Endophyte mediated plant defence responses and their potential against pathogenic bacteria and fungi

Fungal and bacterial pathogens are major causes of crop diseases, responsible for over half of the global plant infections and reducing agricultural yields by 17–30% worldwide. Conventional management relies heavily on chemical pesticides, fungicides, and fertilizers, which, although effective in disease suppression, have led to serious environmental consequences, including soil acidification, groundwater contamination, and disruption of beneficial rhizosphere microbial communities essential for plant health. Endophytic microbes, which reside within plant tissues without inducing disease symptoms, represent a promising biological approach to disease management and crop improvement. Their direct defence mechanisms include the production of antimicrobial secondary metabolites, such as lipopeptides, alkaloids, polyketides, phenolics, and terpenoids, that disrupt pathogen cell membranes, inhibit spore germination, and block toxin biosynthesis. Additionally, endophytes produce siderophores to sequester iron, secrete hydrolytic enzymes to degrade pathogen cell walls, compete for nutrients and colonization niches, and engage in mycoparasitism, directly attacking phytopathogens. Indirect defence mechanisms involve the activation of plant immunity through systemic acquired resistance (SAR) mediated by salicylic acid and induced systemic resistance (ISR) regulated by jasmonic acid and ethylene signalling pathways. These pathways enhance defence enzyme production, reinforce cell walls, generate reactive oxygen species (ROS), and strengthen resistance against both biotrophic and necrotrophic pathogens. By combining pathogen suppression with immune priming, endophytes improve nutrient uptake, stress tolerance, and overall crop resilience, offering a sustainable alternative to chemical-based disease management strategies for enhanced agricultural productivity.