Reproduction in Fungi
Fungi reproduce by vegetative, asexual and sexual methods.
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.
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 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.
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
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.
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
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
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.
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.
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 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.
- 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.
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