sodium methyl bisulfate) had lowest Oc (0.038–0.039 %) but highest sesquiterpene content (15.8–20.8 %). While, 1 year after treatment biological treatments had Oc of 0.050–0.077 % and sesquiterpene content of 2.4–11.1 %. Two years after treatment, control still had lowest sesquiterpene content (3.2–7.0 %), while highest content (13.9–44.2 %) belonged to biological treatment (a mixture of fungi Phialophora spp. and Fusarium spp.). There was a total of 56 sesquiterpenes found in extracted oil from wood samples in biological treatments, which included eight highly commercially-valuable sesquiterpenes on international trade. Biological treatment with a mixture of fungi P. spp. and F. spp. should be encouraged to apply to 11-year-old A. crassna plantation, which resulted in highest sesquiterpene content (44.2 %).