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What is Mycelium in Fungi?

IVSAT 2024

Mycelium Definition: Mycelium is a mass of branching, thread-like hyphae that make up the vegetative portion of a fungus or fungus-like bacterial colony. Shiro is a term used to describe a mass of hyphae, especially in fairy ring fungi. Mycelium-based fungal colonies can be found in and on soil and a variety of other substrates.

Mycelium Meaning: 

As we already looked into the definition of mycelium, take a look at the Mycelium meaning here. Fungi's plant bodies are usually made up of branched and filamentous hyphae. Mycelium is a net-like structure formed by Mycelium Hyphae.

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Mycelium Structure

Fungal mycelia look like a cotton ball to the naked eye. A network of hyphae bundles together to form mycelia, which can be found on substrates, in the soil, or underground.

Mycelia, unlike fungal hyphae, are strongly branched, making them transparent to the naked eye. In addition to being strongly branched, they have also been shown to be ishighly septate, meaning that septa divide tubular structures into compartmental cells.

The following are some of the organelles present in these cells:

  • Ribosomes 

  • Nucleus (the cells may be binucleate or multinucleate)

  • Globules

  • Vacuoles

  • Mitochondria

The plasma membrane surrounds each cell, which is in turn surrounded by the cell wall. As the mycelia begin to expand and branch, this strengthens them.

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Modifications of Mycelium Fungi

  • The majority of fungi have basic hyphae.

  • In some advanced fungi, hyphae may change in response to functional requirements.

  • Hyphal modifications are hyphal aggregations that are necessary during the life cycle of fungi to perform specific functions.

  • In fungi, important hyphal modifications include:

1. Prosenchyma:

  • Fungi type prosenchyma, which is made up of loosely packed tissue.

  • When the component hyphae are arranged more or less parallel to one another, prosenchyma is formed, and the entire mass becomes a felt-like structure.

  • The hyphae join together to create a loosely woven frame.

  • The uniqueness of fungal hyphae is preserved in prosenchyma.

  • Plectenchyma or Proso-plectenchyma are other names for Prosenchyma.

2. Pseudo-Parenchyma:

  • In cross-section, the hyphae are tightly entangled and form a tissue-like structure.

  • The hyphae lose their identity and are no longer distinguishable from one another in pseudo-parenchyma.

  • In cross-section, pseudo-parenchyma resembles the parenchymatous tissue of higher plants.

  • Para-plectenchyma is another name for them.

3. Rhizomorphs

  • In certain fungi, rhizomorphs are thick strands or root-like aggregations of somatic hyphae.

  •  Mycelial cords is another name for them.

  • They're gelatinous, dark brown, and have coiled structures that look like rope.

  • The intertwining of hyphae in rhizomorphs is too close, causing hyphae to lose their individuality.

  • Individual hyphae are aligned in a parallel pattern.

  • Individual hyphae have a lower infection potential than Rhizomorphs.

  • They're perennating systems with a lot of penetration power.

  • Rhizomorphs can live for several years and, in the right conditions, can produce new mycelia.

4. Sclerotium

  • In certain fungi, sclerotia is a compact globose structure produced by the aggregation of hyphae.

  • The interwoven hyphae are extremely compact, and the individuality of the hyphae is lost, resulting in rounded, cushion-like structures.

  • Sclerotia will live for a long time, sometimes even years.

  • They are the dormant stage of some fungi.

  • They aid in vegetative reproduction by accumulating food materials.

  • The outer cells of sclerotia turn a dark brown colour, while the inner cells remain colourless.

5. Appressorium

  • Appressorium is a terminal simple or lobed swollen structure of germ tubes on infecting hyphae

  • Appressorium is found on many parasitic fungi such as rusts and powdery mildews

  • It adheres to the surface of the host and helps in the penetration of hyphae

  • The infection peg is originated from the appressorium

6. Haustorium

  • Haustoria are obligate parasites' intracellular absorption structures.

  • They're designed to absorb food particles from the host tissue.

  • Haustoria come in a variety of sizes and shapes.

  • Knob-like, elongated, finger-like, or branched shapes are possible.

  • They secrete enzymes that aid in the hydrolysis of the host's proteins and carbohydrates.

7. Stroma

  • Stroma are somatic structures that are compact.

  • They're pseudoparenchymatous structures that look like flat cushions.

  • They normally have fructifications on or in them.

8. Snares

  • Predaceous fungi create snares, which are trap-like structures that capture small organisms like nematodes and protozoans.

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Mycelium Functions

  • Mycelium plays an important role in the decomposition of various complex organic compounds since they expand and spread widely. Biomass is converted to compost in this way.

  • Because of their symbiotic relationship with plants, they can increase crop yields.

  • They have the potential to ruin food.

  • As the mycelium continues to expand and spread within or on the surface of the substrate, it absorbs nutrients, which are then transferred to the fruiting bodies to promote growth and reproduction.

  • They are also involved in reproduction.

Mycelium Reproduction

When a spore germinates to form homokaryotic mycelia, mycelia are involved in reproduction. The homokaryotic, also known as homokaryon, are mycelia with nuclei of the same genotype.

As spores like basidiospore germinate, they produce homokaryotic mycelium, which is made up of monokaryon or uninucleate cells. The hyphal walls crack open when two monokaryons come into contact, a phenomenon known as hyphal anastomosis. This allows the nuclei of vegetatively compatible monokaryons to pass into the other monokaryon's mycelia.

Finally, the formation of binucleate cells and, as a result, the formation of dikaryon mycelium occurs. The dikaryotic mycelium can produce fruiting bodies that are involved in sexual reproduction depending on external conditions (moisture, temperature, and pH, among others). 

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Difference Between Mycelia and Hyphae

  • Though fungal hypha is increasingly branching to form mycelium, mycelium is made up of hyphal threads, which are the vegetative component of fungi.

  • The mycelia are the fungi's bodies, while the hyphae are the fungi's building blocks.

  • Mycelia are densely branched and thick, while hyphae are not.

  • Some hyphae can be seen with the naked eye, but not all mycelia.

Similarity Between Mycelia and Hyphae

Decomposition of substrates is aided by both hyphae and mycelium.

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FAQs on Mycelium

1. Can Mycelium Survive Cold Temperatures?

Ans. Higher temperatures delay the growth rate and can cause heat damage to the mycelium, so the air temperature should not exceed 27°C. Freezing mushroom mycelium on an agar medium without cryoprotectants can damage or destroy it, so it should be avoided.

2. What Is the Ideal Temperature to Grow Mycelium?

Ans. Temperatures under which mycelium is growing should be held within a certain range. P. cubensis, for example, colonises most quickly at 75-80°F (24-27°C). Temperatures above this range can destroy mycelium and encourage contaminant growth, while temperatures below this range can slow colonisation.

3. What Does Mycelium Feed On?

Ans. Mycelium, like single-celled yeast, takes in small molecules of food—typically sugar, but also wood or plant waste — and secretes enzymes that break these materials down into digestible morsels.

4. What is the Composition of Mycelium?

Ans. Mycelium is a natural polymeric composite fibrous substance made up primarily of natural polymers such as chitin, cellulose, and proteins. 

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