Understanding mycorrhizae and root zone microbes

As interest in biological inoculants continues to grow, we spoke with Dr. Racsko about the advantages of mycorrhizal fungi and beneficial microbes in the soil/media ecosystem and in plant development.

Greenhouse Management: Can you give a technical overview of mycorrhizal fungi and their role in root zone ecosystems?

Jozsef Racsko: Mycorrhizae are beneficial microorganisms that live in partnership with plants. The word “mycorrhizae” actually describes a mutually beneficial, collaborative relationship between the plant and the beneficial fungi. The main role of mycorrhizal fungi is to increase the nutrient and water uptake of the plants’ roots from the soil or other media. They do this by transporting nutrients and water directly into the roots through exchange methods and structures that have evolved over hundreds of millions of years. In exchange for this service to the plant, the mycorrhizae receive carbon, which is delivered by the plant.

GM: How do mycorrhizal fungi help plant development?

JR: Plants’ roots alone are limited to acquiring the nutrients and water needed to develop from a small volume of soil, directly contacting the plant’s root structures. What mycorrhizae do is grow out beyond this depletion zone, beyond this limited soil volume, and extract the nutrients and the water from a larger soil volume. They also produce enzymes that convert non-soluble nutrients into bio-available forms or soluble forms, and increase the production of solubilizing enzymes by the plants. They also work together with other soil microorganisms, which help the fungus extract more nutrients for the plant.

GM: What application practices do you recommend for maximum return on investment?

JR: MycoApply can be applied by sprinkling the granular inoculum in the seeding hole, incorporating mycorrhizae into growing media, or by dipping plugs or bare root cuttings into a solution. MycoApply can also be applied via soil drench, irrigation, boom spray or as a seed treatment. And, since mycorrhizal spores — or colonized root fragments — are very tiny (50 to 300 microns), it’s very important to have a good mix or blend to provide a uniform distribution when applying the inoculum in the growing media. The most important thing that must be emphasized is the need to provide direct contact between the plant roots and the inoculum. With whatever application methods used, the key is to apply it as close to the roots as possible, because although the inoculum by itself is viable, it doesn’t function until in direct contact with growing or emerging roots.

GM: Why is it important for growers to understand the relationship between microbes and management practices?

JR: It’s very important because some management practices can impact the viability or the efficacy of the soil microbes — not just mycorrhizae, but other soil bacteria that are applied. For example, if a grower fumigates the soil or growing medium, this actually kills all the soil microbes (both the bad and the beneficial organisms). After fumigation, growers must replenish the beneficial microbes in the soil through the use of an inoculum product. (The same is true of manufactured growing media used in greenhouses, etc.) Also, if very high levels of nutrients like nitrogen or phosphorous are applied along with the inoculant, it could negatively impact the activity and viability of these microbes. And, since mycorrhizal fungi is a fungus, some of the fungicides commercially available can negatively affect their viability or their efficacy. It is important to know how biological products work in order to maximize your return on investment in the products. The support that can be provided by Mycorrhizal Applications and the distributors of MycoApply is one of the things that sets our company apart. We have been in the business of root-zone microbes since 1995, and are experts in the field of mycorrhizae, so our team and our resources can help ensure proper utilization of these products and help to maximize grower success.