MYCORRHIZA
Mycorrhiza is a symbiotic association between a fungus
and the root of a plant. Mycorrhizal roots often show
wooly covering of fungal hyphae on the surface and
remain in the upper layers of the soil where organic
matter is abundant. A fungus can form association with
roots of many plants and the roots of a plant in turn can
form association with many fungi.
Mycorrhizae are of the following two types
1. Ectomycorrhizae
In this type, the bulk of the fungus grows over the surface
as a mantle. The only part of it lives in the intercellular
spaces of the cortex of the root.
2. Endomycorrhizae
In this type, the fungus grows inside the cortex of the
root with some intercellular hyphae tips. In some forms
of endomycorrhizae, the fungal hyphae develop some
special organs called vesicles with the root cortical cells
This kind of mycorrhizae are called Vesicular Arbuscular
Mycorrhizae (VAM).
The VAM occur in large number of crop plants.
Vesicles
and arbuscules help in absorption of nourishment
form
cortical cells. A single endomycorrhizal fungus can
association with the roots of a number of plants.
Importance of Mycorrhizal Association
(i) Mycorrhiza help in absorption of minerals from
the soil and provide to the root.
(ii) These help in increased absorption of water.
(iii) These produce growth inducing hormones. In the
absence of fungus, Pinus and Betula show growth
despite of providing all types of nutrients.
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(iv) Mycorrhiza enable the plants to grow in mine
deficient soil, saline soil and unfavourable pH and
temperature.
(v) In case of orchids, the fungus absorbs nourishment
from outside and deliver to the germinating seed as
the same is devoid of stored food.
(vi) Mycorrhiza have antimicrobial substances which
protect the root from parasitic fungi and harmful
bacteria by secreting antimicrobial substances.