Agarwood forms in the heartwood of Aquilaria trees after they become infected with the mould Phaeoacremonium parasitica. The tree secretes a resin to combat the fungal infestation. Before infection the heartwood mostly lacks scent and is relatively light and pale. As the infection advances, the heartwood becomes very dense, dark and saturated with resin. The resin is not produced in normal wood tissues; it forms only when the plant is injured, for example by wind, lightning, gnawing by ants or insects, or by microbial infection. These natural processes are slow and occur by chance, so the agarwood develops very slowly over decades. Growers also induce it artificially by burning, holing or cutting the trees, or by inoculating them with fungi such as Fusarium. In planted forestry, inoculating the trees with the fungus is a common method.
Aquilaria malaccensis is found in Bangladesh, Bhutan, India, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Cambodia. The name Aquilaria agallocha is a synonym of Aquilaria malaccensis. Since 1995 the Convention on International Trade in Endangered Species of Wild Fauna and Flora has listed Aquilaria malaccensis, the primary source, in its Appendix II. Aquilaria malaccensis is considered critically endangered on the IUCN Red List. India is promoting the sustainable cultivation of Aquilaria malaccensis to support the economic growth of the northeastern states. Agarwood plantations have been established in countries such as India, Bangladesh and Bhutan.
The composition of agarwood oil is exceedingly complex, with more than 150 chemical compounds identified. At least 70 of these are terpenoids, in the form of sesquiterpenes and chromones; no monoterpenes have been detected at all. The exact balance of these materials varies with the age and species of the tree and with the details of the oil extraction process. Sesquiterpenes found in the genus Aquilaria include compounds with guaiane, eudesmane, eremophilane, agarofuran, agarospirane or prezizane skeletons. Agarospirol has been isolated from the agarwood of infected A. agallocha. Jinkoh eremol and kusunol are eremophilane sesquiterpenes identified in A. agallocha agarwood. All chromones isolated from Aquilaria species are derivatives of 2-(2-phenylethyl)chromone. The varying aromatic qualities of agarwood are influenced by the species, geographic location, the part of the tree it comes from, the time since infection, and the methods of harvesting and processing.
Agarwood has thousands of years of known use and is valued across Hindu, Buddhist, Muslim and Chinese cultures. In Saudi Arabia and other Arabic countries, the wood of Aquilaria trees is used as incense at important religious occasions. Wood from closely related species is used during Buddhist ceremonies in Asian countries such as Japan and India. The bark of Aquilaria malaccensis is used in the traditional Assamese manuscript, the sanchipat.
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Related: Agarwood Oil · Agarwood Oud · Australian Oud · Cambodian Oud · Chinese Oud · Indonesian Oud · Laotian Oud · Malaysian Oud