Plant growth-promoting rhizobacteria (PGPR): their potential as antagonists and biocontrol agents

TLDR

Plant growth‑promoting rhizobacteria (PGPR) are root‑colonizing bacteria that enhance plant growth and can suppress pathogens through antimicrobial compounds and induced systemic resistance. This review examines PGPR as biocontrol agents and explores their potential in developing inoculants that combine antagonistic and resistance‑inducing mechanisms. PGPR suppress pathogens by local antagonism or by triggering systemic resistance through salicylic acid‑dependent SAR or jasmonic acid/ethylene‑mediated ISR pathways.

Abstract

Bacteria that colonize plant roots and promote plant growth are referred to as plant growth-promoting rhizobacteria (PGPR). PGPR are highly diverse and in this review we focus on rhizobacteria as biocontrol agents. Their effects can occur via local antagonism to soil-borne pathogens or by induction of systemic resistance against pathogens throughout the entire plant. Several substances produced by antagonistic rhizobacteria have been related to pathogen control and indirect promotion of growth in many plants, such as siderophores and antibiotics. Induced systemic resistance (ISR) in plants resembles pathogen-induced systemic acquired resistance (SAR) under conditions where the inducing bacteria and the challenging pathogen remain spatially separated. Both types of induced resistance render uninfected plant parts more resistant to pathogens in several plant species. Rhizobacteria induce resistance through the salicylic acid-dependent SAR pathway, or require jasmonic acid and ethylene perception from the plant for ISR. Rhizobacteria belonging to the genera Pseudomonas and Bacillus are well known for their antagonistic effects and their ability to trigger ISR. Resistance-inducing and antagonistic rhizobacteria might be useful in formulating new inoculants with combinations of different mechanisms of action, leading to a more efficient use for biocontrol strategies to improve cropping systems.