Principle, diversity, mechanism, and potential of practical application of plant probiotic bacteria for the biocontrol of phytopathogens by induced systemic resistance

Abstract Phytopathogens are the major threat to food and nutritional security of the ever-increasing population of the world. Plant probiotic bacteria (PPB) exert multiple beneficial functions to protect host plants from phytopathogens through various mechanism including induced systemic resistance (ISR) to the pathogen. Application of an elite strain or a consortium of PPB to protect plants from disease-causing microorganisms is an eco-friendly option approach for sustainable agriculture. The PPB modulates plant physiology and signaling pathways linked to defense against pathogens by regulating the expression of host genes. The underlying molecular mechanisms involved in beneficial effects of PPB to host have partly been understood. As a result, field application of these biologicals is still limited due to inconsistency in their efficacy. Some PPB can trigger salicylic acid (SA)-dependent systemic acquired resistance (SAR) pathway by producing SA whereas many others trigger different signaling pathways independent of SA. Major PPB genera Pseudomonas, Bacillus, Serratia, Paraburkholderia, Delftia have multiple beneficial functions including eliciting ISR in the host and useful for biorational management of phytopathogens. This chapter comprehensively reviews the principle, diversity, mechanisms of action, and potentials of practical application of PPB for biocontrol phytopathogens predominantly through ISR.