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Mycorrhizal Fungi and Their Importance to Agriculture

Introduction

A mycorrhiza mycorrhizae or mycorrhizas is a symbiotic (generally mutualistic) association between a fungus and the roots of a vascular plant. In a mycorrhizal association, the fungus colonizes the host plant’s roots, either intracellularly as in arbuscular mycorrhizal fungi (AMF), or extracellularly as in ectomycorrhizal fungi. They are an important component of soil fertility.

These are the fungi that form a symbiotic relationship with a plant forming a sheath around the root tip of the plant. The fungus then forms a Hartig Net which means that there is an inward growth of hyphae (fungal cell growth form) which penetrates the plant root structure.

The fungus gains carbon and other essential organic substances from the tree and in return helps the trees take up water, mineral salts and metabolites. Indeed, most forest trees are highly dependent on their fungal partners and in areas of poor soil, could possibly not even exist without them.

Types of Mycorrhizal fungi

Mainly two types;

  1. Ectomycorrhizas :- Hyphae of ectomycorrhizal fungi do not penetrate individual cells within the root
  2. Endomycorrhizas :- Hyphae of endomycorrhizal fungi penetrate the cell wall and invaginate the cell membrane

 

Ectomycorrhizas

Hyphae of ectomycorrhizal fungi do not penetrate individual cells within the root. Ectomycorrhizas consist of a hyphal sheath, or mantle, covering the root tip and a hartig net of hyphae surrounding the plant cells within the root cortex. In some cases the hyphae may also penetrate the plant cells, in which case the mycorrhiza is called an ectendomycorrhiza. Outside the root, the fungal mycelium forms an extensive network within the soil and leaf litter. Nutrients can be shown to move between different plants through the fungal network.

 

Funguses belong to the Basidiomycota, Ascomycota, and Zygomycota. Some Ectomycorrhizas fungi, such as many Leccinum and Suillus, are symbiotic with only one particular genus of plant, while other fungi, such as the Amanita, are generalists that form mycorrhizas with many different plants.

The fungal hyphae are extracellular between the cells of the epidermis and the root cortex. The fungal hyphae form a so-called hartig net and a fungal mantle covering the root tip. Outside the root, the fungal mycelium forms an extensive network within the soil and leaf litter. Nutrients move between different plants through the fungal network

 

Endomycorrhizas

Hyphae of endomycorrhizal fungi penetrate the cell wall and invaginate the cell membrane. Hyphae enter into the plant cells, producing structures that are either balloon-like (vesicles) or dichotomously-branching invaginations (arbuscules).

The structure of the arbuscules greatly increases the contact surface area between the hypha and the cell cytoplasm to facilitate the transfer of nutrients between them.

Arbuscular mycorrhizas are formed only by fungi in the division Glomeromycota. Fossil evidence and DNA sequence analysis suggest that this mutualism appeared 400-460 million years ago, when the first plants were colonizing land.

Arbuscular mycorrhizas are found in 85% of all plant families, and occur in many crop species. The hyphae of arbuscular mycorrhizal fungi produce the glycoprotein glomalin, which may be one of the major stores of carbon in the soil. Arbuscular mycorrhizal fungi have (possibly) been asexual for many millions of years.

Endomycorrhizas are variable and have been further classified as arbuscular, ericoid, arbutoid, monotropoid, and orchid mycorrhizas.
myco-cell-wall

 

 

Comparison between Ectomycorrhizas and Endomycorrhizas (Arbuscular)

myco-root

 

 

What are effects of Mycorrhizal Symbiosis on plant-soil system?

1/ Increased efficacy of nutrient acquisition, plant growth, flower formation and crop yield.
2/ Enhanced resistance to drought, environmental stress and some microbes.
3/ Reduced plant mortality after transplantation.
4/ Improved plant fitness in stressed environment.
5/ Positive effects on soil aggregation and stability and soil water retention
 

What are Advantages of Introducing Mycorrhiza?

1/ A single treatment lasts for the whole plant’s life.
2/ Reduces fertiliser use, watering costs and plantation management costs.
3/ It is compatible with commonly used herbicides and insecticides.
4/ Mycorrhizal plants exploit sources of nutrients in soils at maximum making it a sustainable approach of cultivation and production systems when using a minimum of agrochemicals.
 

What is a commercial value of established Mycorrhiza?

1/ Mycorrhizas are natural for healthy plants and are rare in disturbed, desertified and stressed environments. Thus, artificial inoculation with mycorrhizal fungi brings mycorrhiza to new planted plants and trees in such environments to help them in their establishment, growth and survival rate.
2/ A plant or tree with mycorrhiza has higher capability to survive long-term.
3/ This is a plant health insurance – one-time treatment that will grow with the plant.
 

What is erosion control mediated by functional mycorrhiza?

•  Mycelium of mycorrhizal fungi causes soil aggregation and stabilization

Reasons for reducing Mycorrhizal fungi 

•  Mycorrhizal fungi are found in undisturbed soils with other beneficial soil organisms.
•  Today’s common practices such as tillage, site preparation, road and home construction, mining and removal of topsoil can degrade the mycorrhizal forming potential of soil. The fungi improve the ability of plants to utilize the soil resources by ten to hundreds of times

 

What can we do to replenish Mycorrhizal Fungi?

Mycorrihiza is ideal for any landscape planting situation, establishment of grass seed or sod and will enhance all soil aerification practices. An extensive amount of Mycorrhizae fungi will help to promote extensive root growth, reduce heat and drought stress, improves water and nutrient uptake and can eliminate transplant shock.

The word “mycorrhizae” literally means “fungus-roots” and defines the close mutually beneficial relationship between specialized soil fungi (mycorrhizal fungi) and plant roots. About 95% of the world’s land plants form the mycorrhizal relationship in their native habitats. It is estimated that mycorrhizal fungi filaments explore hundreds to thousands more soil volume compare to roots alone.

 

Mycorrhizal Products

Benefits

•  Improves soil and plant ecosystem
•  Increases plant growth and establishment
•  Reduces transplanting stress and plant loss
•  Increases nutrient and water uptake
•  Improves soil structure and porosity
•  Reduces fertilisers

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