Agronomic Applications of Azospirillum and Other PGPR

The rhizosphere is the area of soil influenced by plant roots. Bacteria that are known to promote plant growth and have good potential to be commercially applied are generally denominated as PGPR (plant growth promoting rhizobacteria). Important effects of inoculation with PGPR on root morphology are consistent with the exogenous indole-acetic acid (IAA) levels secreted mainly in the case of Azospirillum. Extensive field inoculation experiments with A. brasilense clearly show an average significant increase in crop yield of maize, wheat, sorghum, and other forage grasses. There has been a surge in the inoculation practice with commercial formulations mainly in the MERCOSUR, with estimations of about 2–2.5 million doses used in 2012 in Brazil, mainly in maize. Dual inoculation of rhizobia and Azospirillum in legumes results in increased production of plant flavonoids and enhanced capacity to induce Rhizobium nod-gene expression. In order to ensure permanent adoption of the technology, it is necessary to have coordinated multidisciplinary research to provide technical bases for inoculant formulation and application, and to have a regulatory framework setting high standards to assure inoculant quality in the market.