Allelopathy and the Role of Allelochemicals in Plant Defence

Allelopathy is described as the interference to plant growth resulting from chemical interactions among plants and other organisms mediated through release of plant-produced bioactive secondary metabolites referred to as allelochemicals. A number of mechanisms have been studied for the release of allelochemicals from various plant tissues including volatilization or leaching from aerial parts, exudation from roots and decomposition of plant residues in soil. Despite differences in biological activity and mode of action, related compounds commonly share similar biosynthetic pathways while some classes of metabolites can be produced using diverse biosynthetic pathways. Recently considerable research has also been undertaken to critically understand the role of allelochemicals in plant succession and plant invasion in native and nonnative ecosystem. In addition, numerous studies have been performed on the selection and utilization of weed suppressive crops and their residues for weed management in sustainable agriculture systems. A better understanding of allelochemical production with respect to plant defence strategies, both physical and chemical, may also allow us to better protect and manage developing crops, limit the spread of invasive weeds, preserve native plant stands and create strategies for allelochemical development and application as novel pesticides. The use of sensitive analytical techniques associated with performance of metabolomics in concert with other omics technologies has led to new advances in the identification of unique allelochemicals, the biosynthetic pathways associated with their production, their complex role(s) in the soil rhizosphere and their production as impacted by a changing climate. Identification of novel plant metabolites, including allelochemicals, may result in a source of biologically based pesticides through the provision of complementary structures for future synthesis and as an aid in the development of new molecular target sites.