11th Class Biology Biological Classification And System Of Classification / जैविक वर्गीकरण और वर्गीकरण की प्रणाली Reproduction

(1) Vegetative reproduction

Fragmentation : Some forms belonging to Ascomycotina and Basidiomycotina multiply by breakage of the mycelium.

Budding : Some unicelled forms multiply by budding. A bud arises as a papilla on the parent cell and then after its enlargement separates into a completely independent entity.

Fission : A few unicelled forms like yeasts and slime molds multiply by this process.

(2) Asexual reproduction

Oidia : In some mycelial forms the thallus breaks into its component cells. Each cell then rounds up into a structure called oidium (pl. oidia). They may germinate immediately to form the new mycelium, e.g., Rhizopus.

Chlamydospores : Some fungi produce chlamydospores which are thick walled cells. They are intercalary in position. They are capable of forming a new plant on approach of favourable conditions, e.g., Rhizopus, Saprolengnia Ustilago.

Sporangiospores : These are thin-walled, non-motile spores formed in a sporangium. They may be uni-or multinucleate. On account of their structure, they are also called as aplanospores. e.g., Rhizopus, Mucor.

Zoospores : They are thin-walled flagellate spores which occur in aquatic fungi. These spores formed in a zoosporangium. The zoospores are of several types:

• Uniflagellate with whiplash type flagellum e.g., Allomyces.
• Uniflagellate with tinsel type flagellum e.g., Rhizidiomyces.
• Biflagellate with a tinsel type and a whiplash type flagella e.g., Saprolegnia.
• Biflagellate with two whiplash type flagella e.g., Plasmodiophora.

Conidia : In some fungi the spores are not formed inside a sporangium. They are born freely on the tips of special branches called conidiophores. The spores thus formed are called as conidia. e.g., Penicillium.

Bi-celled conidia are formed in Trichothecium. In Fusarium it is possible to differentiate smaller microconidia from larger macroconidia.

(3) Sexual reproduction : With the exception of Deuteromycetes (fungi imperfecti), the sexual reproduction is found in all groups of fungi. During sexual reproduction the compatible nuclei show a specific behaviour which is responsible for the onset of three distinct mycelial phases. The three phases of nuclear behaviour are as under :

Plasmogamy : Fusion of two protoplasts.

Karyogamy : Fusion of two nuclei.

Meiosis : The reduction division.

These three events are responsible for the arrival of the following three mycelial phases :

Haplophase : As a result of meiosis the haploid (n) or haplophase mycelium is formed.

Dikaryotic phase : The plasmogamy results in the formation of dikaryotic mycelium (n + n).

Diplophase : As a result of karyogamy the diplophase mycelium (2n) is formed.

In some fungi plasmogamy, karyogamy and meiosis do occur in a regular sequence but not at specified time or points in life cycle. Such a cycle is described as parasexual cycle and phenomena celled parasexuality recorded by Pontecorvo and Roper. 

The fungi reproduce sexually by the following methods

• Planogametic copulation : In this type of copulation fusion occur between flagellate gamete. It is of three types :

(i) Isoplanogametic copulation : Both the fusion gametes are similar and flagellate. e.g., Synchytrium.

(ii) Anisoplanogametic copulation : The fusing gametes are flagellate, similar in structure but different in size. In which one is small and other one is large. e.g., Allomyces.

(iii) Ooplanogametic copulation : It is union between a small flagellate male gamete and a large nonflagellate food laden female gamete or ovum. . e.g., Monoblepharella.

• Gametangial contact : It involves fusion of two gametangia. In lower forms the female gametangium is called as oogonium. The male gametangium is termed as antheridium. A contact develops in between the two gametangia and then the male nucleus is transferred into the female directly or through a tube. e.g., Phytophthora, Albugo.
• Gametangial copulation : In this case the fusion occurs in between the two gametangia. When it occurs in some holocarpic forms where the entire thallus acts as gametangium, the phenomenon is called as hologamy. In others, dissolution of cell wall in between the two gametagial brings about gametangial copulation. e.g., Rhizopus, Mucor.
• Spermatization : Here the uninucleate male gametes called spermatia are formed in special structures called spermogonia or pycnidia. The female gametangium is called as ascogonium which has a long neck called trichogyne. The spermatium attaches itself with the trichogyne and transfers the male nucleus, thus bringing about dikaryotisation. e.g., Puccinia graminis.

Somatogamy : In higher fungi there is reduction of sexuality to the maximum level. Here two hyphae of opposite strains are involved in fusion thus bringing about dikaryotization. e.g., Penicillium brefeldianum, Agaricus.