The al., 2017). It was discovered that agarwood

The
plant genus Aquilaria is an evergreen
tropical woody tree that is well known for its fragrant resin called agarwood.
Nineteen accepted species have been reported up to date growing from India
through Burma, Laos, Vietnam and Cambodia to Malaysia, Sumatra, Borneo, the
Philippines and Papua–New Guinea, all of them producing agarwood (Naef, 2011). Aquilaria has been known by many names;
in Malaysia and Indonesia, it is called as “gaharu”, “chenhsiang” or
“chenxiang” in China; “jin-koh” in Japan; “agar” in India; “chim-hyuang” in
Korea; “kristsananoi” in Thailand; “tram huong” in Vietnam; “bolsd’agle”, or
“calambour” in French and “oud” in the Middle East (Lee et al., 2016). The resin is
produced by the Aquilaria and Gryinops trees as a self-defence mechanism where
it marinate in the heartwood as a consequence of natural immune response
towards fungal attack (Ibrahim et al., 2011). The immune
system of the tree is activated after wounding of the stem (e.g. by elephants)
and infection by various fungi or insects. An oleoresin rich in volatile
organic compounds is formed and activates the healing process by retarding the
fungal growth (Naef, 2011).

Due
to high demand of agarwood on the market, natural Aquilaria that stands in the wild are heavily exploited. Their
natural population sizes are greatly reduced as a result of illegal and
indiscriminate harvesting of Aquilaria
trees. Mother trees are felled and the regeneration cycle is disturbed,
threatened the survival of the trees in the wild. Consequently, this results in
the drastic decline of Aquilaria
trees in natural forests and earned it the endangered status. The genus is
currently listed in Appendix II of the Convention on International Trade in
Endangered Species of Wild Fauna and Flora (CITES) (CITES, 2011). Recent efforts
has been developed in producing sustainable agarwood and leads to cultivation
of Aquilaria tree in
agarwood-producing countries including China, Malaysia, Thailand, Cambodia,
Vietnam, Laos, Australia, and Sri Lanka (Adam et al., 2017).

It
was discovered that agarwood was first used as one of traditional Chinese
medicines from the 5th century where it was used in more than 1500
kinds of preparations of Chinese medical materials. It was also known that
agarwood has been used as incense in Buddhist, Hindu, and Islamic ceremonies
for centuries. It was believed that agarwood incense is used to remove curse in
traditional Ayurveda medicine. Meanwhile, traditional Arab medicine has been
using agarwood essential oil for aromatherapy. Presently, more than 18
countries throughout Southeast Asia and Middle East have participated in
agarwood trade (Liu et al., 2017). In practice,
only the heartwood of A. malaccensis (synonymous A. agallocha), A. crassna, A.
sinensis and, recently, A. filaria are commercially exploited (Naef, 2011). In recent years,
the applications of Aquilaria leaves
has broadened to food products where it is diversified and sold in the forms of
tea in sachets, or mixed with coffee, biscuits, and ice-creams. Agarwood tea,
also known as ‘teh gaharu’ or ‘teh karas’ in the Malay language, is commonly
accepted as a new herbal drink which is usually produced from the young shoots
of Aquilaria trees. It is believed to
have health benefits to humans (Adam et al., 2017).