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24.1C: Fungi Reproduction - Biology


Fungi can reproduce asexually by fragmentation, budding, or producing spores, or sexually with homothallic or heterothallic mycelia.

Learning Objectives

  • Describe the mechanisms of sexual and asexual reproduction in fungi

Key Points

  • New colonies of fungi can grow from the fragmentation of hyphae.
  • During budding, a bulge forms on the side of the cell; the bud ultimately detaches after the nucleus divides mitotically.
  • Asexual spores are genetically identical to the parent and may be released either outside or within a special reproductive sac called a sporangium.
  • Adverse environmental conditions often cause sexual reproduction in fungi.
  • Mycelium can either be homothallic or heterothallic when reproducing sexually.
  • Fungal sexual reproduction includes the following three stages: plasmogamy, karyogamy, and gametangia.

Key Terms

  • homothallic: male and female reproductive structures are present in the same plant or fungal mycelium
  • gametangium: an organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants
  • spore: a reproductive particle, usually a single cell, released by a fungus, alga, or plant that may germinate into another
  • sporangium: a case, capsule, or container in which spores are produced by an organism
  • karyogamy: the fusion of two nuclei within a cell
  • plasmogamy: stage of sexual reproduction joining the cytoplasm of two parent mycelia without the fusion of nuclei

Reproduction

Fungi reproduce sexually and/or asexually. Perfect fungi reproduce both sexually and asexually, while imperfect fungi reproduce only asexually (by mitosis).

In both sexual and asexual reproduction, fungi produce spores that disperse from the parent organism by either floating on the wind or hitching a ride on an animal. Fungal spores are smaller and lighter than plant seeds. The giant puffball mushroom bursts open and releases trillions of spores. The huge number of spores released increases the likelihood of landing in an environment that will support growth.

Asexual Reproduction

Fungi reproduce asexually by fragmentation, budding, or producing spores. Fragments of hyphae can grow new colonies. Mycelial fragmentation occurs when a fungal mycelium separates into pieces with each component growing into a separate mycelium. Somatic cells in yeast form buds. During budding (a type of cytokinesis), a bulge forms on the side of the cell, the nucleus divides mitotically, and the bud ultimately detaches itself from the mother cell.

The most common mode of asexual reproduction is through the formation of asexual spores, which are produced by one parent only (through mitosis) and are genetically identical to that parent. Spores allow fungi to expand their distribution and colonize new environments. They may be released from the parent thallus, either outside or within a special reproductive sac called a sporangium.

There are many types of asexual spores. Conidiospores are unicellular or multicellular spores that are released directly from the tip or side of the hypha. Other asexual spores originate in the fragmentation of a hypha to form single cells that are released as spores; some of these have a thick wall surrounding the fragment. Yet others bud off the vegetative parent cell. Sporangiospores are produced in a sporangium.

Sexual Reproduction

Sexual reproduction introduces genetic variation into a population of fungi. In fungi, sexual reproduction often occurs in response to adverse environmental conditions. Two mating types are produced. When both mating types are present in the same mycelium, it is called homothallic, or self-fertile. Heterothallic mycelia require two different, but compatible, mycelia to reproduce sexually.

Although there are many variations in fungal sexual reproduction, all include the following three stages. First, during plasmogamy (literally, “marriage or union of cytoplasm”), two haploid cells fuse, leading to a dikaryotic stage where two haploid nuclei coexist in a single cell. During karyogamy (“nuclear marriage”), the haploid nuclei fuse to form a diploid zygote nucleus. Finally, meiosis takes place in the gametangia (singular, gametangium) organs, in which gametes of different mating types are generated. At this stage, spores are disseminated into the environment.


Reproduction in Fungi

Reproduction in fungi takes place by asexual or sexual means. Production of spores is observed in both these types of reproduction, though the genetic makeup of the spores varies. Read on to know more about the procreation process of fungi in this BiologyWise article.

Reproduction in fungi takes place by asexual or sexual means. Production of spores is observed in both these types of reproduction, though the genetic makeup of the spores varies. Read on to know more about the procreation process of fungi in this BiologyWise article.

Studying about the characteristics of fungi is quite fascinating. Beginning from the simple structure to the complex mode of reproduction, they represent one of the most diverse species of eukaryotic organisms. Fungi are present in any kind of habitat. To be more precise, they are ubiquitous in distribution. Recent studies have led to the conclusion that fungi (singular fungus) are more closely related to animals, rather than plants. Hence, they are categorized in a separate group, different from those of microbes, plants, and animals. The branch of biology that deals with the study of fungi is called mycology.

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Unlike plants, fungi lack the photosynthetic pigment (chlorophyll) and depend on others for food. They play a major role in decomposing the dead organisms and cleaning the environment, to make a sustainable place for other living entities. The versatile mode of reproduction in fungi is also responsible for their vast occurrence. Take the example of fungal reproduction by formation of spores. The spores are lightweight and disperse easily from one place to another, through wind, water, or other agents. In favorable conditions, the fungal spores germinate and develop into new fungi.

Fungal Reproduction: An Overview

Can you believe that more than 100,000 species of fungi have been identified scientifically? An exclusive example of fungi is mushroom, which all of us are acquainted with. They may either be edible or poisonous. Other familiar types of fungi are mold, yeast, rusts, etc. Fungi reproduce both sexually and asexually. Nevertheless, the mode of reproduction varies from one phyla to another. In fact, fungi are differentiated with respect to the spore type and sexual reproduction strategy. Following is some brief information concerning asexual and sexual reproduction of this life form.

Asexual Reproduction

This means of procreation is observed more frequently than sexual reproduction. Nearly all types of fungi have the ability to reproduce asexually. This in turn accounts for its widespread distribution. At a time, millions of asexual spores are released, and when these spores land on a fertile environment, they germinate into new individuals. The various types of asexual reproduction in fungi are spore formation, fragmentation, budding, and fission.

Out of these, vegetative spores or conidia are the most prevalent types. Under asexual spore formation, the fungal hyphae produces spores, either internally or externally. Fragmentation, as the term signifies, involves breaking of the fungal mycelium into several fragments. Each of the fragmented parts then develop into a new fungus. In case of budding, the parental cell protrudes a bud-like structure that bears the daughter nuclei. This bud breaks off and then grows into a new fungus.

Sexual Reproduction

Fungi reproduction by the sexual method is very complex. Though the basic phenomenon for fusion of male and female gametes remain the same, differences are observed amongst various types of fungi. As a part of the initiation phase in sexual reproduction cycle, compatible haploid hyphae come together. Subsequently, the male and female cells combine together, resulting in the formation of fertile diploid cells called spores. The spores are then released into the environment.

Except for glomeromycetes, sexual reproduction is observed in all kinds of fungi. As you can see, spores are produced in both asexual and sexual types of reproduction for this life form. The difference, however, lies in the genetic makeup of the spores. While those formed during asexual reproduction are vegetative, spores formed after sexual reproduction contain genomes of the parental fungal hyphae.

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Reproduction in fungi

Each of the fungal groups is characterized by differences in their life cycles. All fungi are characterized by having a period of vegetative growth where their biomass increases. The length of time and the amount of biomass needed before sporulation can occur vary. Almost all fungi reproduce by the production of spores, but a few have lost all sporing structures and are referred to as mycelia sterilia. Different types of spore are produced in different parts of the life cycle.

▶Reproduction in the Chytridiomycota and related taxa

Fungi in the Chytridiomycota and related groups are quite distinct from other fungi as they have extremely simple thalli and motile zoospores. Some species within this group can be so simple that they consist of a single vegetative cell within (endobiotic) or upon (epibiotic) a host cell, the whole of which is converted into a sporangium, a structure containing spores. These types are termed holocarpic forms.

Other members of this group have a more complex morphology, and have rhizoids and a simple mycelium. Asexual reproduction in the Chytridiomycota is by the production of motile zoospores in sporangia that are delimited from the vegetative mycelium by complete septae. The zoospores have a single, posterior flagellum. Sexual reproduction occurs in some members of the Chytridiomycota by the production of diploid spores after either somatic fusion of haploid cells, or fusion of two different mating-type mycelia, or fusion of two motile gametes, or fusion of one motile gamete with a nonmotile. The resulting spore may undergo meiosis to produce a haploid mycelium or it may germinate to produce a diploid vegetative mycelium, which can undergo asexual reproduction by the production of diploid zoospores. The diploid mycelium can also produce resting sporangia in which meiosis occurs, generating haploid zoospores that germinate to produce haploid vegetative mycelium.

Life cycle of Batrachochytrium dendrobatidis

▶Reproduction in the Zygomycota

In the Zygomycota, asexual reproduction begins with the production of aerial hyphae. The tip of an aerial hypha, now called a sporangiophore, is separated from the vegetative hyphae by a complete septum called a columella. The cytoplasmic contents of the tip differentiate into a sporangium containing many asexual spores. The spores contain haploid nuclei derived from repeated mitotic divisions of a nucleus from the vegetative mycelium. Dispersal of the spores is by wind or water. In sexual reproduction, two nuclei of different mating types fuse together within a specialized cell called a zygospore. In some species the different mating-type nuclei may be within one mycelium (homothallism). In other species, two mycelia with different mating-type nuclei must fuse (heterothallism). In both cases, fusion occurs between modified hyphal tips called progametangia, which once fused are termed the zygospore. Within the developing zygospore meiosis occurs usually three of the nuclear products degenerate, leaving only one nuclear type present in the germinating mycelium.

▶Reproduction in the Glomeromycota

The Glomeromycota are a monophyletic group, distinct from the Zygomycota on the basis of their symbiotic habit, lack of zygospores, and their rDNA phylogeny. No sexual reproduction has been detected in this group and their life cycle is characterized by germination of large mitospores in soil followed by growth of the germ tube towards a compatible plant root. Once in contact, the germ tube forms an appressorium, a cushion-like structure that aids penetration of the fungus into the root cells, and from the penetration site a number of parasitic structures develop within the root. New spores are formed inside the root and/or in the soil.

▶Reproduction in the Dikarya: Ascomycota

The vegetative stage of the Ascomycota life cycle is accompanied or followed by asexual sporulation by the production of single spores called conidia from the tips of aerial hyphae called conidiophores. The spores can be delimited by a complete transverse wall formation followed by spore differentiation termed thallic spore formation, or more usually by the extrusion of the wall from the hyphal tip, termed blastic spore formation. These spores can be single-celled and contain one haploid nucleus, or they can be multicellular and contain several haploid nuclei produced by mitosis.

Spores can be produced from single, unprotected conidiophores or they can be produced from aggregations that are large enough to be seen with the naked eye. The conidiophores can aggregate into stalked structures where the spores produced are exposed at the top (synnema or coremia). Alternatively, varying amounts of sterile fungal tissue can protect the conidia, as in the flask-shaped pycnidia. Some species produce conidia in plant tissue, and the conidial aggregations erupt through the plant epidermis as a cup-shaped acervulus or a cushion-shaped sporodochium.

Sexual reproduction in this group occurs after somatic fusion of different mating-type mycelia. A transient diploid phase is rapidly followed by the formation of ascospores within sac-shaped asci differentiated from modified hyphal tips. In the initial stages of ascal development hooked hyphal tips form, called croziers or shepherds’ crooks because of their shape. They have distinctive septae at their base, which insure that two different mating-type nuclei are maintained in the terminal cell. Formation of the septae is co-ordinated with nuclear division. In yeasts all these events occur within one cell, after fusion of two mating-type cells, the whole cell being converted into an ascus.

In more complex Ascomycota many asci form together, creating a fertile tissue called a hymenium. In some groups the hymenium can be supported or even enclosed by large amounts of vegetative mycelium. The whole structure is called a fruit body or sporocarp and is used as a major taxonomic feature. They can become large enough to be seen with the naked eye. Flask-shaped sexual reproductive bodies are called perithecia, cup-shaped bodies are called apothecia, and closed bodies are called cleistothecia. These structures have evolved to protect the asci and assist in spore dispersal, but the hymenium itself is unaffected by the presence of water.

▶Reproduction in the Dikarya: Basidiomycota

This group of fungi is characterized by the most complex and large structures found in the fungi. They are also distinctive in that they very rarely produce asexual spores. Much of the life cycle is spent as vegetative mycelium, exploiting complex substrates. A preliminary requisite for the onset of sexual reproduction is the acquisition of two mating types of nuclei by the fusion of compatible hyphae. Single representatives of the two mating type nuclei are held within every hyphal compartment for extended periods of time. This is termed a dikaryotic state, and its maintenance requires elaborate septum formation during growth and nuclear division.

Onset of sexual spore formation is triggered by environmental conditions and begins with the formation of a fruit body primordium. Dikaryotic mycelium expands and differentiates to form the large fruit bodies we recognize as mushrooms and toadstools. Diploid formation and meiosis occur within a modified hyphal tip called a basidium.

Four spores are budded from the basidium. Basidia form together to create a hymenium, which is highly sensitive to the presence of free water. The hymenium is distributed over sterile, dikaryotic-supporting tissues that protect it from rain. The hymenium can be exposed on gills or pores beneath the fruit body, seen in the toadstools and bracket fungi, or enclosed within chambers as in the puffballs and truffles.

▶Fungal spores

Fungi have two conflicting requirements for their spores. Spores must allow fungi to spread, but they must also allow them to survive adverse conditions. These requirements are met by different types of spores. Small, light spores are carried furthest from parent mycelium in air and these are the dispersal spores. They are usually the products of asexual sporulation, the sporangiospores and the conidiospores, and so spread genetically identical individuals as widely as possible. Genetic diversity is maintained by sexual reproduction, and the spore products are often large resting spores that withstand adverse conditions but remain close to their site of formation. Spores therefore vary greatly in size, shape, and ornamentation, and this variation reflects specialization of purpose.

▶Spore discharge

Spores that have a dispersal function can be released from their parent mycelium by active or passive mechanisms. As many spores are wind-dispersed, they are produced in dry friable masses that are passively discharged by wind. Other spores are passively discharged by water droplets splashing spores away from parent mycelium. Fungal spores can be actively discharged by explosive mechanisms. These mechanisms use a combination of an increasing turgor pressure within the spore-bearing hypha, combined with an inbuilt weak zone of the hyphal wall. This ensures that when the hypha bursts the spore discharge is directed for maximum distance. Asci are usually dispersed in this way, and a few sporangia too. Basidiospores are also actively discharged.

Airborne fungal spores can be carried great distances. Their presence in the air can have an impact on human health as they can cause allergic rhinitis (hay fever) and asthma. Many plant diseases that cause significant economic losses are airborne. Spore clouds can be tracked across continents, and epidemic disease forecasts can be made, depending on weather conditions and counts of air spora.


Reproducing Yeast Cell Diagram

Later the nucleus of the parent yeast is separated into two parts and one of the nuclei shifts into. Yeasts like all fungi may have asexual and sexual reproductive cycles.



Budding Asexual Reproduction Of Yeast Cell Cross Section Of Royalty Free Cliparts Vectors And Stock Illustration Image 124341496

Most reproduce asexually by mitosis and many do so via an asymmetric division process called budding.

Reproducing yeast cell diagram. The diagram below represents reproduction in a yeast cell. The genes in the bud are identical to the genes in the parent. Haploid cells with different gender fuse together to form a diploid yeast cell.

Each yeast cell has a distinct cell wall enclosing granular cytoplasm within which can be seen a large vacoule and a nucleus fig. Sexual reproduction of yeast. The genus pityrosporum is characterized by vegetative cells reproducing by repeated unipolar budding on a broad base.

Only haploid cells undergo sexual reproduction. It takes place by the formation of endospores during unfavourable conditions. Haploid cells undergo a process called shmooing in which they become longer and thinner while preparing to join.

The structure of yeast cell has been very thoroughly worked out by a large number of investigators who differ in their interpretations. 217a b the nucleus divides into two daughter nuclei and gradually a transverse partition wall is laid down somewhat near the middle starting from periphery to the centre dividing the mother cell into two daughter cells fig. Under starved conditions the nucleus of the yeast cell divides mitotically into four nuclei.

217 c d. Yeasts are eukaryotic micro organisms classified in the kingdom fungi with 1500 species currently described estimated to be only 1 of all fungal species. Yeast cells reproduce asexually by an asymmetric division process called budding.

This structure is called endospore fig. Yeasts are unicellular although some species with yeast forms may become multicellular through the formation of a string of connected. In one genus trigonopsis yeast cells have a triangular shape with budding restricted to the 3 apices.

During reproduction of fission yeasts the parent cell elongates fig. In yeast budding usually occurs during the abundant supply of nutrition. This type of production of offspring is a form of.

The fusion of haploid yeast cells is called sexual conjugation or mating. The nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell. The most common mode of vegetative growth in yeast is asexual reproduction by budding where a small bud also known as a bleb or daughter cell is formed on the parent cell.

In this process of reproduction a small bud arises as an outgrowth of the parent body. Cytoplasm gathers around the nucleus and each develops a thick wall. The bud then continues to grow until it separates.

This type of budding causes the vegetative cell to assume a lemon shape and the yeasts are known as apiculates. In this process parent cell become elongated and transverse wall is formed at centre due to which parent cell divides into daughter cell and each daughter cell live at new yeast cell.



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24.1C: Fungi Reproduction - Biology

Fungi reproduce by vegetative, asexual and sexual methods.

Vegetative reproduction:

Fragmentation

In many fungi, hyphae get broken into fragments accidentally. Each fragment in suitable conditions, develop into a new individual mycelium. It occurs frequently in nature.

In this method, a soft zone appears on the cell wall of the vegetative cell which bulges out and is called the bud. The bud finally is detached from the mother cell by a constriction and forming a new cell. This chain appears like mycelium and is called pseudo mycelium.

In fission, the vegetative cell splits into two daughter cells followed by constriction. Each daughter cell develops into a new individual vegetative cell.

Asexual reproduction

Zoospores are thin-walled, uninucleate motile spores formed in zoosporangium. They are naked spores without cell wall which after swarming period encysts. Eg Pythium

Aplanospores

Aplanospores are non-motile, thin-walled spores produced in the sporangium. They liberate from sporangium and germinate into new mycelium. Eg mucor

In some true fungi, the hyphae split up into numerous small oval or rounded fragments known as oidia. Each oidium germinates to a new mycelium.

Chlamydospores

In some fungi, thick-walled, resistant spores are formed from terminal or intercalary cells which are called Chlamydospores. They are released after the death of hyphae. In return of favourable condition, they germinate to new mycelia. Eg Pythium, Mucor, etc.

Conidia are non-motile, thin walled exogenous spores produced on a conidiophore. They have formed singly in Pythiumor in chain Penicillium.

Asexual reproduction in fungi --(A) Zoospores , (B) Sporangiospores (Aplanosporesa), (C) Chlamydospores , (D) Oidia , (E) Conidia

Sexual reproduction

Most of the true fungi reproduce sexually except fungi imperfect. The sexual reproduction involves three principal events.

Plasmogamy is the process which brings the fusion of cytoplasm of two different cells. It brings two genetically different nuclei in the same cell. Such a cell with two nuclei is called dikaryotic. and a pair of two such different nuclei is called dikaryon.

Karyogamy is the second phase of the sexual reproduction. It involves the fusion of two haploid nuclei to form a diploid zygote. Karogamy takes place either immediately or after the plasmogamy. In higher fungi, karyogamy is somewhat delayed. The dikaryotic mycelium has a long vegetative phase in higher fungi.

This is the third phase of sexual reproduction. In it, the diploid nucleus undergoes meiosis to produce the haploid nuclei. It also helps in the recombination of genetic material. The product of meiosis is called meiospores. Meiospores act as sexual spores which germinate into mycelium.

Sex organs

In fungi, the sex organs are called gametangia which are unicellular and naked. Gametangia develop on different hyphae of the same mycelium as homothallism or on different mycelia as heterothallism. The sexual reproduction in fungi takes place in following ways

Gametic fusion

It involves the fusion of two motile or non-motile gametes. It forms the diploid zygote. It is of three types

In this type, the fusing gametes are morphologically similar in size and shape but physiologically different. The gametes are called isogametes and their fusion is called isogamy.

In this type of fusion, the fusing gametes are morphologically as well as physiologically different. The male gamete is more active and small while the female gamete is larger and less active.

It is the most advanced type of gametic fusion. Out of the two fusing gametes, the female gamete is non-motile and is called an egg, and the male gamete is called the sperms. This type of reproduction is oogamy.

Different types of sexual reproduction in fungi - (A) Planogametic (Gametic fusion), (B) Spermatogamy, (C) Gametangial copulation, (D) Gametangial contact, (E) Somatogamy

Spermatization

In this type, numerous uninucleate, unicellular, non-motile male cells called spermatia are borne externally or inside the cavities or hyphae. These spermatia are carried to the female gametangia by various agents like wind, water etc. A pore is developed at the point of contact and the contents of spermatium are transferred to the receptive hyphae and form a dikaryon.

Gametangial copulation

In this type, the entire protoplasts of anisogamete are involved in fusion and thick-walled body formed which is called zygospore. It is common in fungi like Mucor, Rhizopus.

Gametangial contact

In this type the male and female gametangia come in contact with one another. The entire protoplast of male gametangium passes into the oogonium either through a pore formed at the point of contact or through one or more fertilisation tube that arises from male gametangium.

Somatogamy

Somatogamy takes place by the fusion between undifferentiated vegetative cells of the same thallus or two different thalli in higher fungi like yeast. In them, the formation of gametes is absent.

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Things to remember
  • The product of meiosis is called meiospores.
  • Each fragment in suitable conditions develops into a new individual mycelium.
  • Somatogamy takes place by the fusion between undifferentiated vegetative cells of the same thallus or two different thalli in higher fungi like yeast.
  • Meiospores act as sexual spores which germinate into mycelium.
  • In some fungi, thick-walled, resistant spores are formed from terminal or intercalary cells which are called Chlamydospores.
  • Plasmogamy is the process which brings the fusion of cytoplasm of two different cells.
  • It includes every relationship which established among the people.
  • There can be more than one community in a society. Community smaller than society.
  • It is a network of social relationships which cannot see or touched.
  • common interests and common objectives are not necessary for society.

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Reproduction of Fungi

The majority of fungi can reproduce both asexually and sexually. This allows them to adjust to conditions in the environment. They can spread quickly through asexual reproduction when conditions are stable. They can increase their genetic variation through sexual reproduction when conditions are changing and variation may help them survive.

Asexual Reproduction

Almost all fungi reproduce asexually by producing spores. A fungal spore is a haploid cell produced by mitosis from a haploid parent cell. It is genetically identical to the parent cell. Fungal spores can develop into new haploid individuals without being fertilized.

Spores may be dispersed by moving water, wind, or other organisms. Some fungi even have &ldquocannons&rdquo that &ldquoshoot&rdquo the spores far from the parent organism. This helps to ensure that the offspring will not have to compete with the parent for space or other resources. You are probably familiar with puffballs, like the one in Figure below. They release a cloud of spores when knocked or stepped on. Wherever the spores happen to land, they do not germinate until conditions are favorable for growth. Then they develop into new hyphae.

Puffballs release spores when disturbed.

Yeasts do not produce spores. Instead, they reproduce asexually by budding. Budding is the pinching off of an offspring from the parent cell. The offspring cell is genetically identical to the parent. Budding in yeast is pictured in Figure below.

Yeast reproduce asexually by budding.

Sexual Reproduction

Sexual reproduction also occurs in virtually all fungi. This involves mating between two haploid hyphae. During mating, two haploid parent cells fuse, forming a diploid spore called a zygospore. The zygospore is genetically different from the parents. After the zygospore germinates, it can undergo meiosis, forming haploid cells that develop into new hyphae.


Chapter Summary

Fungi are eukaryotic organisms that appeared on land more than 450 million years ago, but clearly have an evolutionary history far greater. They are heterotrophs and contain neither photosynthetic pigments such as chlorophyll, nor organelles such as chloroplasts. Fungi that feed on decaying and dead matter are termed saprobes. Fungi are important decomposers that release essential elements into the environment. External enzymes called exoenzymes digest nutrients that are absorbed by the body of the fungus, which is called a thallus. A thick cell wall made of chitin surrounds the cell. Fungi can be unicellular as yeasts, or develop a network of filaments called a mycelium, which is often described as mold. Most species multiply by asexual and sexual reproductive cycles. In one group of fungi, no sexual cycle has been identified. Sexual reproduction involves plasmogamy (the fusion of the cytoplasm), followed by karyogamy (the fusion of nuclei). Following these processes, meiosis generates haploid spores.

24.2 Classifications of Fungi

Chytridiomycota (chytrids) are considered the most ancestral group of fungi. They are mostly aquatic, and their gametes are the only fungal cells known to have flagella. They reproduce both sexually and asexually the asexual spores are called zoospores. Zygomycota (conjugated fungi) produce non-septate hyphae with many nuclei. Their hyphae fuse during sexual reproduction to produce a zygospore in a zygosporangium. Ascomycota (sac fungi) form spores in sacs called asci during sexual reproduction. Asexual reproduction is their most common form of reproduction. In the Basidiomycota (club fungi), the sexual phase predominates, producing showy fruiting bodies that contain club-shaped basidia, within which spores form. Most familiar mushrooms belong to this division. Fungi that have no known sexual cycle were originally classified in the “form phylum” Deuteromycota, but many have been classified by comparative molecular analysis with the Ascomycota and Basidiomycota. Glomeromycota form tight associations (called mycorrhizae) with the roots of plants.

24.3 Ecology of Fungi

Fungi have colonized nearly all environments on Earth, but are frequently found in cool, dark, moist places with a supply of decaying material. Fungi are saprobes that decompose organic matter. Many successful mutualistic relationships involve a fungus and another organism. Many fungi establish complex mycorrhizal associations with the roots of plants. Some ants farm fungi as a supply of food. Lichens are a symbiotic relationship between a fungus and a photosynthetic organism, usually an alga or cyanobacterium. The photosynthetic organism provides energy from stored carbohydrates, while the fungus supplies minerals and protection. Some animals that consume fungi help disseminate spores over long distances.

24.4 Fungal Parasites and Pathogens

Fungi establish parasitic relationships with plants and animals. Fungal diseases can decimate crops and spoil food during storage. Compounds produced by fungi can be toxic to humans and other animals. Mycoses are infections caused by fungi. Superficial mycoses affect the skin, whereas systemic mycoses spread through the body. Fungal infections are difficult to cure, since fungi, like their hosts, are eukaryotic, and cladistically related closely to Kingdom Animalia.

24.5 Importance of Fungi in Human Life

Fungi are important to everyday human life. Fungi are important decomposers in most ecosystems. Mycorrhizal fungi are essential for the growth of most plants. Fungi, as food, play a role in human nutrition in the form of mushrooms, and also as agents of fermentation in the production of bread, cheeses, alcoholic beverages, and numerous other food preparations. Secondary metabolites of fungi are used as medicines, such as antibiotics and anticoagulants. Fungi are model organisms for the study of eukaryotic genetics and metabolism.


During asexual reproduction, some hyphae become spore-producing bodies called sporangia or conidia. The group of fungi known as Zygomycota develop sporangia within a sac. This sac then bursts to release the spores. Once the spores land on a suitable habitat, they germinate a new hypha that grows into a mycelium. In the fungi groups Ascomycota and Basidiomycota, spores called conidia are not held within a sac. Once the spores disperse they will germinate and form a new mycelium. Ascomycota includes fungi such as the one responsible for athlete's foot Basidiomycota includes fungi such as mushrooms.

Some fungi that reproduce asexually can also reproduce sexually. In sexual reproduction, the hyphae of individual fungi meet and join together to become what is called a gametangia in a process known as plasmogamy. Within the gametangia, the nuclei from the cells of the two individuals fuse. This process -- karyogamy -- combines and mixes up the DNA from the two individuals. Karyogamy produces a spore that has double the normal number of chromosomes. In meiosis, this diploid spore halves itself to create two spores each with the normal number of chromosomes. Zygomycota, Ascomycota and Basidiomycota each reproduce sexually. The difference is the structure the spores form in. Basidiomycota form fruiting bodies called mushrooms or basidius Ascomycota have sacs called ascus and Zygomycota produce zygospore.


Antifungal resistance: an overlooked killer

The advancement of modern medicine has emerged with many challenges. The misuse and overuse of antibiotics is a familiar concept to all. Antimicrobial resistance (AMR) is a term which has been in the limelight for the past several decades, with growing focus on antibacterial resistance. However, problems associated with antifungal resistance, which is equally as deadly, have often been overlooked (Helen Albert, 20202). In 2018, the UK government put aside £20 million out of £30 million to fund antibiotic resistance related research and development. A mere £5 million was used to fund an AMR research group looking at the impact of antimicrobial resistance in agriculture and the environment (GOV.UK, 2020). Life threatening systemic fungal infections are on the rise, with mortality rates reported to have risen from 35% to 80% with current standard of care. Fungi have clearly developed the ability to win the battle against the drugs designed to kill them, rendering the antifungal drugs ineffective (Centers for Disease Control and Prevention, 2020). As fungi share the eukaryotic domain with humans, similarities make it difficult to develop new nontoxic antifungal drugs, an issue less prevalent with other microbes such as bacteria which are less closely related to humans (Helen Albert, 2020). With opportunistic fungal infections becoming an increasing threat globally, especially with the rising number of immunocompromised COVID-19 patients, funding for the development of promising new drugs is imperative.

Fungi exist in two forms: yeasts and moulds. Asexual reproduction of fungi involves production of microscopic spores (Biology Libre Texts, 2020). These spores spread in soil and air, enabling contact with humans via inhalation or via contact with skin. As a result, fungal infections often start in the lungs or on the skin (S.G. Revankar, 2020). It is fairly common for mild fungal infections to take place, e.g. under the nails. However, humans have developed a somewhat natural resistance to these types of infections. Severe fungal infections which require therapeutic intervention arise when patients are immunocompromised due to previous diseases or use of immunosuppressants. Additionally, introduction of foreign material into the body, for example during surgery, can trigger severe fungal infections (S.G. Revankar, 2020). These opportunistic infections include aspergillosis, candidiasis and mucormycosis all caused by entry of different types of fungi (Aspergillus, Candida and moulds) into various body parts (S.G Revankar, 2020).

The only readily available treatment for fungal infections at the moment is antifungal drugs.

Improper use of these drugs, in addition to the longevity of usage (patients have to be treated for several months with the same drug), has led to resistance among fungal species (Centers for Disease Control and Prevention, 2020). Alternatively, some fungal species are naturally resistant to certain types of antifungal drugs (Centers for Disease Control and Prevention, 2020). This antifungal resistance poses a great threat to suffering patients as their choice of treatment is already limited with only three types of antifungal drugs available on the market: polyenes, azoles, and echinocandins (Helen Albert, 2020). These drugs differ in their sites of action and targets. Polyenes and azoles work by altering the permeability of the fungal cell membrane which creates pores facilitating leakage of cellular contents, ultimately resulting in cellular apoptosis (Med Made Sirius-ly easy!, 2019). The function of echinocandins is to block b-glucan synthesis – an essential fungal cell wall component (Med Made Sirius-ly easy!, 2019). Using these different mechanisms of action, antifungal drugs are able to stop the spread of these deadly killers – however, they do each have their own limitations, reducing their applicability. The most commonly used polyene is a drug called amphotericin B. Resulting approval of this drug in the 1950s drastically improved patient’s survival prospects, however, recent developments have shown that the drug is associated with serious side effects such as kidney problems (Helen Albert, 2020). Azoles have been regarded the most successful antifungal drug to date after approval in the 1980s. Nonetheless, they come with their own problems such as their ability to inhibit cytochrome p450 – a detoxifying enzyme essential for maintaining normal blood homeostasis (Helen Albert, 2020). Echinocandin use is not associated with internal problems of the body, however, the once-a-day dosage required for patients is considered a liability – especially when patients require month-long treatments at any given time (Helen Albert, 2020).

Examples of resistant fungi include Candida Auris, which can develop resistance to all three drug types, and Aspergillus, which is resistant to azole drug fluconazole (Centers for Disease Control and Prevention, 2020). Excessive use of azoles in agriculture has accelerated fungal resistance. This is a particularly prevalent issue in the Netherlands – home to many flower farms where the common fungus Aspergillus resides. Aspergillus has the ability to cause severe damage to immunocompromised individuals. Farmers in the Netherlands spray their fields continuously with low concentrations of azoles and as a result, Netherlands has one of the highest rates of azole-resistant invasive aspergillosis in the world (Helen Albert, 2020). Fungal resistance is particularly concerning for patients with serious infections of the blood, heart, brain, eyes and other parts of the body as it is difficult to eradicate the infections with such limited treatment options available (Centers for Disease Control and Prevention, 2020). This highlights the need for new drugs in the pipeline.

The future of the antifungal space is very exciting. The COVID-19 pandemic this year has helped to highlight the importance of this area of drug development. Four biotech companies are currently testing novel antifungals in the phase II and phase III trials stage fosmanogepix from US biotech Amplyx, rezafungin from California-based Cidara, olorofim from UK biotech F2G and ibrexafungerp from New Jersey-based Scynexis (Helen Albert, 2020). Rezafungin and ibrexafungerp are both more advanced in phase III trials, with olorofilm and fosmanogepix close behind in phase II trials (Helen Albert, 2020). Rezafungin is the newest addition to the echinocandin class (Helen Albert, 2020). It is an intravenous drug which will have to be administered once a week at a high dose as opposed to the current methods of treatment which are administered daily (Helen Albert, 2020). It is able to be given at a high dose because it doesn’t break down and thus does not induce unwanted liver toxicity (Helen Albert, 2020). Ibrexafungerp is the most advanced novel antifungal drug currently being developed (Helen Albert, 2020). It will be orally administered which is advantageous as patients will be allowed to be discharged whilst taking the treatment (Helen Albert, 2020). Olorofilm is the first drug in the orotomide drug class (Helen Albert, 2020). It halts fungal growth by inhibiting pyrimidine synthesis and targeting fungal enzyme dihydroorotate dehydrogenase (Helen Albert, 2020). Fosmanogepix also targets another enzyme specific to fungi called Gwt1 (Helen Albert, 2020). This specificity ensures that the drug does not cause any adverse effects in humans (Helen Albert, 2020). Fungi are no longer able to evade the immune system after fosmanogepix is given as a treatment (Helen Albert, 2020). In trials to date, these four drugs have shown broad efficacy and promising data. However, drug development and clinical trials are time consuming processes but with the perseverance of these four companies there is reason to be hopeful for the future of this sector.


Reproduction of Fungi

Fungi reproduced by vegetative, asexual, and sexual means. The asexual reproduction predominant which Depends upon the involvement of the entire thallus or a part of it, the fungi can be holocarpic or eucarpic.

Holocarpic fungi

In Holocarpic fungi, the whole thallus is converted into one or more reproductive bodies. The vegetative and reproductive phase does not occur at the same time in Holocarpic fungi.

Eucarpic fungi

In eucarpic fungi, only one part of the thallus develops reproductive organs whereas the remaining parts remain in the vegetative stage. Most of the fungi are Eucarpic in nature, where the vegetative and reproductive stages occur at the same time.

Vegetative Reproduction

In vegetative reproduction, one part of mycelium gets separated from the parent body and forms a new individual. The vegetative reproduction is accomplished by different methods such as fragmentation, budding, fission, sclerotia, rhizomorphs, and oidia formation.

The hyphae of Rhizopus and Coprinus is fragmented into many small fragments and then each of them gives rise to a new mycelium.

Asexual Reproduction

Types of Fungi and Their Reproduction – Spores

The Asexual Reproduction of fungi is accomplished by spores, either motile or non-motile, and form in a specialized part of mycelium. In asexual reproduction, fungi develop different types of spores such as zoospores, sporangiospores (=aplanospores), conidia, oidia (arthrospores), chlamydospores, gemmae, ascospores, uredospores, basidiospores etc.

Types of Fungi and Their Reproduction – vegetative reproduction

Sexual Reproduction

Sexual Reproduction is accomplished by the formation and fusion of gametes. Except Deuteromycetes or fungi imperfecti, sexual reproduction is found in all groups of fungi.

Sexual reproduction is accomplished in three distinct phases such as plasmogamy (protoplasmic fusion), karyogamy (fusion of nuclei), and meiosis (reduction division of zygote).

Different Methods of sexual Reproduction in Fungi

(i) Planogametic copulation

In Planogametic copulation two gametes of opposite sex or strains are fused, where one or both of the fusing gametes are motile (flagellated). As a result of Planogametic copulation, it forms a diploid zygote.

Planogametic copulation is two type such as

In this process, the fusion occurs between two morphologically similar and motile but physiologically dissimilar gametes, which are produced by different parents

(b) Heterogamy

In this process, the fusion occurs between two morphologically as well as physiologically different gametes. Heterogamy is divided into two classes such as Heterogamous reproduction is of two types: anisogamy and oogamy.

In Anisogamy the fusion occurs between two motile gametes where the male gamete is small and more active than the female gamete. Example: Allomyces.

In oogamy, the fusion occurs between the motile male gamete (antherozoid) with the large, non-motile female gamete (egg or ovum). Example: Monoblepharis, Synchytrium etc.

(ii) Gametangial contact

This method is accomplished between two gametangia of the opposite sex. In Gametangial contact, the male gametangium (antheridium) transfer it’s male nucleus or gamete into the female gametangium (oogonium) either through a pore or through a fertilization tube.

Example: Phytophthora, Sphaerothera, Alb. go, Pythium etc.

(iii) Gametangial copulation

In this method, the entire contents of two gametangia fused to form a common cell known as zygote or zygospore.

(iv) Spermatization

In this method, the fungi develop many minute, spore-like, single-celled structures called spermatia (nonmotile gametes). After that, these minute structures are transferred to either special receptive hyphae or trichogyne of ascogonium through the water, wind, and insects. The contents migrate into receptive structure. Thus dikaryotic condition is established.

(v) Somatogamy

In this method, the formation of the gametes is absent. The hyphae and their somatic cells are fused and form a dikaryotic cell.

Example: Agaricus, Peniophora etc.

Types of Fungi and Their Reproduction – sexual reproduction