Abstract

In view of urgent need to improve plant growth and increase productivity, the factors affecting plant growth are studied. Since the nutrients around the root are abundant, they support the growth of the organisms around them. Among these organisms, especially the bacterial community, there is a group known as the root bacteria that occupies the rhizosphere, causing a direct stimulation of plant growth or control biology of plant pathogens, it has a common name “Plant Growth-Promoting Rhizobacteria (PGPR). These bacteria contribute to many plant activities, due to the capabilities known to them related to plant activities. These bacteria are characterized by nitrogen fixation and can dissolve phosphorus, iron and others, in addition to improving plant tolerance of some heavy elements. Some strains of plant growth stimulating root bacteria to build some plant growth regulators such as auxin, gibberellin, cytokinin, and ethylene, or produce volatile compounds, so these may contribute to stimulating growth. PGPR affect the photosynthesis system by increasing some plant pigments. Some strains of these bacteria have been known to form antagonistic compounds to certain pathogens such as phenazine, thus protecting plants or increasing plant resistance to Systemic Acquired Resistance (SAR). Some strains have been used as biofertilizers as inoculants or co-inoculants. There is no general agreement on the mechanism of action, the most important is the improvement of selection of inoculants and their quality for a specific need as the effectiveness of selecting PGPR is crucial for this biotechnology, especially increasing the yield of plants.

Keywords:Bacteria; Roots stimulating plant growth; Dissolving phosphorous; Growth regulators; Nitrogen fixation; Biological fertilizers