PGPR, or Plant Growth-Promoting Rhizobacteria, refer to a group of bacteria that colonize the rhizosphere (the area surrounding the roots) of plants and exert beneficial effects on plant growth and development. These beneficial bacteria play a crucial role in sustainable agriculture by promoting plant growth and enhancing plant health through various mechanisms.
One of the primary mechanisms by which PGPR promote plant growth is through the production of phytohormones, such as auxins, cytokinins, and gibberellins. These hormones stimulate root growth, shoot elongation, and overall plant biomass production. Additionally, PGPR can solubilize phosphates and other essential nutrients, making them readily available for plant uptake, thereby enhancing nutrient acquisition and utilization.
PGPR also contribute to plant growth by producing siderophores, which are iron-chelating compounds that help plants acquire iron from the soil. Iron is an essential micronutrient for plants, and its deficiency can lead to chlorosis and stunted growth. By facilitating iron uptake, PGPR ensure proper plant development and overall vigor.
Another important mechanism by which PGPR benefit plants is through the production of various enzymes and metabolites that can suppress the growth of plant pathogens. These bacteria can produce antibiotics, hydrogen cyanide, and other compounds that inhibit the growth of phytopathogenic fungi, bacteria, and nematodes, thereby protecting plants from diseases and improving their overall health.
PGPR can also induce systemic resistance in plants, a phenomenon known as induced systemic resistance (ISR). ISR is a physiological state of enhanced defensive capacity against a broad spectrum of pathogens and pests. PGPR trigger this response by interacting with plant receptors, leading to the activation of defense-related genes and the production of antimicrobial compounds, fortifying the plant's immune system.
Furthermore, PGPR can contribute to plant growth by producing enzymes that degrade organic matter, such as cellulose, lignin, and chitin, thereby releasing nutrients that can be taken up by plants. This process is particularly important in nutrient-poor soils, where the availability of essential nutrients may be limited.
The use of PGPR as biofertilizers and biocontrol agents in agriculture has gained significant attention in recent years due to their potential to reduce the reliance on chemical fertilizers and pesticides, which can have adverse environmental impacts. PGPR-based products are considered environmentally friendly and sustainable alternatives to conventional agricultural practices, promoting plant growth while minimizing the negative effects on soil health and ecosystems.
3. Introduction
Microorganisms such as PGPR, mycorrhizal fungi, and endophytes play important roles in
promoting plant growth and health
They can also produce siderophores, generate phytohormones, and synthesize stress-relieving
enzymes
Endophytic organisms also produce exopolysaccharides (EPS) that alleviate their attachment to
the surface of the root and prevent bacterial cells from oxidative damage
4. Molecular Crosstalk and Signalling Pathways
Plant hormone pathways interact with each other in a complex network, which manages synergistic,
antagonistic, and additive effects between them
This inter-pathway communication is called hormone crosstalk
Hormone crosstalk is essential for tailoring plant responses to diverse microbes and insects in diverse
environments.
Crosstalk between nutrient signalling pathways and immune responses has been observed in rice.
5. Application Strategies for Beneficial Microbes
Beneficial microbes, such as bacteria and fungi, can be applied as biocontrol agents to suppress plant
pathogens
Examples of beneficial microbes used as biocontrol agents include bacteria in the genera
Pseudomonas, Bacillus and Rhizobiacae fungi like Trichoderma and Piriforma.
Microbial consortia can create a stable rhizosphere environment that offers more effective control
against pathogens
The combination of different microorganisms can provide a broader spectrum of disease suppression
and enhance plant protection
