Induction of Systemic Resistance for Disease Suppression

Abstract

Plant growth promoting rhizobacteria (PGPR) are extensively studied for their antagonistic effect on soil microbes and their induction of systemic resistance towards root and foliar pathogens. Induced resistance tends to increase basal resistance in host in order to provide broad spectrum protection against a wide array of pathogens in nature. A large number of Pseudomonads and Bacillus spp. have been identified with the potential to induce systemic resistance in various hosts. While certain strains result in induced resistance in a wide host range, some show specificity indicating specific plant--microbe interactions. Induced systemic resistance (ISR) is induced by PGPR through secreted determinants. Determinants such as lipopolysaccharides, siderophores, antibiotic, and enzymes have been reported to effectively elicit ISR in host. ISR signals are transmitted locally and systemically. In ISR, jasmonate (JA) and ethylene (ET) regulate the signal transduction for induction while salicylic acid (SA) remains crucial in the transduction of systemic acquired resistance (SAR). Although ISR and SAR both elicit induced responses in host, their signals, signaling pathways, and genes activated vary. Hence JA/ET-induced defense-related genes will be activated in ISR, and SA-dependent defense genes will be activated in SAR. These genes are effective on different sets of pathogens (necrotrophs and biotrophs). Both mechanisms contribute towards the protected nature of the host. In this chapter, the mechanisms, pathways, signals, importance, similarities, and dissimilarities of both these systems are elaborated.