Role of nonpathogenic fungi in inducing systemic resistance in crop plants against phytopathogens

Abstract

Plants are surrounded by a plethora of microorganisms, including fungal strains. Fungi associated with plants are known to exert their beneficial effects by helping them in absorption of water and nutrients and protecting them against harmful microorganisms. Protective effect is generally mediated by performing antagonistic action on pathogens and pests. However, along with their direct effects, they have been shown to trigger defense responses in plants against various pathogenic species, including members of bacterial, fungal and viral groups. This type of resistance mechanism triggered by nonpathogenic microorganisms is termed as induced systemic resistance (ISR) and has been observed in several strains of fungi. Some of the important nonpathogenic fungal strains found to induce ISR in crop plants include mycorrhiza, Trichoderma sp., Penicillium sp., Fusarium sp., Phoma sp., etc. They have been shown to trigger defense responses via multiple signaling pathways involving salicylic acid, jasmonic acid or ethylene. Candidate signaling molecules, also known as elicitors, have been recently identified, particularly from Trichoderma sp. and shown to protect the plants from pathogens. Thus, with respect to their role in ISR, this chapter highlights the potential of nonpathogenic fungal strains in controlling plant diseases.