SYSTEMIC RESISTANCE INDUCED BY RHIZOSPHERE BACTERIA

TLDR

Nonpathogenic rhizobacteria trigger a systemic resistance in plants that resembles pathogen‑induced SAR, has been shown against fungi, bacteria, and viruses in multiple species, and varies in effectiveness depending on bacterial strain and host plant, with no consistent host changes but faster and stronger responses upon pathogen challenge. Key ISR determinants include lipopolysaccharides, siderophores, and salicylic acid, and while some rhizobacteria activate the SA‑dependent SAR pathway, others require jasmonic acid and ethylene perception for ISR to develop. ISR functions effectively under field conditions and provides a natural biological control strategy for plant disease.

Abstract

Nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Rhizobacteria-mediated induced systemic resistance (ISR) has been demonstrated against fungi, bacteria, and viruses in Arabidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathogen remained spatially separated. Bacterial strains differ in their ability to induce resistance in different plant species, and plants show variation in the expression of ISR upon induction by specific bacterial strains. Bacterial determinants of ISR include lipopolysaccharides, siderophores, and salicylic acid (SA). Whereas some of the rhizobacteria induce resistance through the SA-dependent SAR pathway, others do not and require jasmonic acid and ethylene perception by the plant for ISR to develop. No consistent host plant alterations are associated with the induced state, but upon challenge inoculation, resistance responses are accelerated and enhanced. ISR is effective under field conditions and offers a natural mechanism for biological control of plant disease.