Mechanism of Action of Allelochemicals

Allelopathy could be characterized as “an imperative component of plant impedance interceded by the addition of secondary metabolites produced by plants into the soil rhizosphere” (Weston, 2005). These secondary metabolites are typically exuded into the rhizosphere and affect the development of plants that are growing in the vicinity of allelopathic plants (Akemo, Regnier, & Bennett, 2000). Chemical compounds that inflict allelopathic impacts are called allelochemicals or allelochemics, which are by and large considered to be those chemical groups, for example, alkaloids, flavonoids, glucosinolates, phenolics and terpenoids (Reigosa, Souto, & Gonz, 1999). Natural products recognized with allelopathic potential have been classified into the following groups: (a) cytotoxic gases, (b) organic acids, (c) aromatic acids, (d) simple unsaturated lactones, (e) coumarins, (f) quinones, (g) flavonoids, (h) tannins, (i) alkaloids, and (j) terpenoids and steroids (Mushtaq & Siddiqui, 2018). Allelopathy has been well documented for many great years (Rice, 1984), however, the understanding of the mechanisms of the mode of action of allelochemicals stays darken (Mohamadi & Rajaie, 2009). Several biosynthetic pathways are responsible for the production of the various classes of these chemical compounds, though they are not necessary for primary processes of growth and reproduction for the allelopathic species (Pagare, Bhatia, Tripathi, Pagare, & Bansal, 2015). However, these compounds can influence plant development indirectly by modifying the interspecific competition for the plants in association (Abhilasha, Quintana, Vivanco, & Joshi, 2008). A wide array of these compounds are known today, however, just a limited number has been recognized as allelochemicals (Mushtaq & Siddiqui, 2018; Rice, 1984). Allelochemicals are predominantly present throughout the plant including leaves, stems, roots, rhizomes, inflorescence, pollen, fruits and seeds (An, Pratley, & Haig, 1998). The production of allelochemicals in a plant species may vary spatially and over time scale; Singh, Jhaldiyal, and Kumar (2009) found foliar and leaf litter leachates of Eucalyptus species more lethal than its bark leachates to some commercial crops.