Mutualistic Fungi

Mutualism is the association in which both partners are benefited. The two key mutualistic symbiotic association formed by the Fungi are lichens and mycorrhizae.

A) Lichens:

Lichens are an association between a fungus (mostly Ascomycetes and imperfect fungi and a few basidiomycetes) a cyanobacterium and green alga. The body of a lichen has three layers:

(1) The upper layer is thin and tough which consists of fungal hyphae.
(2) The middle layer consists of fungal hyphae interwoven with photosynthetic cell.
(3) Bottom layer consists of loosely packed fungal hyphaes.
The specialized fungal hyphae which penetrate or envelope the photosynthetic cells, transfer nutrients directly to the rest of the fungus. Three types of lichens are recognized:

1) Crusticose Lichens:

These are compact, often seen on bare rocks or on tree bark.

2) Foliose Lichens:

These are leaf like.

3) Fruticose Lichens:

These are shrub like and branched.

The lichens vary in color, shape, over all appearance, and growth form. Lichens are efficient at acquiring nutrients and moisture. and therefore, they can survive in areas of low moisture and low temperature as well as areas with poor and no soil.

They produce and improve the soil, thus making it suitable for plants to invade the area. Unfortunately, lichens also take up pollutants and cannot survive where air is polluted. Therefore, their presence is a bioindicator that the air is healthy for humans to breathe.

B) Mycorrhizae:

Mycorrhizae are mutualistic relationships between soil fungi and the roots of most plants. This association occurs in 95% of all families of higher plants.

Fungal hyphae increases the amount of soil contact and total surface area for absorption. The hyphae help in the direct absorption of phosphorus, zinc, copper and other nutrients from the soil into the roots.

Plants whose roots are invaded by mycorrhizae grow more successfully than do plants without mycorrhizae.

There are two types of mycorrhizae in which mycelium extends far out into the soil.

1. Endomycorrhizae:

Penetrate only into the cell wall of outer cells of plant root forming coils, swellings and minute branches and also extend out into sorrounding soil.