Plant growth promoting rhizobacteria are the soil bacteria that colonized plant root and facilitate the plant growth directly or indirectly. It increases the global dependence on hazardous agricultural chemicals. They are characterized as stimulating plant growth through mobilizing nutrients in soils, proficient to colonize the root surface and survive multiply and
compete with other microbiota and it promotes plant growth.
Classification based on their functional activities as
- Act as a Biofertilizers
TYPES OF PGPR
Existing in the rhizosphere, on the rhizoplane, or in the spaces between cells of the root cortex. e.g: Agrobacterium, Arthrobacter, Azotobacter, Azospirillum, Bacillus, Burkholderia, Caulobacter, Chromobacterium, Erwinia, Flavobacterium, Micrococcus, Pseudomonas, and Serratia.
Intracellular (iPGPR )
Bacteria residing inside plant cells, producing nodules, and being localized inside those specialized structures e.g: Allorhizobium, Azorhizobium, Bradyrhizobium, Mesorhizobium.
BIO-CONTROL PROPERTIES OF PGPRS
Biocontrol is a process through which a living organism limits the growth or propagation of undesired organisms or pathogens.’’
- Competition for nutrients
- Displacing pathogens
IMPORTANCE OF PGPR IN AGRICULTURE
- Increased health and productivity of different plant species under both normal and stressed conditions.
- The plant-beneficial rhizobacteria may decrease the global dependence on hazardous agricultural chemicals that destabilize the agro-ecosystems.
- The rhizobacteria play role in recycling the soil nutrients and consequently, they are crucial for soil fertility.
- Novel traits like heavy metal detoxifying potentials, pesticide degradation/tolerance.
- Salinity tolerance and biological control of phytopathogens and insects.
HARMFUL ASPECTS OF PGPR
- Cyanide acts as a growth inhibitor for some plants
- High levels of auxin inhibit root growth
- Rhizobitoxine produced by Bradyrhizobiumelkanii may hurt nodulation
- Rhizobitoxine can also induce foliar chlorosis in soybeans.
FUTURE RESEARCH AND DEVELOPMENT STRATEGIES
- Future research in rhizosphere biology will rely on the development of molecular and biotechnological approaches to increase our knowledge of rhizosphere biology and to achieve integrated management of soil microbial populations.
- Fresh alternatives should be explored for the use of bioinoculants for other high-value crops such as vegetables, fruits, and flowers.
- The application of multi-strain bacterial consortium over single inoculation could be an effective approach for reducing the harmful impact of stress on plant growth.