Improving soil and plant health: the role of biology

Although it may appear to be revolutionary, the concept of using plant growth-promoting rhizobacteria, or PGPR, has been with us for over 30 years. In the rhizosphere, the space immediately surrounding the roots of a plant, a complex series of interactions between the plant, microorganisms and the soil is in place. This unique environment supports a microflora that includes both beneficial and pathogenic microorganisms and exerts a significant influence on the growth and productivity of plants.

Among the many microorganisms in the rhizosphere, PGPR are a group of saprophytic bacteria (meaning that they are harmless, unlike bacteria classified as parasitic) that colonize the rhizosphere—hence the name “rhizobacteria”— and promote plant health and growth. In the soil, rhizobacteria are more numerous in the immediate vicinity of roots due to the metabolites that roots secrete, which serve as nutrients for the bacteria. Over the course of evolution, it would seem that plants and PGPR have developed a close relationship that serves their mutual interests. In addition to being able to feed off root exudates, PGPR also need to affix themselves onto roots in order to be beneficial to plants.

Benefits of PGPR:

The range of known benefits provided by PGPR has grown in recent years. We now know that PGPR benefit plants in several ways:

• Competitive colonization: PGPR can colonize root surfaces, thereby preventing pathogenic microorganisms from infecting a plant. In so doing, PGPR imitate the bacteria that live in our intestines and play a protective role by occupying the space and reducing the quantity of nutrients (food) available to potential pathogens.
• Increased bioavailability of certain essential elements: for instance, some PGPR produce siderophores that allow for iron chelation so that it can then be absorbed by the plant, or a phytase enzyme that allows phosphates to be solubilized.
• Fixation of atmospheric nitrogen: certain PGPR, other than rhizobia in leguminous plants, are able to fix atmospheric nitrogen and transform it into organic nitrogen, which plants can then use.
• Production of phytohormones: auxin and gibberellin hormones are produced by certain PGPR and directly stimulate plant growth.
• Stress reduction: some PGPR produce the enzyme ACC deaminase, which facilitates plant development by reducing their production of ethylene. In this way, PGPR that produce this enzyme can alleviate several plant stresses caused by infections, the absorption of heavy metals, high salinity and even drought.
• Antagonism via the production of antimicrobial molecules: many PGPR produce one or more molecules that fight off various bacteria and fungi. Some of these molecules are genuine antibiotics and play an important role in defending the plant against phytopathogens.
• Induction of immunity: recently, numerous scientific studies have demonstrated that some PGPR are able to stimulate plants’ immune systems, making them more resistant to certain viruses, fungi and even pathogenic bacteria. This characteristic is called ISR (induced systemic resistance).

All these properties make PGPR an attractive option for organic operations and an environmentally friendly alternative in conventional operations to reduce disease pressure and lower the chance of resistance development to commonly used pesticides.

Agriflora SOIL and Agriflora FOLIAR are CFIA-registered supplements that consist of a mix (consortium) of PGPR Bacillus cultures recommend on all crops. Agriflora can be applied onto the seed, onto the dry fertilizer blend, in furrow at planting or sprayed onto the foliage during the growth season. The products help to improve growth and yield, and to protect the crops during periods of stress. They are compatible with conventional treatments in rotation, and represent a promising new tool in preserving yield and quality while protecting the environment.

How Can we help at OMEX?

OMEX offers a full range of Primers to coat the seed; Starters to strategically place phosphorus in-furrow with the seed and Foliars tank-mixable with your pesticide sprays. We also offer water conditioners, plant growth regulators, biologicals and many individual micronutrients able to correct deficiencies when they occur in the field or prevent them before they occur. Talk to your local Ag Retailer or get in touch with your OMEX representative to learn more about OMEX products and how they can help you grow good and healthy crops with a full yield potential.