Mycorrhiza

1.0What is Mycorrhiza?

The term comes from the Greek words mykes (fungus) and rhiza (root).  A mycorrhiza is the symbiosis between a fungus and a root system. 

A net of fungal filaments envelops the developing root or directly gets in touch with the cells of the root. Hyphae possess a relatively wide surface that makes them possible to absorb water and mineral ions from an essentially greater quantity of soil than the root. The fungus provides water and minerals for the roots, and mycorrhizae are provided by sugars and N-containing components of the roots.

Some plants require the association of mycorrhizae. For instance, mycorrhizae are needed for germination and establishment of Pinus seeds.

In return for their host plants, when two organisms enter into a mycorrhizal relationship, the fungus colonises the host plant's root tissues either intracellularly like in arbuscular mycorrhizal fungi (AMF or AM), or extracellularly like in ectomycorrhizal fungi. Mycorrhizae may associate parasitically with host plants depending on the species or the environment. This association is often mutualistic.

2.0Types of Mycorrhizae

There are two broad types of mycorrhizae:

1. Endomycorrhizae (Arbuscular Mycorrhizae - AM)

• Structure: The fungal hyphae penetrate the root cells and form specialized structures called arbuscules (for nutrient exchange) and vesicles (for storage).
• Hosts: Found in the majority of terrestrial plants, including crops like wheat, rice, and maize.
• Function: Efficiently absorb nutrients like phosphorus, zinc, and copper.
• Improve water uptake. Increase plant resilience to environmental stresses.

Arbuscular Mycorrhizal Fungi (AMF)

These fungi form arbuscular mycorrhizae, which are the most common type of mycorrhizae and occur in about 80% of vascular plants.

Examples:

• Glomus species (e.g., Glomus intraradices, Glomus mosseae): Widely used in agriculture and forestry to improve plant growth.
• Rhizophagus irregularis: A well-studied AMF species often used in research and inoculants.

3. Ectomycorrhizae:

• Structure: The fungal hyphae form a sheath or mantle around the outer surface of the root and penetrate the outer cortex cells without penetrating the cell walls. The hyphae extend into the soil to form an extensive network.
• Hosts: These are most commonly associated with woody plants, including pines, oaks, and birches.
• Function: Promote nutrient uptake, particularly phosphorus and nitrogen.
• Protect roots from pathogens. Improve soil structure by stabilizing soil particles.

Ectomycorrhizal Fungi

These fungi form ectomycorrhizae, which are primarily associated with trees in forests, especially in temperate and boreal ecosystems.

• Examples:
• • Boletus edulis: Known as the porcini mushroom; forms ectomycorrhizae with tree species like pines and oaks.
  • Amanita species (e.g., Amanita muscaria): Forms associations with birch, pine, and spruce.
  • Pisolithus tinctorius: Widely used in forestry to promote tree growth.
  • Laccaria bicolor: Commonly associated with conifers and used in forestry research.

3.0Difference Between Ectomycorrhizae and Endomycorrhizae

4.0Uses and Benefits of Mycorrhizae

Increased Nutrient Uptake: Fungal hyphae extend beyond the root zone, reaching nutrients that cannot be accessed by roots alone. The best nutrient uptake is particularly efficient in phosphorus, as this nutrient is immobile in soil.

Increased Water Absorption Hyphal networks improve the access of a plant to water in soil during drought conditions.

Resistance to Diseases- Mycorrhizal fungi form a protective barrier around roots to protect them from soil-borne pathogens.

Stress Resistance- Help plants tolerate stress factors such as salinity, heavy metals, and drought.

Improved Soil Structure: Fungal hyphae exude chemicals such as glomalin, which agglutinates soil particles, improving porosity and aeration.

5.0Advantages to Fungi

Mycorrhizal fungi obtain carbohydrates, which are sugars resulting from photosynthesis, from plants. The plant is supplied with these sugars via its roots, making this a symbiotic relationship.