Mycorrhiza
A mycorrhiza is a symbiotic association between a plant and a fungus. The plant makes organic
molecules such as sugars by photosynthesis and supplies them to the fungus, and the fungus
supplies to the plant water and mineral nutrients, such as phosphorus, taken from the soil.
The word mycorrhiza was coined by the German scientist Albert Bernhard Frank in 1885. The
word mycorrhiza is derived from the Greek words –‘mukes’ meaning fungus and ‘rhiza’ meaning
roots.
95% of all the world's plant species form mycorrhizal relationships with fungi and in majority of
cases the plant would not survive without them. Among these 95% of plants 83% are Dicots and
79% are Monocots. About 100% Gymnosperms are mycorrhizal. Brassicaceae, Cyperaceae, and
Juncaceae family do not have mycorrhizal associations.
Mycorrhizae have existed for a very long time and can be demonstrated in the fossilized roots of
some of the earliest land plants.
Some scientists have suggested that plants were only able to move on to land when they had
developed mycorrhizal relationships with fungi.
Classification of mycorrhiza
Ectotropic Mycorrhiza (Ectomycorrhizae)
Endotropic Mycorrhiza (Endomycorrhizae)
Ectomycorrhizae
• Ectomycorrhizas, or EM, are typically formed between the roots of around 10% of plant
families, mostly woody plants including the eucalyptus, oak, pine, deodar and rose
families.
• Commonly associated with trans temperate forest trees.
• Ectomycorrhizal fungi form a sheath or mantle around the root, and hyphae proceed
through the soil increasing the surface area.
• The fungus grows within the root cell wall but never penetrates the cell interior.
• It grows between the cells of the cortex to form Hartig net.
• The Hartig net present outside the endodermis and meristematic zones is the site for
nutrient exchange.
• Colonization of root tips induces marked changes in the host root morphology.
Advantages of ectomycorrhizae
• Extensive multibranching hyphae increases the water holding capacity of plants.
• Increase the tolerance of plants against drought, high soil temperature, organic and
inorganic soil toxins, extremes of soil acidity to sulphur and aluminium.
• Prevent infection of feeder roots by some rot pathogens.
• Enhance the uptake of many nutrients. (P, Cu, Zn through Hartig net)
• Disease control through barrier effect.
• Play a key role in afforestation.
Endotomycorrhizae
Arbuscular mycorrhizae (often called AM) are the most common and widespread of all
mycorrhizae and are found in as many as 85%-90% of the world's plant species. Commonly
associated with agricultural, horticulture crops in addition to tropical trees.
The external hyphal mantle or sheath is absent or scanty. The fungal hyphae enter inside the root
cortex and penetrates the cortical cells.
This is not a destructive parasitic association but endomycorrhiza are present at certain times as a
part of normal root development. AM fungi penetrate the cell walls of root cells. They grow
between the cell wall and cell membrane forming arbuscules. VAM fungi produce vesicles for
lipid storage.
1: Extraradical hyphae 2: Appressorium/hyphopodium 3: Arbusculum; 4: Vesiculum
5: Intercellular hyphae 6: Intracellular hyphae 7: Hyphal coils
Two main types of root colonization in arbuscular mycorrhizae (AM)
• In the Arum-type the fungal hyphae grow intercellularly and well-developed arbuscules
are formed on branches entering the neighboring cells.
• In the Paris-type the hyphae grow intracellularly, develop hyphal coils in some cortical
cells and smaller arbuscules develop on these coils. Both the fungal and the plant partner
influence the type developed
Ectomycorrhizae Endomycorrhizae
Fungi produce majority of its structure outside Generally, fungi produce its typical structures,
the root system vescicles and arbuscules inside the root system.
Commonly associated with temperate forest Commonly associated with agricultural,
tree roots. horticultural and tropical trees.
Form a complete mantle or sheath over the Have a loose network of hyphae in the soil and
surface of the rot and hyphae grows out into an extensive growth within the cortex cells of
the soil. the plants
Can be cultured on artificial media Cannot be cultured on artificial media
Cause morphological changes in roots. Doesn’t cause morphological changes in roots.
