Vesicular-Arbuscular Mycorrhizas(VAM)
VAM are the common type of mycorrhizas and are found mainly in Bryophytes, Pteridophytes, Gymnosperms and virtually in all families of Angiosperms.
The name vesicular arbuscular derives from structures formed by the infecting fungus in host tissue. Fungus hyphae invade the cell but do not break the host plasma membrane. Inside the cell they branch repeatedly forming dichotomously branched projections called an arbuscle. Vesicles are terminal or sometimes intercalary swellings which may either be between host cells or within them. Vesicle have been ascribed a storage and reproductive function. Within the plant, the mycelium develops only in primary cortex and epithelium of the root and does not penetrate the endodermis into the conducting tissues within the stele. Hyphae within the root are connected to an external soil mycelium. The infection does not alter the morphology if the root or its external appearance and root hairs may be formed.
The group of fungi forming VAMs belong to a single family, the Endonaceae of Zygomycotina.
Significance of VAM fungi
- VAM fungi increase the surface area of the plant root which increases the uptake of nutrient during water absorption.
- VAM plants have larger rootlet size than the normal plant.
- Due to the increased surface area of plant by the presence of VAM fungi, increases the absorption of water in the plant and some times alter the physiology increasing stomatal resistance, resulting in less water loss.
- Fungi are more tolerant to acidity, elemental toxicity and high soil temperature it helps host plant to sustain all respective harsh conditions.
- VAM fungi promote plant survival during seedling phase of growth.
- VAM fungi help to defend roots against soil borne diseases.
- VAM fungi promote beneficial bacteria that may be directly responsible for protection against root pathogens.
- VAM fungi induce generalized host defense mechanism during pathogen attack.