Mycorrhizae – The fungi that agriculture needs, but why?

Introduction

Over the past few decades, there has been an increasing interest in the identification and cultivation of beneficial soil microorganisms. It is widely documented at this point that many bacteria, fungi, and other microorganisms can help plants in combatting disease, making essential nutrients available and acquiring water in when it’s short in supply. Within this group of beneficial microorganisms exists a group of fungi called mycorrhizae. These fungi can grow in a symbiotic relationship with most plants and have been investigated as growth and quality enhancement tools for agricultural and horticultural crops.

Most mineral soils in North America contain some trace of mycorrhizal fungi, but rarely at levels that would allow for proper colonization. Mycorrhizae are host specific and will only colonize certain plants, so in some soils there won’t be any native mycorrhizae that will benefit these plants. For instance, plants in the brassica family rarely form relationships with mycorrhizae. Most plants would benefit from an addition of mycorrhizae to the soil.

What are mycorrhizae?

The term mycorrhiza (singular) means “fungus root” and describes the symbiotic relationship between fungus and plant root. The relationship between fungus and plant begins when fungal spores germinate and create threadlike structures called hyphae which enter the epidermis or outermost layer of cells of the plant root.

Image: Fungal hyphae interacting with plant root cells

Once the plant root is colonized, the fungus will disperse a vast but dense network of hyphae throughout the soil to greatly increase the absorptive area of the fungus. Once the network of hyphae is extended, plants will generally improve their ability to uptake nutrients and water as the fungus acts as an extended root system for the plant. It’s been observed that mycorrhizal fungi will almost always improve the intake of phosphorus, zinc, manganese and copper into a plant.

Types of Mycorrhizae

The classification of mycorrhizae is based on the inter-relation of fungal hyphae to plant root cells. Ectomycorrhizae form a network of hyphae that do not penetrate the root cells but instead colonize the outer surface of roots. Ectomycorrhizal fungi can reproduce without the presence of a plant host.