Endophytes as Guardians of Plants Against Diseases

Abstract

A huge number of different microbes are resident of interior parts of the plants which are collectively known as endosphere microbiome of the plants. There are different classes of these endophytes which are primarily bacterial and fungal organisms. Some of them are endophytic to the aboveground parts of the plants, while many are endophytic to the roots. Several biotic and abiotic factors affect the occurrence and diversity of these endophytes. These endophytic microbes have developed very vital symbiotic relationship with the plants and are involved in a variety of physiological functions. For instance, different endophytic microbes act antagonistically against several plant pathogens and are involved in the activation of plant defense responses. They act as guardians of the plants against diseases by growth promotion through nitrogen fixation, nutrient mobilization, iron sequestration, and synthesis of ACC deaminase and induction of various phytohormones. Similarly, these antagonistic microbes could directly defend the plants against pathogens through production of secondary metabolites, ROS, antimicrobial compounds, allelochemicals, and toxins. Moreover, these endophytes induce siderophore production, activate induced systemic resistance, and are involved in biosynthesis of antibiotics and proteolytic enzyme to directly control the plant pathogens. This chapter elaborates various classes of endophytes and mechanisms involved in the antagonism employed by different endophytes against various plant pathogens.