Mutually Benefical

“Myco” – “rhiza” literally means “fungus” – “root” and describes the mutually beneficial relationship between the plant and root fungus.

Mycorrhizal fungi colonize plant roots, expand into the surrounding soil and greatly increase the root’s ability to absorb water and nutrients, while improving plant yields and overall plant performance.

We spoke with Hugh A. Poole, a horticultural technical consultant for Mycorrhizal Applications, an Oregon-based company that develops and manufactures mycorrhizal products for horticulture, agriculture, turf and landscaping, about how growers can use the microbial relationship between fungi and plants to their advantage.

1 | What are mycorrhizal fungi?

Mycorrhizal fungi are beneficial symbiotic soil organisms. They’ve been around for 400 million years in a symbiotic relationship to plants for that entire time. The horticultural industry is just now grasping the whole world of biologicals, not just mycorrhizae but Trichoderma and bacillus and the others have been surviving with plants and combatting disease issues in combination with plants. The endomycorrhizal fungi produced by Mycorrhizal Applications can colonize plants from three main sources of inoculum: spores, colonized root fragments, and vegetative hyphae. Collectively, these forms commercially produced inoculants are called “propagules.” The key is to get these propagules into contact with growing roots, to initiate the symbiotic colonization of the root system.

2 | Why should nursery growers consider mycorrhizal inoculants?

One reason is the industry has become more conscious of water management. Mycorrhizae plays a role in increasing water efficiency. We are concerned about runoff of fertilizer nutrients, especially nitrogen and phosphorus. Mycorrhizae has a role in reducing those, and also reduces the cost that goes with it.

It also helps plants survive stressful conditions. When growers are putting their plants on a shelf at any of the big box stores, plants that have a mycorrhizal relationship will be slower to wilt and will recover from wilt faster than those that do not. When Mycorrhizal plants go into the landscape, the symbiosis is self-perpetuating. These inoculated plants will root and establish faster because of the symbiotic relationship with mycorrhizae.

3 | How do mycorrhizal fungi work with plants?

Mycorrhizae are basically an extension of the root system. If you’ve got a good root system, then you’ve got a healthy plant. Mycorrhizae extends that root system to utilize the entire volume of soil that’s in a container, or if it’s out in a landscape, to utilize a greater percentage of the soil that is in the landscape than the roots could ever possibly reach alone.

The mycelia will absorb water and nutrients, and break down nutrients in a fixed form, like oxides or inorganic matter, and make these nutrients available to the plants.

The nutrients that are most critical in plant production are water, nitrogen, and phosphorus. These three provide about 90 percent of the value to the plant. In exchange for these resources, the plant provides carbohydrates to the fungi. The fungus does not have any chlorophyll so it’s totally dependent on the plant for its food supply. And the plant, because it’s photosynthesizing, has an excess of carbohydrates for the fungi to utilize for its growth.

Endomycorrhizal fungi have a relationship with 80-85 percent of plants species known on earth. Ectomycorrhizal fungi have a relationship with another 10 percent or so. Fortunately for us, many weed species do not have mycorrhizal relationships. So adding mycorrhizae can help support the commercial crops, and help them out-compete the weeds for soil resources.

4 | What types of mycorrhizal fungi work best in the nursery?

In professional nurseries and greenhouses, the most commonly used inoculants are MycoApply Endo, which is a granular formulation, and MycoApply Ultrafine Endo, which is a soluble powder. Both of these products contain an optimized consortium of four endomycorrhizal species, for the diverse benefits that each species offers. The granular product is ideal for incorporation into the soil, as the granular consistency blends evenly with growing media and soils. The ultra-fine powder can be suspended in water, but it can also be incorporated into a soil mix. Ultrafine Endo can be put into a water suspension and applied as a drench to the plants, or used as a plug tray dip. It can also be used in a slurry or a dry powder to treat rooted cuttings or plugs in a quick dip, or in a solution to carry it on. Growers just need to make sure there is good contact between the propagules and the actively-growing roots.

If you topdress, be sure to water it in well so you move the spores down into the root zone where you have actively growing roots. For more information, including rates of application or timing on fungicide application, visit Mycorrhizal Applications’ website.

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