Question

Give a brief account on VAM:
A. Forms fungal sheath around root
B. Fungal hyphae grows intracellularly
C. Fungal hyphae destroys cortical cells to rach phloem of plant
D. Forms hartig net in intercellular spaces of cortex.

Answer 1

Mycorrhiza is the symbiotic association of fungi with the higher plants in which plants provide food and shelter to the fungi and fungi helps in absorption of nutrients from soil. Similarly VAM is a type of fungal association. VAM refers to vesicular arbuscular mycorrhizae.

Complete answer:
Vesicular arbuscular mycorrhiza is formed by the symbiotic relationship between phycomycetes fungi and angiosperm roots. This fungus colonizes the root cortex and introduces its mycelial network into roots and forms vesicles and arbuscules (finger like hyphae) in it. These vesicles are used for storage of food. The arbuscules are their characteristic feature and are actively observed in the function of absorption.
These mycelia may be septate or aseptate which invade the intercellular spaces, thus causing little damage to cells. The VAM are generally identified by the presence of their spores and sporocarps that are found surrounding the roots. Also, VAM inhabits a wide range of host organisms belonging to groups of angiosperms.
Some advantages of VAM are:

Absorption of water, minerals and other nutrients from soil.
Are used as biofertilizers.
Protects the plants from pathogens and infections.
Does not interfere in the ecological balance and is environmentally friendly.

Therefore, the correct answer is option A- forms fungal sheath around roots.

Note: Mycorrhizas are present in 92% of plant families studied with arbuscular mycorrhizae being the ancestral and predominant form, and the most prevalent symbiotic association found in the plant kingdom.