Azospirillum

Introduction

Azospirillum is a genus of plant growth-promoting rhizobacteria (PGPR) widely applied in sustainable agriculture. These microbes are known for their ability to enhance crop yields by fixing atmospheric nitrogen, producing phytohormones, and improving root architecture. As climate-smart agriculture becomes essential, Azospirillum offers a low-input, eco-friendly solution to increase productivity and plant resilience under stress conditions.

Scientific Description

Azospirillum spp. are gram-negative, motile, microaerophilic bacteria belonging to the family Rhodospirillaceae. They colonize the rhizosphere of grasses and cereals, forming loose associations with root surfaces (non-nodulating). The genus includes species such as Azospirillum brasilense, Azospirillum lipoferum, and Azospirillum amazonense, among others.

Key functional traits:

• Biological Nitrogen Fixation (BNF): Uses nitrogenase enzyme to fix atmospheric nitrogen into ammonia.
• Phytohormone Production: Produces indole-3-acetic acid (IAA), gibberellins, and cytokinins.
• Siderophore Production: Enhances iron acquisition in nutrient-poor soils.
• Stress Tolerance Induction: Triggers antioxidant enzymes in plants under drought or salinity.

Benefits

• Nitrogen Fixation: Supplements synthetic fertilizers by converting atmospheric nitrogen into plant-usable forms.
• Improved Root Growth: Stimulates root elongation and branching, improving nutrient uptake.
• Enhanced Germination and Growth: Promotes early seedling vigor and uniform plant establishment.
• Increased Yield and Biomass: Contributes to higher productivity across various crop species.
• Improved Water Use Efficiency: Helps plants cope better under water-stressed conditions.
• Better Soil Microbiome Balance: Supports other beneficial soil microbes and suppresses some pathogens.

Uses

• Crops: Widely used on cereals (rice, wheat, maize), millets, sugarcane, sorghum, and legumes.
• Formulation Types: Available as liquid cultures, seed coatings, or soil inoculants.
• Application Methods:
  • Seed treatment (2-5 ml/kg seed)
  • Soil application (1–2 L/acre)
  • Foliar sprays in combination with other bio-inputs

Trivia

• First isolated in the 1970s in Brazil from tropical grasses.
• Known for associative symbiosis rather than root nodule formation.
• Compatible with mycorrhizal fungi and Trichoderma in co-inoculant blends.
• Plays a role in regenerative agriculture and organic farming certifications.