Comparative Study on Allelopathic Potential of Medicinal Plants Against the Growth of Cress and Barnyard Grass

Abstract

In conventional agriculture, the use of synthesis herbicides is still recognized as an effective tool to eliminate weeds and to promote the highest possible yield of crops (Norsworthy et al., 2012; Kniss, 2017). On the other hand, the overuse of synthetic herbicides negatively affects both the environment and human health, and increases the number of herbicide-resistant weeds (Aktar et al., 2009; Staley et al., 2015). Also, increasing consumer awareness of herbicide residues in production practices leads to increased demand for organic products or safer foods (McErlich and Boydston, 2013; Tal, 2018). To overcome these problems, reducing the reliance on synthetic herbicides and shifting to sustainable agriculture is needed. Organic farming is a feasible alternative agricultural practice that relies on an integrated natural-based system (Gomiero et al., 2011; IFOAM EU Group, 2016). In this direction, using natural plant products and allelopathy for weed management is gaining attention (Singh et al., 2003). Additionally, using natural substances including plant extracts is considered safe and acceptable in organic farming (Brandt, 2007; Verhoog et al., 2007; Jespersen et al., 2017). Allelopathy is a biological phenomenon in which plants release secondary metabolites (allelochemicals) that inhibit or stimulate the growth, development, and reproduction of other organisms in the environment (Rice, 1984; Einhellig, 1995). Such secondary metabolites or natural compounds could be considered as a possible alternative strategy for weed management (Bhadoria, 2010; Tesio and Ferrero, 2010). It is generally known that medicinal plants synthesize and accumulate a large amount of natural bioactive compounds, which provide a vital role in many biological activities (Silva and Fernandes Júnior, 2010; Yang et al., 2016). Numerous medicinal plants have been studied for potential allelopathic properties. Fujii et al. (1991) surveyed Japanese medicinal plants to determine their allelopathic properties. They also conducted further screening of 239 medicinal plant species for their allelopathic activity (Fujii et al., 2003). Many natural active compounds have also been isolated from other medicinal plants and reported as allelochemicals (Lin et al., 2004; Pukclai et al., 2010; Kato-Noguchi et al., 2014; Suwitchayanon et al., 2017a; 2017b; Boonmee et al., 2018a; 2018b). Thailand is located in the biologically complex Asia Pacific region. This vast area has diverse eco-climates and physiography, resulting in wide varieties of plant species as well as medicinal plant varieties that may have the potential to provide natural active substances (Arora, 2014; Hughes, 2017). Hence, screening of medicinal plants with allelopathic properties is the first step to investigate the potentiality of the plant to control weeds. This study, therefore, aimed to evaluate the allelopathic potential of aqueous methanol extracts from 12 Thai medicinal plants against the growth of representative test plants (broadand narrow-leaved), for further isolation and identification of allelopathic substances.