Ectomycorrhizae

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Mycorrhizae Fungal Symbioses with Roots Ectomycorrhizae Cultural Characteristics of Ectomycorrhizal Fungi Absorption of Nutrients Techniques of Ectomycorrhizal Inoculation Resistance to Plant Diseases by Ectomycorrhiza

Ectomycorrhizae

Ectomycorrhizae
In general, the fungi involved in ectomycorrhizae come under Basidiomycetes from the families, Amanitaceae, Boletaceae, Cortinariaceae, Russulaceae, Tricholomataceae, Rhizopogonaceae and Sclerodermataceae. They are included in the genera-Amanita, Boletus, Cantharellus, Cortinarius, Entoloma, Gomphidius, Hebeloma, Inocybe, Lactarius, Paxillus, Russula, Rhizopogon, Scleroderma and Cenococcum. Many of these fungi show a wide host spectrum.

Different types of mycorrhizae

1. Spore	2. External hypha	3. Intracellular arbuscule	4. Vesicle
5. Intercellular coiled hyphae	6. Mycelial strand	7. Sheath	8. Hartigs net
9. Intercellular net with penetrating hyphae		10. more or less loose sheath

Photograph showing dichotomously branching roots of Pinus

Likewise, one and the same host may be infected by more than one fungus as exemplified by Pinus sylvestris from whose mycorrhizal roots as many as 40 fungal species have been isolated. When the defence reaction of the higher symbiont diminishes as it is likely to happen in senescent or diseased trees, the lower symbiont may become endotrophic. Such instances have been designated as 'ectendotrophic mycorrhizae' or 'ectendomycorrhizae'. A survey of literature on mycorrhizal associations also reveals descriptions known as 'Pseudomycorrhizae' which refer to the thin and long roots which are infected with fungi. The fungi are intracellular in such roots and it is difficult to define whether fungi exist in ectendomycorrhizae as parasites or symbionts. Mention must also be made of the mycorrhiza of Monotropa (which in Greek means living alone), a native of North America growing in forests under Pinus and Quercus.

The plant does not contain chlorophyll and a common mycorrhizal fungus Boletus transports nutrients from the forest trees to Monotropa. An ectomycorrhizal root is devoid of root hairs and is covered by a layer or sheath of fungal hyphae which almost looks like host tissue. This layer is called pseudoparenchymatous sheath. From this sheath, hyphae enter the cortex and remain only in the outer cortical cells to form a network called the 'Hartig net' (named after the German botanist Hartig). Ail the nutrients are absorbed by the fungal mantle and transported to the root through the Hartig net. One of the frequent questions that have been posed is whether such plants can grow in the absence of ectomycorrhizae.

Researches on this subject have shown that if essential nutrients are made available, plants can still grow in the absence of its symbiont. The mycorrhizal habit is, however, indispensable in soils and seedlings in nursery beds deficient in major nutrients, like nitrogen and phosphorus. When trees are introduced to new regions, inoculation of soil with mycorrhizal fungi has been found to be a necessary prerequisite for the establishment of the mycorrhizal habit

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Endomycorrhizae of Orchids Arbuscular Mycorrhiza Isolation of AM Fungal Spores Methods of AM Fungal Inoculation Legume Arbuscular Mycorrhiza Interaction

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