Like algae, reproduction in fungi occurs through vegetative, asexual, and sexual methods. In the following account, we will describe the various types of production in fungi with suitable examples.

Reproduction in Fungi

Fungus hypha elongates by apical growth, but most parts of a fungus are potentially capable of growth. When the mycelium of a fungus reaches a certain stage of maturity and accumulates reserve food, it starts reproducing.

As in algae, reproduction in fungi is of three kinds: vegetative, asexual, and sexual reproduction.

Vegetative and asexual methods of reproduction which do not involve the fusion of nuclei or sex cells or sex organs are, however, clubbed by many mycologists into asexual methods of reproduction. Thus, they recognize only two methods, asexual and sexual.

1. Asexual Reproduction

In fungi, asexual reproduction is a more common method than sexual reproduction. It is usually repeated several times in a season. It takes place by the formation of special reproductive cells called spores.

The formation of spores in fungi is called sporulation. Each spore develops into a new mycelium. These spores are produced as a result of mitosis in the parent cell and hence they are also called mitospores.

The spores vary in color, shape and size, number, arrangement on hyphae, and in the way in which they are borne. They may be hyaline, green, yellow, orange, red, and brown to black in color and are minute to large in size.

In shape, they vary from globose to oval, oblong, and needle-shaped to helical. Thus an infinite variety of spores can be observed in fungi and you will find them very fascinating under the microscope.

Usually, the spores are unicellular. They may be uninucleate or multinucleate. Some fungi like Alternaria and Curvularia, they are multicellular. The mitospores produced in fungi are of two types, sporangiospores and conidia.

The sporangiospores are produced inside a sac-like structure called sporangium. The hypha bearing a sporangium is called sporangiophore. They are characteristically branched.

The sporangiospores may be motile or non-motile. The non-motile sporangiospores are called aplanospores – from Greek a, not + planets wanderer + spores seed, spore. These are characteristic of terrestrial species like Mucor and Rhizopus.

In aquatic fungi like Pythium of’ the Division Oomycota motile biflagellate sporangiospores are produced. These are called zoospores and the sporangium bearing them is called zoosporangium.

A zoospore is a motile spore lacking a cell wall. After a swarming period it secretes a wall and germinates to form a germ tube. In contrast to zoospores, the aplanospores have a definite spore wall and are dispersed by wind and insects.

The conidia are non-motile, deciduous mitospores formed externally as single separate cells. They develop either directly on the mycelium or on morphologically differentiated hyphae called conidiophores.

The conidiophores may be simple or branched, septate or aseptate. The conidia are produced singly e.g., Phytophthora or in chains at the tips of the conidiophores e.g. Aspergillus or at the tips of their branches e.g., Penicillium.

Often the conidiophores arise singly and are scattered in the mycelium. Sometimes they arise in specialized structures called fruiting bodies. According to their appearance they are termed as synnema, sporodochia, acervuli (sucer-shaped), pycnidia (flask-shaped, globular) or pustules.

2. Sexual Reproduction

The sexual stage in fungi is called the perfect state in contrast to the imperfect state which is the asexual stage. Sexual reproduction involves the fusion of two compatible sex cells or gametes of opposite strains.

Fungal sex organs are called gametangia. They may be equal in size. In many higher ascomycetes, morphologically different gametangia are formed. The male gametangia are called antheridia and the female ones ascogonia.

The fungus may be homothallic, that is, the fusing gametes come from the same mycelium or may be heterothallic, that is, the fusing gametes come from different strains of mycelia.

In fungi, sexual reproduction involves the following three phases: i) plasmogamy, ii) karyogamy, and iii) meiosis. These three processes occur in a regular sequence and at a specific time, during the sexual stage of each species.

Plasmogamy: It is the union of protoplasts of reproductive hyphae or cells, one from the male and the other from the female to bring about the nuclei of the two parents close together as a pair. However, the two nuclei do not fuse with each other.

Such a cell is called a dikaryon. The dikaryotic condition is unique to fungi and may continue for several generations as the two nuclei (dikaryon) divide simultaneously during cell division. These are passed on to the daughter hypha.

Karyogamy: The fusion of the two nuclei which takes place in the next phase is called karyogamy. It may immediately follow plasmogamy as in lower fungi, or it may be delayed for a long time as in higher fungi.

Meiosis: Karyogamy which eventually occurs in all sexually reproducing fungi is sooner or later followed by meiosis producing four genetically different spores.

We will now discuss plasmogamy in detail. There are different methods of plasmogamy in fungi.

Planogametic copulation: It involves fusion of two gametes. Like in algae sexual union in fungi may be isogamous, anisogamous or oogamous.

Anisogamy and oogamy are together called heterogamous sexual reproduction. Isogamy is the simplest type of sexual reproduction, where the fusing gametes are morphologically similar e.g. Olpidium and Catenaria.

Anisogamy, where the fusing gametes are dissimilar is found in one genus, Allomyces, a chitrid. In oogamy as you may recall the motile antherozoid enters oogonium and unites with egg or oosphere forming a zygote. Oogamy is seen in fungi like Pythium and Albugo.

Gametangial copulation: The two gametangia make contact and the entire contents of the two fuse together and become one e. g., Mucor and Rhizopus.

In some fungi the entire protoplast of one gametangium flows into the other through a pore. Among the two, the recipient is the female and the donor is the male.

Gametangial contact: The male gamete is not a separate entity but the nucleus in the antheridium represents the gamete. As you can see in the figure, the oogonium and antherididm form a contact through a tube and one or more nuclei inside the antheridium migrate into the oogonium. You may note that in this case the two gametangia do not fuse. It is observed in Penicillium.

SpermatizationThis mode is quite remarkable as the minute conidia like gametes called spermatia are produced externally on special hyphae called spermatiophore.

Spermatia may develop inside the cavities called spermatogonia. The female cell may be a gametangium, a specialised receptive hypha or even a vegetative hypha.

Somatogamy: In higher fungi like Ascomycetes and Basidiomycetes there is a progressive degeneration of sexuality. The entire process is very much simplified by the fusion of two mycelia which belong to opposite strains.

The post-fertilization changes result in the production of a fruiting body which is called ascocarp in Ascomycetes and basidiocarp in Basidiomycetes.

The gametangial fusion followed by the fusion of male and female nuclei results in diploid nuclei. Subsequently, reduction division occurs and haploid spores are formed. In fungi, the spores may be formed in specialized structures characteristic of a division.

In Ascornycetes the spores called ascospores are formed within the ascus (plur. Asci,). The asci reside enclosed within the fruiting body- the ascocarp.

According to the characteristics, the ascocarps are distinguished as cleistothecium (indehiscent) apothecium, (cup or saucer shaped), perithecium (flask-shaped) and pseudoperithecium.

In basidiomycetes, sexual spores are termed basidiospores which develop on club- shaped structure, called basidium.

In summary, fungi reproduce when the mycelium reaches a certain stage of maturity. Phytophthora. Intestans the crusal organism for potato blight or late blight of potato reproduces sexually and asexually.

Both the asexual and sexual phases alternate with each other depending on how favourable the weather condition is. Rhizopus, also a parasite, have a similar life cycle like Phytophthora

Fungi reproduce by vegetative, asexual and sexual methods. Vegetative reproduction takes place by fission, budding, fragmentation.

Asexual reproduction occurs more frequently then sexual method. The sporangiophores or conidiophores formed bear spores and conidia respectively.

In sexual reproduction, depending upon the species the entire thallus or a portion of it may take part in the formation of reproductive bodies.

Read Also: Fungal Morphology and Forms