Allelochemicals and crop management : A review

ISSN: 2410-8790 Ashraf et al / Current Science Perspectives 3(1) (2017) 1-13 iscientic.org. www.bosaljournals/csp/ 2 editorcsp@bosaljournals.com supply (Arora et al., 2015). In general, allelopathy affected the growth and development of the neighboring plants by releasing the chemicals in the environment (Lux-Endrich et al., 2005). According to Rice (1984), allelopathy is the influence of one plant over the other plant by releasing the secondary metabolites or principle metabolic byproducts during different physiological process in its surrounding environment via leaching/decomposition, vitalization or root exudation thereby, affecting the growth of neighboring plant. Although secondary metabolites of plants are mostly associated with defense mechanism of plants but these valuable compounds can be involved in ecological functions. There is a strong evidence suggesting the involvement of metabolic compounds in communication of plants (Bertin et al., 2003; Weir et al., 2004). It was first time introduced by Molisch, an Austrian plant physiologist in 1937, who considered it chemical interaction among micro-organisms and plants (Hussain and Reigosa, 2011). It is a natural phenomenon in which different plants or organisms release the secondary metabolites to affect the function of other plants or organism in their positive or negative vicinity (Cheema et al., 2012; Farooq et al., 2011). These unique compounds, identified as allelochemicals, are flavonides, alkaloids, phenolics, momilactone, jasmonates, glucosinolates, hydroxamic acid, brassinosteriods, amino acids, terpenoids and carbohydrates (Adaramola et al., 2016; Asif, 2015a, b, c, d, e, f, 2016). These chemicals are nonnutritional and can be synthesized in any part of the plants i.e. roots, seeds, bark or leaves (Bonanomi et al., 2006; Rice, 1984). Allelopathy involves the synthesis of bioactive compounds capable of growth regulation, weed infestation control and pest management that resolve the problem of health defects and environmental pollution caused by ruthless use of synthetic chemicals (Dayan et al., 2009; Macías et al., 2007). Most of the studies asserted the inhibitory action of allelochemicals as well explored known dimension of allelopathy on the weed and pest management with the use of high concentrations of such chemicals (Farooq et al., 2009). Figure 1 depicts the importance of this hot issue that is the allelopathic application for the weed management Allelopathic crops, when used as smother crops, intercrops or green manure, mulch or cover crops can encounter biotic stresses. Thus, increasing the fertility of soil and reducing the erosion resulting in enhanced yield (Jabran et al., 2007; Khanh et al., 2005). This inhibitory action is attributed to interruption in various physiological process and blockage of important metabolitic within the plant (Iqbal et al., 2007). But some studies have been reported the promotory effect of allelochemicals when used in low concentrations especially foliar that imparts immunization against various abiotic stresses that improve the plant growth (Narwal, 2000). The foliar application of low concentration allelochemicals poses significant impact on crucial physiological process by improving cell elongation and cell division, photosynthesis etc. to enhance crop yield. Phytochemicals from plant extracts are innocuous to beneficial insects and grazing animals (Jamil et al., 2009), are easily degradable due to short half-life with no unnatural and toxic ring structures and low halogen substitution usually have different mode of action than dangerous synthetic agrochemicals (Cheema et al., 2009; Jabran et al., 2007; Jabran et al., 2010b; Kordali et al., 2009). Previous reviews and reports on application of allelochemicals in agriculture including importance of allelopathy in ecosystem (Khanh et al., 2005; Kruse et al., Fig. 1: Research publications on allelopathy as herbicide from 2000-2015 ISSN: 2410-8790 Ashraf et al / Current Science Perspectives 3(1) (2017) 1-13 iscientic.org. www.bosaljournals/csp/ 3 editorcsp@bosaljournals.com 2000; Rizvi et al., 1999), applications of allelopathy in fields for weed management (Bhowmik, 2003; Macías et al., 2007; Weston and Duke, 2003), applications of allelopathic crops as pesticides , suppression of weeds and crops through genetically different cultivars (Weston and Duke, 2003) has been discussed. In this review, identification of allelochemicals in allelophatic crops for the weed management is highlighted.