Bacteria in soil are essential for biogeochemical cycles and have been utilized for decades for crop production. The effects of bacterial interactions on plant health and soil fertility are determined in the rhizosphere. Plant growth-promoting rhizobacteria (Gray, Smith and biochemistry) are free-living bacteria that can promote plant growth by colonizing the plant root. PGPR is also referred to as Plant Health-Promoting Rhizobacteria (PHPR). They are associated with the rhizosphere, which is one of the most important soil ecological environments for plant microbes. Cyanobacteria that fix nitrogen symbiotically include Rhizobium, Bradyrhizobium, Azorhizobium, Allorhizobium, Sinorhizobium, and Mesorhizobium. Plant growth promoters that attach and colonize the root surfaces are free-living nitrogen-fixing bacteria, or association nitrogen fixer’s bacteria. These bacteria have the potential to contribute to the sustainability of plant growth. There are three main ways that the PGPR works: synthesizing specific compounds for the plants, facilitating the uptake of certain nutrients from the soil, and reducing or preventing disease. Plant growth promotion there are both direct and indirect ways to promote plant growth and development. Indirect plant growth promotion includes preventing phytopathogenic organisms from causing damage. In addition to producing siderophores, several bacterial species have also been found to synthesize antibiotics and control soil-borne pathogens. Hydrogen Cyanide (HCN) and/or enzymes capable of degrading fungal cell walls are another mechanism by which PGPR inhibits phytopathogens. There are two types of direct Plant Growth Promotion (PGPR): Symbiotic and non-symbiotic. Symbiotic PGPR generates plant hormones such as auxins, cytokines, gibberellins, ethylene and abscisic acid. Additionally, PGPR improves soil structure and organic matter content, enhances resistance to stress, stabilizes soil aggregates and helps solubilize mineral phosphates and other nutrients. By retaining more soil organic nitrogen and other nutrients in the plant-soil system, PGPR reduces the need for fertilizer N and P and enhances their release.
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