Mycorrhizae inoculation refers to the symbiotic interaction (physical and chemical) of a fungus with the root structure of vascular plants. These fungi basically act as an extension of the plants’ root system, bringing more water and nutrients from the soil to the root itself. The fungi can add from 100 times up to 1,000 times the surface area of the root, while also breaking down nutrients such as organic nitrogen, phosphorus, and iron to make them more accessible to the plant. In return, the plant gives sucrose and glucose to the fungus.

There are three general categories - ectomycorrhizae, endomycorrhizae, and ericoid mycorrhizae. Ectomycorrhizae are less common, found around about 10 percent of plant families. These fungi form a sheath around the root and the hyphae (long filamentous structures) extend out into the soil. Endomycorrhizae are much more common. Arbuscular mycorrhizae are a subset of endomycorrhizae found around 85 percent of plant families, including crop species. This fungus does not form a sheath around the root, it enters into the plant cells and produces hyphae. Ericoid mycorrhizae are not as well-studied, but they are commonly associated with leguminous and carnivorous plants. Their structure is different from the other two because it stays tightly clustered around the root, as opposed to the extensive branching out seen in ecto- and endomycorrhizae. Plants can have from one to many different species of mycorrhizae fungi living in symbiosis.