MODE OF REPRODUCTION IN FUNGI (Part-3) Sexual Reproduction

1. Sexual Reproduction

a. The sexual reproduction involves the union of male and female gametes or two gametangia 

b. It has three distinct phases. They are plasmogamy, karyogamy and meiosis.

c. The plasmogamy refers to the fusion of two protoplasts that brings two haploid nucle together.

d. As a result of plasmogamy a cell containing two haploid nuclei is formed. 

e. This cell is known as binucleate cell or dikaryotic cell. 

f. The two nuclei residing in that cell are known as a dikaryon. 

g. Plasmogamy may be carried out either by gametic union or gametangial contact.

h. The next phase is the karyogamy. During karyogamy the two haploid nuclei in a dikaryotic cell fuse together and form diploid nucleus (2N). 

I. This nucleus is called a synkaryon. This phase lasts for a short time. It is also known as diplophase.

j. Meiosis is the third phase in the sexual reproduction. The diploid nucleus undergoes re-duction division and gives rise to four haploid nuclei. 

k. Here the chromosome number in the diploid nucleus is reduced into a half. 

l. The cell containing the haploid nuclei forms haploid spores (N).

m. These spores give rise to new mycelia (N).

There are five types of sexual union in fungi. They are-

1. Planogametic copulation

2. Gametangial contact

3. Gametangial copulation

4. Spermatogamy

5. Somatogamy.

1. Planogametic Copulation

1. Planogametes are motile flagellate gametes. The union of male and female gametes one or both of them are motile is called planogametic copulation. It may be an isogamy, anisogamy or oogamy.

2. In isogamy, the two gametes involved in the fusion are similar in their structure and func-tion.                   Eg. Catenaria.

3. In anisogamy, one of the gametes is smaller and the other is larger, but both of them are flagellate and motile. Eg Allomyces.

4. In oogamy, the male gamete is smaller and motile, but the female gamete (egg) is larger and non-motile. Eg. Monoblepharis sps.

2. Gametangial Contact

1. In some cases, the sex organs are very much reduced into hyphal structure containing undifferentiated protoplasts. These hyphal structures do not release gametes out. They are known as gametangia

2. The two gametangia of opposite sex contact each other and one nucleus of male gamet. angium enters the female gametangium. Here plasmogamy does not take place. The fertilized female gametangium develops into a zygote. Eg. Pythium aphanidermatum.

3. Gametangial Copulation

1. Some fungi produce male and female gametangia.

2. When they approach each other, they produce a fertilization tube between the two. 

3. The male and female nuclei move towards each other through the fertilization tube and fuse together.

4. As a result of this fusion, a diploid zygote is formed in the fertilization tube.

5. In Rhizopus, the two gametangia directly fuse together and form a diploid zygote.