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Chapter 8

What are Mycorrhizae ?. Chapter 8. What are Mycorrhizae?. The word mycorrhizae was first used by German researcher A.B. Frank in 1885, and originates from the Greek mycos , meaning 'fungus' and rhiza , meaning 'root'.

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Chapter 8

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  1. What are Mycorrhizae? Chapter 8

  2. What are Mycorrhizae? • The word mycorrhizae was first used by German researcher A.B. Frank in 1885, and originates from the Greek mycos, meaning 'fungus' and rhiza, meaning 'root'. • Mycorrhiza is a symbiotic mutualistic relationship between special soil fungi and fine plant roots; it is neither the fungus nor the root, but rather the structure formed from these two partners.

  3. Since the association is mutualistic, both organisms benefit from the association. • The fungus receives carbohydrates (sugars) and growth factors from the the plant, which in turn receives many benefits, including increased nutrient absorption. • In this association, the fungus takes over the role of the plant's root hairs and acts as an extension of the root system

  4. Mycorrhizas are highly evolved, mutualistic associations between soil fungi and plant roots. It is commonly known as root fungi. • This association are members of the fungus kingdom (Basidiomycetes, Ascomycetes and Zygomycetes) and most vascular plants. • Host plant receives mineral nutrients while the fungus obtains photosynthetically derived carbon compounds from the plant.

  5. Mycorrhizal associations involve 3-way interactions between host plants, mutualistic fungi and soil factors.

  6. Types of Associations • At least 7 different types of mycorrhizal associations have been recognised, involving different groups of fungi and host plants. • Ectendo-, arbutoid- and monotropoid mycorrhizal associations • Orchid mycorrhizas • Ericoid mycorrhizas • ECM and VAM associations will be considered in detail

  7. Ectomycorrhizas (ECM) • The fungus hyphae develop on the root surface. • Majority develop fruiting bodies • Basidiomycetes and other fungi form short swollen lateral roots covered by mantle hyphae • (layers of fungal hyphae covering the root surface.) • ECM associations consist of a soil mycelium system, linking mycorrhizal roots and storage or reproductive structures. • Ectomycorrhizal roots are characterised by the presence of a mantle and Hartig net,

  8. Hartig net

  9. Sclerotia • It is a dark, hard and irregular structure • It is the resting bodies formed from the hyphalaggregation • It is a fungal “survival structure” • Formed under unfavorable conditions

  10. Rhizomorphs • Root-like structures, thicker than mycelium. • A thick strands of hyphae • Extend from the mycelium through the substrate • They help in spreading the fungus from one root system to another root system.

  11. Mycorrhizal roots

  12. Fruiting Bodies

  13. Vesicular-arbuscular mycorrhizas arbuscular mycorrhizas, (VAM or AM) • are associations where Zygomycete fungi in the Glomales produce arbuscules, hyphae and vesicles within roots and outside. • Does not produce fruiting bodies. • Does not form mantle on root surface. • Grow intercellular and intracellular in the root tissue but does not harm the roots

  14. Glomus intraradices

  15. WHY MYCORRHIZAS ARE IMPORTANT • Increased plant nutrient supply by extending the volume of soil accessible to plants. • Increased overall absorption capacity of roots due to morphological and physiological changes in the plant. • There is increased absorption surface area, greater soil area explored (since the fungus acts as an extension of the root) • greater longevity of absorbing roots • better utilization of low-availability nutrients • better retention/storage of soluble nutrients, thus reducing leaching losses.

  16. Increased plant nutrient supply by acquiring nutrient forms that would not normally be available to plants • Increased mobilization and transfer of nutrients (P, N, S, micronutrients Cu, Zn) from the soil to the plant. • Mycorrhizal fungi have been estimated to "substitute" up to 500 lb/a of P for citrus and 170 lb/a for soybeans in tropical areas. • Root colonisationby ECM and VAM fungi can provide protection from parasitic fungi and nematodes through physical and chemical means. • Secretion of antibiotics and support of a community that competes or antagonizes pathogenic microorganisms, thus aiding in disease suppression;

  17. Increased establishment, nodulation and atmospheric nitrogen fixation capacity in legumes. • Increased production of plant growth hormones such as cytokinins and gibberelins; • Modification of soil-plant-water relations, promoting better adaptation of plant to adverse environment conditions. • At elevated heavy metal concentrations in soils, mycorrhizal fungi have been shown to detoxify the environment for plant growth.

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