Phytostimulating Mechanisms and Bioactive Molecules of Trichoderma Species: Current Status and Future Prospects

Abstract

Ever-increasing pressure on the agricultural land due to various biotic and abiotic stresses made agriculture a nonprofitable venture. In order to bring back the lost glory to agriculture, there is an urgent need to reclaim this eroded agriculture with sustainable practices, one among them is the use of plant growth-promoting microorganisms such as rhizosphere-competent Trichoderma sp. In this chapter, the major mechanisms and bioactive molecules involved in plant growth promotory activity of Trichoderma sp. are described in detail. Trichoderma sp. is also known to produce growth-regulating phytohormones and other bioactive molecules which are known to protect them against antimicrobial compounds secreted by plant, but they also help the plants in overcoming various stresses. Various hydrolytic enzymes such as chitinases, glucanases, and proteinases are produced by Trichoderma which aid in its mycoparasitic response. The fungus is also able to enhance plant growth through nutrient solubilization and its uptake. It mobilizes phosphates from fixed organic/inorganic phosphorus sources through both enzymatic (phosphatases, phytases) and nonenzymatic mechanisms (production of organic acids and siderophores). Trichoderma produces a wide array of secondary metabolites and volatile compounds which are mainly responsible for its biocontrol action. Suppression of fungal plant pathogens through mycoparasitism involves signal transduction and G protein signaling in Trichoderma. Secondary metabolites and volatile compounds produced by this fungus are very diverse in their occurrence and mode of action against phytopathogens. Recent developments in molecular biology, metabolomics, and proteomics have opened an insight for the use of secondary metabolites as biopesticides rather than the application of whole organisms.