# Phytotoxic Substances Involved in Teak Allelopathy and Agroforestry
## 4 Phytotoxic Substances with Allelopathic Activity in Teak  
Phytotoxic substances with allelopathic activity identified in teak are discussed in this section. All phytotoxic substances listed in Table 2 and Figure 1 were isolated from fresh teak leaves with water. Naphthotestone (3) inhibited the germination and seedling growth of wheat (_Triticum aestivum_ L.), onion (_Aliium cepa_ L.), tomato (_Lyopersicon esculentum_ L.), and lettuce (_Lactuca sativa_ L.) [53]. Rhinocerotinoic acid (8) suppressed the germination and seedling growth of wheat and lettuce [54]. 2-Oxokovalenic acid (9) and 19-hydroxyferuginol (11) inhibited the germination and seedling growth of wheat, onion, lettuce; 3\(\beta\)-hydroxy-7,8-dihydro-\(\beta\)-ionol (15) inhibited the seedling growth of wheat, onion and tomato; and 3\(\beta\)-hydroxy-7,8-dihydro-\(\beta\)-ionone (16) inhibited the seedling growth of wheat, onion, tomato and lettuce [55]. Other compounds listed in Table 2 inhibited the seedling growth of wheat [54; 55; 56]. Although those compounds were isolated and identified from teak leaves for potential use as a source of natural herbicide model and/or bioactive compounds, the allelopathic effects of those compounds were determined only by crop plants. It may be necessary to determine the activity of those compounds on weed species. \begin{table}
\begin{tabular}{c c c c} \hline
**Source** & **Inhibition** & **Target Plant Species** & **Reference** \\ \hline Leachate from leaves & Germination, plant growth & _Vigna unguiculata_, _Momordia charantia_, _Solanum melongena_ & [37] \\ Leaf mulch & Rhizome growth & _Cicer arietinum_ & [38] \\ Leaf powder & Weed emergence & _Cyrenta rotundus_, _Cyrerus difforms_, _Amarantihus viridis_, _Chenopodium album_, _Mellibatus alba_ & [39] \\ Extracts & & _Vigna mungo_, _Vigna radiata_ & [40; 41] \\ Soil under teak trees & Germination, plant growth, protein content & _Echinochla colona_, _Cyrenta difforms_ & [42] \\ Fallen leaf & & _Cyrndon dactylon_, _Echinochla colona_, _Cyrenta rotundus_, _Cyrenta difforms_, _Amarantihus viridis_, _Chenopodium album_, _Mellibatus alba_ & [43] \\ Fresh leaf & Germination, plant growth & _Vigna mungo_ & [44] \\ Germination, plant growth & _Plumbago zyelanica_ & [45] \\ Rice, maize, _Vigna radiate_, _Vigna umbellate_, _Arachis hypogeae_ & [46] \\ Germination & _Luffa cylindrical_, _Ablosmchus esculenttus_, _Brassica juncea_ & [47] \\ Plant growth, contents of chlorophyll and carotenoid & _Chilli_, _Vigna radiata_ & [48] \\ Plant growth, contents of chlorophyll and carotenoid & _Pemisetum glaucum_, _Eleusine coracana_ & [49] \\ Plant growth & _Amaranthus spinosus_ & [50] \\ Root & Germination, seedling growth & _Hibiscus esculenttus_ & [51] \\ Leaf, root, bark & Plant growth & Maize & [52] \\ \hline \end{tabular}
\end{table} 
Table 1: Allelopathic activity of the leachate, leaves and extracts of teak and target plant species. Several phenolics were also identified in teak barks and leaves [39; 50; 57]. Phenolic compounds have been found in a wide range of plants and soils, and often mentioned as putative allebotathic substances [58; 59]. The importance and contribution of those phenolics found in teak are not clear because no information regarding the phytotoxic activity of those compounds for teak allebotathy is available in the literature. However, gallic and ellagic acids were identified in teak leaf extracts [60], and the allebotathic activity of those compounds isolated from other plant sources were reported [61; 62]. Therefore, some phenolics in teak plants may contribute to the allebotathy of teak. Phenolic compounds inhibit some enzyme activities and physiological processes, such as plant hormone functions, water balance and mineral uptake, as well as stomatal functions, respiration, and photosynthesis [58; 63]. A number of secondary metabolites in many classes have been isolated and identified from various parts of teak plants, such as barks, flowers, fruits, leaves and roots.