# Phytotoxic Substances Involved in Teak Allelopathy and Agroforestry
## 1 Introduction  
Teak (_Tectona grandis_ L.f.), belonging to the family of Lamiaceae, is a large deciduous tree up to 40 m in height. The leaves are ovate (40 cm long, 20 cm wide) and hairy on the lower surface. It has small, fragrant white flowers attached in panicles at the end of its branches. Teak is one of the most valuable timber species because of its beautiful appearance and durable property [1, 2]. Although native to South and Southeast Asia, the significant economic potential of teak wood led the species to be introduced into the agroforestry systems of many countries across tropical Asia, Africa and Central and South America [3, 4, 5, 6, 7].  
Home gardens in tropical and subtropical countries surround residences of local inhabitants, and create small forest-like structures. They are considered to be the traditional agroforestry systems characterized by complexity of the structure and multiple functions. Home gardens consist of various kinds of tree species, with crops, livestock, poultry and fishes--those species have been selected by local inhabitants for their preference, productivity and sociocultural aspects. Home gardens provide various food and goods, including commodities such as animal products, fruits, vegetables, folk medicine, ornamentals, fodder, timber and fuel [8, 9, 10, 11, 12, 13]. Teak is one of the most essential trees in home gardens in South Asia, because it is a very precious wood species and important in folk remedies [8, 14, 15]. Hot water extracts of teak barks are applied for the treatment of bronchitis, biliousness,hyperacidity, diabetes, dysentery, and leprosy. Water extracts of teak leaves are used in pruritus, stomatitis, ulcers and wounds. Hot water extracts of teak roots are applied for anuria treatments. Oil extracts of the flowers are useful for scabies and hair growth. It has also been used as an important plant in Ayurvedic treatments [2; 16].  
Evidence of the pharmacological properties of teak plants has been accumulated over the past decades. Ethanol extracts of teak leaves have shown significant wound healing activity [17]. Ethanol extracts of teak roots have hyperglyemic activity [18]. Ethanol extracts of teak banks show anti-inflammatory and analgesic potentials [19]. Petroleum ether extracts of teak seeds have hair growth activity [20]. Many compounds with pharmacological activities were also isolated from various parts of teak plants [2; 16; 21].  
Some plants have shown excellent weed control abilities as soil additives and/or in intercropping, due to their characteristics of allelopathy [22; 23]. Plants produce hundreds of secondary metabolites. Some of those compounds are released into the surrounding environments through root exudation, volatilization, leaching and decomposition of the plants. Those compounds with allelopathic activity are able to inhibit the growth and germination of neighboring plant species [24; 25; 26]. Therefore, allelopathy of plants is potentially useful for weed management options in several agriculture settings, including agroforestry systems, for the reduction of commercial herbicide dependency [27; 28]. Many phytotoxic substances with allelopathic activity in teak have already been isolated and characterized. However, there has been no review article about the phytotoxic substances involved in teak allelopathy. Thus, this review provides a short overview of allelopathic properties and phytotoxic substances which have allelopathic activities of teak, and discusses the importance of allelopathy for agroforestry systems.