Allelochemicals: A source for developing economically and environmentally friendly plant growth regulators

Allelochemicals are specific secondary metabolites that can exhibit autotoxicity by inhibiting the growth of the same plant species that produced them. These metabolites have been found to affect various physical processes during plant growth and development, including inhibition of seed germination, photosynthesis, respiration, root growth, and nutrient uptake, with diverse mechanisms involving cell destruction, oxidative homeostasis and photoinhibition. In some cases, allelochemicals can also have positive effects on plant growth and development. In addition to their ecological significance, allelochemicals also possess potential as plant growth regulators (PGRs) due to their extensive physiological effects. However, a comprehensive summary of the development and applications of allelochemicals as PGRs is currently lacking. In this review, we present an overview of the sources and categories of allelochemicals, discuss their effects and the underlying mechanisms on plant growth and development. We showcase numerous instances of key phytohormonal allelochemicals and non-phytohormonal allelochemicals, highlighting their potential as candidates for the development of PGRs. This review aims to provide a theoretical basis for the development of economical, safe and effective PGRs utilizing allelochemicals, and emphasizes the need for further research in this area.