Endophytes: Role and functions in crop health

Abstract

Plant-microbe interactions is an important concept, and the significance of these interactions on sustainable agriculture is enormous. These interactions can be neutral, commensal, mutualistic, saprophytic, or harmful. Endophytes are beneficial microbes that reside and establish symbiotic relationships with the plants. These beneficial microbes are of either bacterial, fungal, or actinomycete origin. A wide array of beneficial effects are reported with endophytic associations in plants that include bioremediation, herbivory, induced resistance, plant growth promotion, and pest and disease management. Nomenclature of endophytes is generally according to the plant tissue it harbors, such as endophytes of root, shoot, leaf, seed, etc. Our review presents different bacterial and fungal endophytes in plants and their role in improving crop health. The plant growth- promoting (PGP) activities of these endophytes such as production of growth hormones like indoleacetic acid (IAA), gibberellic acid (GA), and cytokinins and phosphate solubilization in different crops by specific endophytes are discussed in detail. Further, specific antagonistic activities of endophytes like induced systemic resistance; production of salicylic acid, siderophores, HCN, cell walldegrading enzymes, and antimicrobial metabolites including antibiotics; and direct antagonism against different plant pathogens are thoroughly discussed. The preferences of endophytes to different plant parts; their different niches such as roots, shoots, leaves, and whole plants; and specific antagonistic and PGP activities are elaborated in detail. Other beneficial activities such as herbivory, bioremediation, biodegradation, and biofertilization including nitrogen fixation are also discussed briefly. Finally, we have also discussed the scope and future prospects of endophytes in improving soil and crop health.