Plant Growth-Promoting Rhizobacteria (PGPRs): The “A” Team

If you think mycorrhizal fungal spores are small, let’s turn our microscope to 100 times magnification to see our next players. As the title eludes to, PGPRs are microscopic unicellular bacteria that colonize roots and stimulate plant growth. These are nitrogen-fixing bacteria that convert soil-bound elemental nutrients into a form that plants can use. Consider them the key-holder to your bank safe. When you need to pull money out of your safe, you have to call upon a banker to unlock it for you. Similarly when a plant is in need of nutrients like nitrogen, phosphorous and potassium that is fixed in soil and bedrock, it relies on the metabolic pathways of rhizobacteria to free-up these ions and convert them into a currency that the plant can accept.

Azos-treated tomato roots established in a cloning machine.

Bacterial species belonging to the Azotobacter and Azospirillum genera are widely used in agricultural trials. Several strains have gained importance; along with their nitrogen-fixing ability they also enhance plant growth by producing phytohormones, chemicals that regulate growth. Application of Azotobacter chroococcum and Azospirillum brasilense inoculants in agriculture, especially in cereals, has resulted in notable increases in crop yields.