Pathogen Biocontrol Using Plant Growth-Promoting Bacteria (PGPR): Role of Bacterial Diversity

Abstract

A vast microbial community inhabits in the rhizosphere, among which, specialized bacteria known as Plant Growth-Promoting Rhizobacteria (PGPR) confer benefits to host plants including growth promotion and disease suppression. PGPR taxa vary in the ways whereby they curtail the negative effects of invading plant pathogens. However, a cumulative or synergistic effect does not always ensue when a bacterial consortium is used. In this review, we reassess the disease-suppressive mechanisms of PGPR and present explanations and illustrations for functional diversity and/or stability among PGPR taxa regarding these mechanisms. We also provide evidence of benefits when PGPR mixtures, rather than individuals, are used for protecting crops from various diseases, and underscore the critical determinant factors for successful use of PGPR mixtures. Then, we evaluate the challenges of and limitations to achieving the desired outcomes from strain/species-rich bacterial assemblages, particularly in relation to their role for plant disease management. In addition, towards locating additive or synergistic outcomes, we highlight why and how the benefits conferred need to be categorized and quantified when different strains/species of PGPR are used in combinations. Finally, we highlight the critical approaches needed for developing PGPR mixtures with improved efficacy and stability as biocontrols for utilization in agricultural fields.

Enhancing systemic resistance in faba bean (Vicia faba L.) to Bean yellow mosaic virus via soil application and foliar spray of nitrogen-fixing Rhizobium leguminosarum bv. viciae strain 33504-Alex1

“…Hence, foliar treatment is more logical for infected plants ( Chandrashekar et al, 2018 ). The PR-1 and PR-5 gene expression are regulated by salicylic acid (SA), which is the primary mediator of the systemic acquired resistance (SAR) mechanism ( Breen et al, 2017 ; Wang et al, 2021 ). Thus, the results showed that 33504-Alex1 could boost SA-mediated SAR in faba bean when infected with BYMV.…”

Advances in Soil Engineering: Sustainable Strategies for Rhizosphere and Bulk Soil Microbiome Enrichment

“…Stenotrophomonas rhizophila strain SR80 enhanced wheat growth, both below and above ground, and induced strong disease resistance by boosting plant defence in the above-ground plant parts when the pathogen Fusarium pseudograminearum was present [148]. But there are several strains described with beneficial effects proved in cereals, such as wheat, rye or rice, as well as in other cultures such as barley, tomato, cucumber, pepper or Chinese cabbage (see reviews [43,72,149,150]). Organic amendments can also be supplemented with PGPB, and their effects on plants extended even further when compared to controls.…”

Mechanism of Antagonistic Bioagents in Controlling Root-Knot Nematodes (Meloidogyne sp.): A Review

“…In phenazine-producing Pseudomonas, this quorum-sensing mechanism is well understood. Plant growth secreted toxin surface chemicals (bio-surfactants) and volatiles, chitinase cell wall-degrading enzymes, and -1,3glucanase enhancing rhizobacteria to reduce soil-borne pathogens [154][155][156]. The release of siderophore ligands, which efficiently grab iron and inhibit pathogen development, was previously identified as a biocontrol mechanism [157,158].…”