The Role of 2,4-Diacetylphloroglucinol- and Phenazine-1-Carboxylic Acid-Producing Pseudomonas spp. in Natural Protection of Wheat from Soilborne Pathogens

Abstract

Plant growth-promoting bacteria (PGPB) facilitate plant growth in two ways, either by direct stimulation or by biocontrol (i.e., suppressive activity against soil-borne diseases). The direct stimulation of plant growth may be a consequence of nitrogen fixation, phosphate solubilization, iron sequestration, synthesis of phytohormones (such as auxins, cytokinins, and gibberellins), or modulation of plant ethylene levels. The biocontrol activity of PGPB is typically a consequence of the ability of the bacteria to synthesize antibiotics, fungal cell wall degrading enzymes such as chitinase, siderophore activity, or induction of systemic resistance within the plant. Any particular PGPB may possess one or several of these activities. This review presents an overview of the fundamental mechanisms that PGPB utilize to facilitate plant growth, emphasizing recent developments in this field. The rationale for examining these basic mechanisms in detail is that the understanding gained through such an endeavor should ensure that the subsequent use of these organisms in the field, in agriculture, horticulture, and environmental cleanup, is both efficacious and highly reproducible.