Abstract

Modern agriculture has reached a critical turning point. On one hand, the world requires more food production; on the other, soils have become more depleted, water resources more limited, and stresses such as drought, salinity, and heat have intensified. In such circumstances, relying solely on chemical fertilizers and pesticides is no longer a viable answer for the future of agriculture.

The article under review indicates that one of the most important solutions for the future is the use of Plant Growth-Promoting Rhizobacteria (PGPR). These bacteria live around the plant roots and enter into an active biological relationship with the plant. They can increase nutrient uptake, strengthen root growth, enhance plant resistance to environmental stresses, and even play a defensive role against diseases. Simply put, PGPR can transform soil from a lifeless substrate into a living, intelligent system that supports plant growth.

The Plant is Not a Solitary Being; It is a Living Ecosystem

In the traditional view, a plant is usually seen as an independent organism; it has roots in the soil, absorbs water and nutrients, and grows through sunlight. However, modern science shows that this image is incomplete. A plant is actually part of a larger biological network that includes bacteria, fungi, and other microorganisms.

This collection is called the Plant Microbiome. When we consider the plant and its associated microbes as a single complete unit, we encounter a concept called the Holobiont. This means the plant and the microbes together form a functional system.

The most important part of this system is located around the roots, in an area called the Rhizosphere. The plant root is not just an absorbing organ, but an active chemical and communication center. Through the secretion of compounds such as sugars, amino acids, organic acids, and secondary metabolites, the plant attracts specific microbes. In return, these microbes help the plant’s growth and health by producing beneficial substances.

This is where PGPR plays a vital role. These bacteria settle near the roots and feed on the compounds secreted by them. In exchange, they provide numerous biological services to the plant. This relationship is not a simple transaction; rather, it is an intelligent evolutionary cooperation that has developed over millions of years.

The fascinating point is this: To a large extent, the plant can determine which types of microbes become active around its roots. This means the root does not just absorb food; it can actively manage the microbial environment surrounding itself.

How PGPR Enhances Plant Growth

Plant Growth-Promoting Rhizobacteria (PGPR) operate through several primary pathways. The first pathway is improving plant nutrition. Many nutrients exist in the soil but are not always available to the plant. For instance, phosphorus may be abundant in the soil but exists in an insoluble form that roots cannot absorb. Some PGPR produce organic acids to convert phosphorus into an absorbable form.

Regarding nitrogen, certain bacteria are capable of fixing atmospheric nitrogen and converting it into a form usable by the plant. This is particularly significant in reducing dependence on nitrogen fertilizers. If overused, nitrogen fertilizers cause water pollution, soil degradation, and increased production costs.

The second pathway is the production or regulation of plant hormones. PGPR can produce compounds such as auxins, gibberellins, and cytokinins. These hormones affect root growth, shoot development, cell division, and better nutrient absorption. For example, auxin promotes the development of lateral roots; the more extensive the root system, the more surface area the plant has to absorb water and nutrients.

One of the most critical mechanisms of PGPR is the production of an enzyme called ACC deaminase. This enzyme controls ethylene levels in the plant. Ethylene increases under stress conditions such as drought, salinity, or physical injury. If ethylene levels rise too high, plant growth decreases. By reducing excess ethylene, PGPR helps the plant continue its growth even under harsh conditions.

The third pathway is strengthening the plant's defense system. Some PGPR can activate Induced Systemic Resistance (ISR). This means the plant is placed in a state of "alert" before a severe pathogen attack occurs. This is similar to vaccinating a plant; the plant does not consume much energy, but its defense system becomes ready for a faster reaction.

Consequently, PGPR is not just a "bio-fertilizer." These bacteria simultaneously hold multiple roles: Growth promoter, nutrient provider, hormonal regulator, anti-stress agent, and plant immune booster.

The Importance of PGPR in Future Agriculture and Commercialization

The significance of PGPR becomes even more apparent when viewed in the context of climate change. In the future, agriculture will face challenges such as frequent droughts, rising temperatures, soil salinity, declining farmland quality, and pressure to reduce chemical inputs. In such circumstances, products that can make plants more resistant to stress will hold high economic and strategic value.

PGPR can play a role in several key areas of future agriculture:

• Increasing crop yield without a drastic increase in fertilizer use.
• Reducing pesticide consumption.
• Enhancing plant resistance in harsh conditions.
• Improving soil quality and contributing to sustainable agriculture.

However, there is a crucial point: transferring PGPR from the lab to the field is not simple. Many bacteria that show good results in laboratory conditions do not perform consistently in the field. This is because soil is a highly complex environment. In the soil, PGPR must compete with indigenous microbes, adapt to temperature and moisture fluctuations, and manage to remain established around the roots.

Therefore, product formulation is of great importance. A successful PGPR product does not depend solely on selecting a good bacterium; it must also have a suitable carrier, high shelf life, simple application methods, and predictable field performance. Carriers can be designed as liquids, powders, granules, seed coatings, or compounds like biochar. The article emphasizes that commercializing PGPR requires a phased path: strain isolation, screening, greenhouse testing, field testing, safety assessment, formulation, legal registration, and market launch.

Commercially, this field is not just a scientific topic; it is part of the growing market for Biostimulants and Sustainable Agriculture. Countries and companies that can produce reliable, stable, and economical biological products will have a competitive advantage in the future of agriculture.

Conclusion

The main message of this article is clear: the future of agriculture is not summarized only in producing better seeds, more fertilizers, or stronger pesticides. The future of agriculture lies in understanding and activating the hidden biological systems that exist in the soil and around the roots.

PGPR shows that soil is not an inanimate raw material, but a living and dynamic network. If this network is managed correctly, it can increase plant growth, reduce the consumption of chemical inputs, and raise crop resilience against climate change.

In fact, PGPR represents a paradigm shift:

• From chemical-centered agriculture to biology-centered agriculture.

• From direct plant feeding to managing the ecosystem around the roots.

• From increasing inputs to optimizing the system.

For this reason, Plant Growth-Promoting Rhizobacteria are considered not just a scientific tool, but one of the main pillars of 21st-century sustainable agriculture.

Glossary

PGPR (Plant Growth-Promoting Rhizobacteria): Beneficial bacteria that live near plant roots and promote better growth, increased nutrient uptake, and enhanced plant resistance.

Auxin: A plant hormone that stimulates the growth and expansion of roots.

Gibberellin: A hormone that promotes vertical plant growth and the enlargement of plant organs.

Cytokinin: A hormone that increases cell division and the growth of shoots and leaves.

ACC Deaminase Enzyme: An enzyme produced by certain bacteria that reduces plant stress.

Ethylene: A plant hormone that increases under stress conditions and can slow down or stop plant growth.

ISR (Induced Systemic Resistance): A type of "activated immunity" in plants that prepares them for defense before a disease attack occurs.

Pathogen: Any disease-causing agent, such as bacteria, fungi, or viruses, that damages the plant.

Biostimulants: Substances or microbes that help plants grow better, become stronger, and tolerate stress more effectively (without being traditional fertilizers or pesticides).

Resource:

Backer R, Rokem JS, Ilangumaran G, Lamont J, Praslickova D, Ricci E, Subramanian S and Smith DL (2018) Plant Growth-Promoting Rhizobacteria: Context, Mechanisms of Action, and Roadmap to Commercialization of Biostimulants for Sustainable Agriculture. Front. Plant Sci. 9:1473. doi: 10.3389/fpls.2018.01473