Screening the Allelopathic Activity of 14 Medicinal Plants from Northern Thailand

Allelopathy is a phenomenon of chemical interactions among plants, and allelochemicals are chemicals released from one plant into the environment via volatilization, root exudation, leachates, and plant decomposition. The allelochemicals influence the germination and growth of neighboring plants in either an inhibitory or stimulatory manner (Rice, 1984). In recent years, allelochemicals have been studied and tested as bioherbicides for weed control. Medicinal plants have been widely studied in the search for potential natural active compounds (Batish et al., 2007; Gilani et al., 2010). The allelopathic activity of 239 medicinal plants was evaluated and 223 were found to have allelopathic activities (Fujii et al., 2003). The allelopathic activity of numerous medicinal plants has also been reported (Syed et al., 2014; Synowiec and Nowicka-Po e , 2016). Thailand is located in Southeast Asia and has a tropical climate, resulting in a wide diversity of plant species. About 80% of at least 10,000 forest tree and herbal plant species in Thailand are recognized for their medicinal properties (Thitiprasert et al., 2007). Many of the species dominate and form colonies with few or no other plant species around them. Their strong ability to garner natural resources such as nutrients and water may allow them to establish colonies. Their allelopathic ability may also be involved in establishing colonies. The selected 14 Thai medicinal plants in this study are common plants in northern Thailand and grow as colonies in nature. All of them have important medicinal properties, but rarely study in allelopathic activity. The present study, therefore, aimed to evaluate the allelopathic activity of 14 Thai medicinal plants on the seedling growth of lettuce for the purpose of developing natural herbicides in the future.