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Pseudomonas fluorescens

Pseudomonas fluorescens is a gram-negative, plant-growth-promoting rhizobacterium (PGPR) and biocontrol agent used in Indian agriculture against several soil-borne and foliar plant diseases, most notably rice sheath blight (Rhizoctonia solani) and root pathogens in vegetables and pulses.

Composition

  • Active organism: Pseudomonas fluorescens (gram-negative aerobic bacterium)
  • Reference strain bank: ICAR-NBAIR, Bengaluru, maintains and characterises strain collections used in commercial Indian formulations
  • Standard formulations:
  • Talc-based powder: minimum 1 x 10^8 CFU/g at sale; field counts at expiry of approximately 8 x 10^10 CFU/g have been reported
  • Liquid formulation: minimum 1 x 10^8 CFU/ml under the FCO liquid biofertiliser specification
  • Trade availability: multiple Indian brand names

Mode of action

The bacterium acts through four concurrent mechanisms: (a) antibiotic production, including 2,4-diacetylphloroglucinol (DAPG), phenazines and pyrrolnitrin, that suppress fungal pathogens; (b) siderophore (pyoverdin) production that sequesters iron and starves competing pathogens; (c) induced systemic resistance (ISR) in the host plant, priming defence pathways before infection; and (d) competition for nutrients and root surface in the rhizosphere. Some strains also produce IAA and ACC deaminase, which promote root growth.

Target use and dose

  • Seed treatment: 10 g powder per kg seed, or 10 ml liquid per kg seed.
  • Seedling root dip (paddy, vegetables): 10 g/L water for 30 minutes.
  • Soil application: 2-4 kg powder per acre, mixed with FYM, or 1 L liquid per 200 L water per acre.
  • Foliar spray: 5 g powder per litre at appearance of sheath blight symptoms.

It is the most widely used biocontrol agent for sheath blight in paddy across India.

Safety and regulatory status

Registered under the Insecticides Act (for biopesticide use) and FCO (for biofertiliser use); non-pathogenic to humans and most non-target organisms when strain identity is confirmed. Should not be tank-mixed with copper sprays or with broad-spectrum bactericides.

See also: Trichoderma Viride, Beauveria Bassiana, Metarhizium Anisopliae, Verticillium Lecanii, Microbial Biofertilizers, Liquid Organic Biofertilizer Consortia.

References

  1. Formulation Technology of Biocontrol Agents. Springer.
  2. Pseudomonas Biocontrol. Phytopathology (APS Journal).