What Are Deuteromycetes? Key Facts for Biology Students
Commonly called molds, Deuteromycetes are "second-class" fungi carrying no sexual state in their life cycle, reproduced only by producing spores via mitosis. This state of asexual fungi is called Anamorph. In other words, this imperfect fungi class falls under artificial fungi, of which there are approximately fifteen thousand species because of the asexual reproductive mechanism.
Deuteromycetes are also known as Deuteromycota, Deuteromycotina, fungi imperfecti, and mitosporic fungi.
Reproduction in Deuteromycetes
The reproduction phase in Deuteromycetes takes place in different forms. Spores or Conidia is one such form produced directly on the mycelium or on the structure of specialized mycelial cells called Conidiophores. Some forms of these Deuteromycetes don't produce spores. Moreover, non-sporulating fungi are able to propagate themselves by fragmenting the hyphae or by producing a mass of hyphae called a sclerotium. Sclerotia can be microscopic in size or as large as several millimetres in diameter.
Characteristics of Deuteromycetes
Deuteromycetes fungi carry some salient features that make them worth studying.
Deuteromycetes occur as saprophytes on a wide range of substrates, but a large number of these fungi are parasites on plants and animals. This causes a variety of diseases. Leaf- spots, blights, blotch, wilts, rots, anthracnose, etc. are the important diseases of plants, while diseases like meningitis, candidiasis, skin diseases, nail diseases, and others are caused in animals.
The mycelium is made up of profusely branched and septate hyphae posing multinucleate cells and simple pore septa.
The hyphae may be intracellular and their cell wall chiefly contains chitin-glucan.
Deuteromycetes reproduce only asexually. This method of asexual reproduction takes place by hyphal fragments, budding, arthrospores (flat-ended asexual spores formed by the breaking up of cells from the hypha), chlamydospores (thick-walled modified cells functioning as resting spores), and others.
The cell of conidiophores producing conidia is called a conidiogenous cell and is produced either at the tip or the side of the conidiogenous cell, either single or in chains.
The conidiophores are either free or aggregated to form specialized structures like Synnemata and Sporodochia. When they are large, the conidiophores are formed in specialized fruiting layers which are present within the specialized fruiting bodies called Conidiomata.
There is a low sexual reproduction, but the parasexual cycle generally operates in their life to fulfil sexual requirements.
Deuteromycetes Fungi as Pathogens
There are thousands of Deuteromycetes species that are pathogenic to plants and plant parts. Many of these are responsible for the degradation of foods which include fruits and vegetables. All Deuteromycetes, like other types of fungi, are Heterotrophic and need to attach to an organic substrate. All major food products are the best substrates for fungi because, within a short period of time, the fungi will consume and destroy these fruits.
There are some fungi that are eligible to produce toxic chemicals harmful to those who like to eat rotting food. One such chemical is the aflatoxin, produced by the fungus Aspergillus flavus, and is majorly found on peanuts.
Deuteromycetes Classification
The Deuteromycetes is an artificial grouping in which the phylogenetic relationships among taxa are mostly unknown or not apparent. This classification comes under the mitotic states of meiotic groups such as basidiomycetes and especially the Ascomycetes. A small number of taxa has been correlated with meiotic states but the majority hasn't.
There are different formal and informal names used in the past for groups of mitotic fungi. The most common are Deuteromycotina, Deuteromycetes, Fungi Imperfecti, asexual fungi, conidial fungi, and anamorphic fungi.
The Deuteromycetes classification is characterized by the absence of teleomorphic (meiotic) states. It is heterogeneous, i.e., polyphyletic. Reproduction occurs commonly by spores (conidia) produced mitotically (asexually) from conidiogenous cells.
FAQs on Deuteromycetes: Characteristics, Reproduction & Significance
1. What are Deuteromycetes as per the CBSE Class 11 syllabus?
Deuteromycetes, also known as 'imperfect fungi', represent a group of fungi in which only the asexual or vegetative phases are known. Because their sexual reproduction stage (teleomorph) has not been observed or identified, they are placed in this artificial class. Their mycelium is typically septate and branched. They reproduce asexually through spores called conidia.
2. Why are Deuteromycetes commonly called 'imperfect fungi'?
The term 'imperfect' does not imply any biological flaw. Instead, it refers to the fact that our understanding of their life cycle is incomplete. In mycology, the sexual stage of a fungus is referred to as the 'perfect' or teleomorphic stage. Since members of Deuteromycetes are only known to reproduce asexually, lacking an observed sexual stage, they are traditionally called fungi imperfecti or imperfect fungi.
3. What are the key characteristics of fungi belonging to Deuteromycetes?
The main identifying features of Deuteromycetes are:
Reproduction: They reproduce exclusively by asexual means, primarily through the formation of spores called conidia, which are produced on specialised structures called conidiophores.
Mycelium: The fungal body consists of a well-developed, branched, and septate mycelium.
Mode of Nutrition: Most are saprophytes, which act as decomposers of organic litter, while others are parasites that cause diseases in plants and animals.
Classification: It is an artificial class, and fungi are moved out of this group once their sexual stages are discovered.
4. What are some common examples of Deuteromycetes?
Some of the most common examples of Deuteromycetes that are important for the CBSE syllabus include:
Alternaria: A common plant pathogen that causes early blight disease in potatoes and tomatoes.
Colletotrichum: Responsible for causing the 'red rot' disease in sugarcane.
Trichoderma: A beneficial fungus often used as a biocontrol agent to protect plants from other harmful fungi.
5. What is the economic importance of Deuteromycetes?
Deuteromycetes have significant economic importance, both beneficial and harmful.
Beneficial roles: Many species are crucial decomposers, helping in mineral cycling. Some, like Penicillium (historically classified here), are sources of antibiotics. Trichoderma is used in agriculture as a biocontrol agent.
Harmful roles: Many species are pathogenic to plants, causing significant crop losses (e.g., Alternaria, Colletotrichum). Some can also cause diseases in humans, such as ringworm and athlete's foot.
6. How do Deuteromycetes reproduce without a sexual stage?
Deuteromycetes reproduce asexually through the production of spores known as conidia. These spores are exogenous, meaning they are formed externally on the tips of specialised hyphae called conidiophores. When these conidia are dispersed and land on a suitable substrate, they germinate to form a new mycelium. Some species may also reproduce through budding or fragmentation of their hyphae.
7. Why is the classification of Deuteromycetes considered artificial and not a true phylogenetic group?
The classification of Deuteromycetes is considered artificial because it is not based on phylogeny (evolutionary relationships). Instead, it's a 'form-class' or a convenient 'dumping ground' for any fungus whose sexual stage has not been observed. As a result, this group contains fungi that are not closely related. With the advent of molecular techniques like DNA sequencing, many of these fungi are now being properly placed into other classes like Ascomycetes and Basidiomycetes based on their true evolutionary lineage.
8. What happens when the sexual stage of a fungus from Deuteromycetes is discovered?
When the sexual (perfect) stage of a fungus previously in Deuteromycetes is discovered, it is immediately reclassified and moved to its correct class. Most often, these fungi are found to have sexual stages that are characteristic of either Ascomycetes or Basidiomycetes. Once reclassified, the fungus is given a new name based on its sexual form (teleomorph), and its original name (anamorph) is discontinued for formal classification purposes, as per the modern 'one fungus, one name' system.
9. How do Deuteromycetes contribute to nutrient cycling in an ecosystem?
Many Deuteromycetes are saprophytes, playing a vital role as decomposers. They secrete powerful enzymes that break down complex organic materials like dead leaves, wood, and other organic debris. This process of decomposition releases simple inorganic nutrients (like carbon, nitrogen, and phosphorus) back into the soil. This process, known as mineralisation, makes these essential nutrients available for plants to absorb, thereby ensuring the continuous flow of nutrients within the ecosystem.
