Vam Fungi

Vam Fungi

	Vam Fungi Vesicular-arbuscular mycorrhiza (VAM) fungi shown in are geographically ubiquitous. They are commonly found in association with agricultural crops, shrubs, tropical tree species and some temperate trees. Their nutritional requirements are not specific. VAM associations are formed by non septate Zygomycetes and Phycomycetes .fungi. Some examples are Glomus, Gigaspora, Acaulospora, Entrophospora and Scutellospora of which Glomus is the most common fungus.
The fungi are obligate biotrophs and do not grow on synthetic media and hence are classified according to the morphological characteristics of the spores formed in the soil. VAM fungi produce large resting spores (0.2 mm). The spores can survive adverse conditions. The germ tube dies if it is unable to encounter and successfully penetrate the host root. The fungal hyphae traverses and ramifies in the root cortex. Branches from the intercellular hyphae enter cortical cells where further branching results in highly branched hyphal structures called arbuscles.
They are short-lived and serve as the nutrient transfer mechanism between the fungus and the host. Phosphate transfer possibly occurs across living membranes of the host and the fungus via arbuscles. When the association is well established, hyphal swellings called vesicles form on the mycelium inside and outside the root. The vesicles are sac-like terminal swellings at the tip of hyphae and contain many lipid droplets and function as storage organs. External mycelium form very thick-walled chlamydospores.
These fungi are disseminated both actively and passively. Active dissemination is form one root to another by mycelial growth through soil and passive dissemination is through biotic agents like rodents, worms, insects and birds or abiotic agents like wind and water. VAM fungi interact with other soil microbes like the free-living and symbiotic nitrogen fixers and phosphate solubilisers to improve their efficiency for the biochemical cycling of elements to the host plants.
	(a) Non-mycorrhizal conifer root (b) Mycorrhizal conifer root Forked short roots the diagram show forked short roots caused by an ectomycorrhizal fungus

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