Mycorrhizae: Definition, Types and Examples (With Simple Diagram)

In this article we will discuss about mycorrhizae definition, types and examples

Table of Contents

What is Mycorrhizae?

Vitadini (1842) was first to recognize the benefits of fungal structures (mycelia) that grow around plant roots.
The term “mycorrhiza” was coined by Albert Bernard Frank in 1885
Mycorrhiza is the symbiotic association of fungi with the roots of higher plants.
In this association both the fungi & higher plants derive benefit form each other.
The host plant provides shelter & food for the fungal symbiont & in turn plant acquire an array of benefits such as better uptake of phosphorus, salinity & drought tolerance, maintenance of water balance & overall increase in plant growth.
About 90% of all land plants are associated with mycorrhiza.
The mycorrhizal association is not available in Cruciferae, Chenopodiaceae and Resedaceae.

Peterson and Farquhar (1994) classified the mycorrhizae into following types. These are :

Ectomycorrhiza is commonly called sheathing mycorrhiza.
In this type of mycorrhiza, the root system is completely surrounded by a distinct mantle or sheath of fungal tissue from which the septate hyphae penetrates the outermost cell layer (epidermis & cortex) of all the seeded plants.
No intracellular penetration into the epidermal or cortical cells occurs.
An extensive network of hyphae called Hartig’s net formed between these cells.
Great majority of vascular plants like ferns, Monocots, Dicots, Pinus, Cedrus etc. are formed from these associations with fungi belonging to basidiomycota, ascomycota.
The presence of ectomycorrhiza also prevents growth in length of roots as a result of which swollen or coralloid roots are formed.
E.g., Amanita, Tricholoma, Boletus, Russula, Lactarius (basidiomycota); Gyromitra esculenta (ascomycota)

In endomycorrhiza, the fungal hyphae penetrates the root epidermis and enter the cortex establishing themselves intracellularly in cortical cells.
The fungal hyphae may be septate or aseptate.
Generally the fungal component present on the root surface externally forming a loose mass of hyphae.
Fungal sheath is absent
Hartig’s net is absent
Types of Endomycorrhiza: Vesicular Arbuscular mycorrhiza, Ericoid Mycorrhiza and Orchidoid Mycorrhiza

A. Vesicular Arbuscular mycorrhiza (VAM)

VAM are considered as the most common type of endomycorrhiza.
These are produced by aseptate mycelia fungi which penetrates the root & forming vesicles & arbuscles in plant roots
These are usually found in bryophytes, pteridophytes, gymnosperms (except Pinaceae) & all angiosperms
The fungal hyphae produces very thick walled brown to black balloon like Chlamydospores.
This fungal component is usually from endogonaceae (Zygomycetes)
E,g., Glomus, Gyrospora, Acaulospora etc.

B. Ericoid Mycorrhiza

Ericoid mycorrhizae are found in the different members of Ericaceae like Erica, Calluna, Vaccinum, Rhododendron etc.
The fungi are slow-growing, septate and culturable.
During this association the rootlets of the plants are covered by very sparse, loose, dark, septate hyphae that penetrate the cortex forming intercellular coils.
The fungus gets the photosynthate from the host and improves the mineral uptake and nutrition of the host, especially P and N.
E.g., Pezizella ericae (Ascomycotina) and Clavaria vermiculata (Basidiomycotina)

C. Orchidoid Mycorrhiza

Orchids produce millions of tiny seeds per capsule, there is virtually no storage of food.
Majority of seeds are unable to germinate without exogenous supply of carbohydrates.
Therefore, mycorrhizal association is obligatory for the seeds to germinate.
The Septate hyphae enters the embryo and colonises, develops into coils often called peltrons and it’s provides the nutrition to the seed.
E.g., Rhizoctonia, Corticium, Ceratobasidium etc

These mycorrhizae intermediate in form between ecto and endomycorrhizae types, called ectendomycorrhizae.
Arbustus and Arctostaphylos of Ericaceae show this type of mycorrhizal association.
Fungal sheath present.
Septate hyphae penetrate the outer cortical cells & coils inside it.
Hartig’s net is present in the intercellular spaces
E.g., Wilcoxina, Sphaerosporella

Monotropa hypopitys is a non-green saprophytic herb.
It has short fleshy roots that are invested with a hyphal sheath and often forming Hartig net in the cortical zone.
Due to absence of chlorophyll, they are unable to synthesise and supply carbohydrate to the fungus.
This fungus acts as a bridge between Monotropa and Pine plants.
E.g., Boletus

The mycorrhizal association helps in the formation of dichotomous branching and profuse root growth, thus enhances plant growth.
Mycorrhiza helps in uptake of mineral ions, nutrients and also acts as reservoir.
In nutrient deficient soil, the mycelial association helps in the absorption of N, Ca, P, Zn, Fe, Na and others.
Mycorrhizal association is obligatory for the germination of orchid seeds.
Inoculation of VAM as biofertiliser provides a distinct possibility for the uptake of P in phosphorus-deficient soil.