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Plant growth promoters in Rice


Plant growth promoters (PGPR)

  • Pathogenic microorganisms affecting plant health are a major and chronic threat to food production and ecosystem stability worldwide.
  • Increasing use of chemical inputs causes several negative effects: development of pathogen resistance to the applied agents and their nontarget environmental impacts.
  • There are also a number of fastidious diseases for which chemical solutions are few, ineffective or nonexistent.
  • Biological control is thus being considered as an alternative or a supplemental way of reducing the use of chemicals in agriculture.
  • Micro-organisms that can increase plant growth and productivity are termed as Plant Growth Promoting Rhizo- micro-organisms.
  • Kloepper and Schrotnh (1978) and Kloepper et al., (1980) coined the term PGPR.
  • Bashan and Holguin (1998) -
       (a) Biocontrol plant growth promoting Bacteria (Biocontrol PGPB)

       (b) Plant growth promoting Bacteria (PGPB)

Sources of Plant Growth Regulation Substances

     (a) Higher plants which are capable of synthesizing all five major classes of PGRS

     (b) Rhizosphere micro-organisms.

5 Classes of PGRS

  1. Auxins
  2. Gibberllins
  3. Cytokinins
  4. Abscisic Acid
  5. Ethylene

Plant Growth Promoting Rhizobacteria

  • Azotobacter
  • Azospirillum
  • Arthrobacter
  • Burkholderia
  • Enterobacter
  • Klebsiella
  • Pseudomonas fluroscens
  • Pseudomonas putida
  • Bacillus subtilis
  • Serratia


Direct Influence

  • Increased solubulization and uptake of nutrients.
  • Production of plant growth promoting substances.

Indirect Influence

  • Suppression of pathogens through antibiotics, bacteriocin production.
  • Production of siderophores and other secondary metabolites.
  • Induction of phytoalexins or systemic disease resistance in plants.

Bio-control: "Reduction in pathogen inoculum, its disease producing capacity by action of one or more organisms accomplished naturally or through manipulation of environment, host or antagonist / by mass introduction of one or more antagonists".

Advantages of Biocontrol agents:

  • Harmless to beneficial organisms.
  • Environmentally safe.
  • Reduces dependence on chemical pesticides.
  • Lack of development of pathogen resistance.
  • Compatibility with several pesticides.
  • Lack of danger to human beings and animals.
  • Improve soil health and enhance agricultural sustainability.
  • Production of plant growth promoting substances.
  • Can play a key role in integrated disease management.

 Factors Involved In Biological Control

  • Host
  • Environment
  • Bio-control Agent
  • Pathogen


 Mode of action of Bio-logical control agents include

  • Antibiosis
  • Competition for iron
  • Competition for colonization sites and nutrients.
  • Induced resistance
  • Inactivation of pathogen germination facto
  • Degradation of pathogenecity factors
  • Parasitism

Mycorrhizal symbiosis:

    Mycorrhizae involve a unique symbiotic association between plant roots and infecting fungi.

  • Production of plant growth regulating substances.
  • Enhanced uptake of nutrients
  • Resistance to drought and salinity Increased tolerance to pathogens

Mechanisms of plant disease control by Mycorrhizal fungi

  • Creating a mechanical barrier for the pathogen penetration and subsequent spread.
  • Thickening of cell wall through lignifications and production of other polysaccharides.
  • Stimulating the host roots to produce and accumulate sufficient concentration of metabolites.
  • Increasing the concentration of Ortho-di-hydroxy phenols in roots.
  • Producing antifungal and antibacterial antibiotics.
  • Competing with the pathogens for the uptake of essential nutrients in the Rhizosphere and at root surfaces.
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