Plant growth-promoting rhizobacteria (PGPR) – Definition & Detailed Explanation – Soil & Fertilizers Glossary

I. What are Plant growth-promoting rhizobacteria (PGPR)?

Plant growth-promoting rhizobacteria (PGPR) are a group of beneficial soil bacteria that colonize the roots of plants and promote their growth and health. These bacteria have the ability to enhance plant growth by various mechanisms, such as increasing nutrient availability, producing plant growth hormones, and protecting plants from pathogens. PGPR are commonly found in the rhizosphere, the region of soil surrounding plant roots where they interact with the plant and other soil microorganisms.

II. How do PGPR benefit plants?

PGPR benefit plants in several ways. One of the main benefits is their ability to solubilize nutrients in the soil, such as phosphorus and iron, making them more available to plants. This can help improve plant growth and development, as these nutrients are essential for various physiological processes. Additionally, PGPR can produce plant growth hormones, such as auxins and cytokinins, which can stimulate root and shoot growth.

Furthermore, PGPR can help protect plants from pathogens by competing for resources and space in the rhizosphere, as well as producing antimicrobial compounds that inhibit the growth of harmful microorganisms. This can help reduce the incidence of plant diseases and improve overall plant health.

III. What are the mechanisms of action of PGPR?

PGPR can promote plant growth through various mechanisms. One mechanism is the production of enzymes that can solubilize nutrients in the soil, making them more available to plants. For example, some PGPR produce phosphatases that can break down organic phosphorus compounds into inorganic forms that plants can absorb.

Another mechanism is the production of plant growth hormones, such as auxins and cytokinins, which can stimulate plant growth and development. These hormones can promote root and shoot growth, as well as enhance nutrient uptake and stress tolerance in plants.

Furthermore, PGPR can help protect plants from pathogens by producing antimicrobial compounds that inhibit the growth of harmful microorganisms. They can also compete for resources and space in the rhizosphere, reducing the colonization of pathogens on plant roots.

IV. How can PGPR be applied to soil?

PGPR can be applied to soil through various methods, such as seed inoculation, soil drenching, and foliar spraying. Seed inoculation involves coating seeds with a suspension of PGPR before planting, allowing the bacteria to colonize the roots of the emerging seedlings. Soil drenching involves applying a solution of PGPR directly to the soil around the plant roots, while foliar spraying involves spraying the bacteria onto the leaves of the plants.

In addition, PGPR can also be applied as biofertilizers or biopesticides, which are products containing live beneficial microorganisms that can enhance plant growth and protect plants from pests and diseases. These products can be applied to soil or plants to improve their health and productivity.

V. What are the advantages of using PGPR in agriculture?

There are several advantages to using PGPR in agriculture. One of the main advantages is their ability to enhance plant growth and productivity by improving nutrient uptake, stimulating root and shoot growth, and protecting plants from pathogens. This can lead to increased crop yields and improved crop quality.

Furthermore, PGPR can help reduce the need for chemical fertilizers and pesticides, as they can improve nutrient availability in the soil and protect plants from diseases. This can help reduce the environmental impact of agriculture and promote sustainable farming practices.

Additionally, PGPR can help improve soil health by increasing soil fertility, enhancing soil structure, and promoting beneficial microbial communities. This can lead to improved soil quality and long-term sustainability of agricultural systems.

VI. What are some examples of PGPR strains commonly used in agriculture?

There are several PGPR strains that are commonly used in agriculture to promote plant growth and health. Some examples include:

1. Bacillus subtilis: This bacterium produces antimicrobial compounds that can inhibit the growth of plant pathogens. It also produces enzymes that can solubilize nutrients in the soil, making them more available to plants.

2. Pseudomonas fluorescens: This bacterium can help protect plants from diseases by producing antibiotics and competing for resources with harmful microorganisms. It can also stimulate plant growth by producing plant growth hormones.

3. Azospirillum brasilense: This bacterium can fix atmospheric nitrogen and make it available to plants, reducing the need for nitrogen fertilizers. It can also produce plant growth hormones that can stimulate root growth and enhance nutrient uptake.

Overall, these PGPR strains and others can play a valuable role in promoting plant growth and health in agriculture, leading to increased crop yields, improved soil health, and sustainable farming practices.