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

Abstract

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 (O c ) 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 O c (0.061-0.079 %) but lowest sesquiterpene content (2.1-7.1 %). Chemical treatment (mixture of acid sulfuric and sodium methyl bisulfate) had lowest O c (0.038-0.039 %) but highest sesquiterpene content (15.8-20.8 %). While, 1 year after treatment biological treatments had O c 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 commerciallyvaluable 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 %).

Agarwood Induction: Current Developments and Future Perspectives

“…Instead of relying on external stimuli to trigger plant responses, either by mechanical wounding or biological inoculum, some induction approaches have been developed to introduce signaling molecules directly and specifically into Aquilaria trees to initiate agarwood resin biosynthesis pathways (Liu Y. et al, 2013; Wu et al, 2017). Chemical inducers normally comprise of phytohormones, salts, minerals and biological-derived substances (Zhang et al, 2012; Liu Y. et al, 2013; Van Thanh et al, 2015). Besides, suitable delivery method is often developed together with the chemical formulations to ease the large-scale induction process, such as vessel equipped with transfusion needle (Yang et al, 2014c).…”

Understanding Agarwood Formation and Its Challenges

“…The identities of chemicals in patents are generally not made public, or their strengths and formulations are kept discrete. They could be in the form of plant defense elicitors such as hydrogen peroxide (H 2 O 2 ), methyl jasmonate (MJ), or salicylic acid (SA) (Okudera and Ito 2009 ;Wijitphan 2009 ;Wei et al 2010 ) or chemicals such as sodium chloride, sulfuric acid, formic acid, and sodium methyl bisulfi te (Thanh et al 2015 ). Chemical-based inducer acts by causing severe injury to Aquilaria cell structure, and as a result callusing cannot be performed to cover up the wound.…”

“…Another important factor is the treatment applied onto the tree to induce agarwood. In a fi eld trial conducted in planted A. crassna , Thanh et al ( 2015 ) showed that agarwood oil samples from different treatments including biological (fungal mixture), chemical (sulfuric acid and sodium methyl bisulfi te mixture), and mechanical (hammered nails) differ in quantity and quality. A year after, chemical treatment yielded agarwood oil with the highest sesquiterpene content compared to the other treatments and non-treated.…”

Fusarium solani induces the formation of agarwood in Gyrinops versteegii (Gilg.) Domke branches

“…The physical or mechanical manipulations have usually been performed by wounding, boring, or nailing, but agarwood formation in response to these treatments still takes a long time and was of poor quality (Liu et al 2013). Chemical agents, such as jasmonic acid (Xu et al 2016), methyl jasmonate, salicylic acid (Okudera and Ito 2009), sulphuric acid (Thanh et al 2015), and hydrogen peroxide (Lv et al 2019) have also been tried. These treatments did induce agarwood formation in a relatively shorter time than in the wild but there are environmental concerns about their use (Turjaman et al 2016).…”