Reproduction in fungi: asexual and sexual methods

Asexual reproduction in fungi:

1. fission of somatic cell
2. Budding of somatic cell
3. Fragmentation or disjoining of hyphae
4. Asexual spore formation

1. Fission:

• In binary fission a mature cell elongates and its nucleus divides into two daughter nuclei.
• The daughter nuclei separates, cleaves cytoplasm centripetally in the middle till it divides parent protoplasm into two daughter protoplasm.
• A double cross wall is deposited in the middle to form two daughter cell.
• Ultimately the middle layer of double cross wall degenerates and daughter cells are separated.
• Examples: Saccharomyces pobbe, Psygosaccharomyces

2. Budding:

• The cell wall bulge out and softens in the area probably by certain enzymes brought by vesicles.
• The protoplasm also bulge out in this region as small protuberance.
• The parent nucleus also divides into two, one of the daughter nucleus migrates into bud, the cytoplasm of bud and mother remain continuous for some time
• As the bud enlarges, a septum is laid down at the joining of bud with mother cell. Then bud separates and leads independent life.
• Some time, bud starts reproducing while still attached with mother cell. This gives branching appearance.
• Budding is the typical reproductive characteristics of Ascomycetes.
• Examples: yeast

3. Fragmentation:

• In some fungi, fragmentation or disjoining of hyphae occurs and each hyphae become a new organism

4.  Asexual spore of fungi:

• Spore formation is the characteristic feature of fungi.
• Different fungi forms different types of spore,

Types of asexual spore:

i. Sporangiospore:

• These asexual spore are produced in a sac like structure called sporangia (singular;saprangium).
• Sporangium are produced at the end of special aerial hyphae called sporangiophore
• Sporangium contains large numbers of haploid spores, which are released by rapture of sporangial wall
• Examples: Rhizopus

ii. Conidiospore:

• Conidiospore or conidia are single celled, bicelled or multicelled structure born on the tip or side of aerial hyphal structure called conidiophore
• Conidia are different from sporangiospore as these are not produced inside sporangium or any sac like structure.
• Conidia are born singly or in chain
• Examples: Penicillium, Apergillus

iii. Arthrospore:

• Arthrospore are very primitive type of spore formed by the breaking up of fungal mycelium
• A spore is formed by separation followed by fragmentation of hyphae
• Examples: Trichosporium, Geotrichum, Coccididious imitis

iv. Chlamydospore:

• These are usually formed during unfavorable condition and are thick walled single celled spore, which are highly resistant to adverse condition.
• Hyphal cell or portion of hyphae contracts, loose water, round up and develops into thick walled chalmydospore.
• When favorable condition returns, each chlamydospore give rise to a new individual fungi.
• Examples: ascomycetes, basidiomycetes, zygomycetes,
• Histoplasma capsulatum, Candida albicans

v. Blastospore:

• It is a budding spores usually formed at the terminal end of hyphae.
• These spore may remains attached to hyphae and bud further to gibe branching chain of blastospores
• Examples: ascomycetes, basidiomycetes, zygomycetes

Sexual reproduction in fungi:

• Sexual reproduction is carried out by diffusion of compatable nuclei from two parent at a definite state in the life cycle of fungi.
• The process of sexual reproduction involves three phases:
  • Plasmogamy: fusion of protoplasm
  • Karyogamy: fusion of nucleus
  • Meiosis: reductional nuclear division
• Various methods by which compatible nuclei are brought together in plasmogamy. Some are:
  • Gametic copulation
  • Gamete-gametangial copulation
  • Gametangial copulation
  • Somatic copulation
  • Spermatization

1. Gametic copulation:

• Fusion of two naked gametes, one or both of them are motile
  • Isogamous
  • Anisogamous
  • Oogamous

2. Gamete-gametangial copulation:

• Male and female gametangia comes into contact but do not fuse.
• A fertilization tube formed from where male gametangium enters the female gametangium and male gamate passes through this tube

3. Gametangial copulation;

• Two gametangia or their protoplast fuse and give rise to zygospore

 4. Somatic copulation:

• Also known as somatogamy.
• In this process fusion of somatic cell occurs
• This sexual fusion of undifferentiated vegetative cell results in dikaryotic hyphae, so the process is also called dikarotization

5. Spermetization:

• It is an union of special male structure called spertatium with a female receptive structure.
• Spermatium empties its content into receptive hyphae during plasmogamy

Sexual spores of fungi

• As a result of sexual reproduction sexual sores are produced.
• Sexual spores are fewer in number than asexual spores.

Types of sexual spores

i. Ascospore:

• It is usually single celled produced in a sac called ascus (plural;asci) and usually there are 4-8 ascospore in an ascus but the number may vary from species to species
• The ascospore are usually arranged in a linear order. In some case ascospores are long, narrow and are arranged in parallel order.

ii. Basidiospore:

• It is a reproductive spore produced by basidiomycetes.
• This single celled spores are born in a club shaped structure called basidium
• These basidiospore aerves as main air dispersal unit for the fungi.

iii. Zygospore:

• Zygospores are thick walled spores formed when two sexually compatible hyphae or gametangia of certain fungi fuse together.
• In suitable condition, zygospore germinates to produce a single vertical hyphae which forms a aporangium and releases its spores

iv. Oospore:

• These are formed within a special female structure called Oogonium.
• Fertilization of egg by male gamete in female sex organ give rise to oospoes.
• There are one or more oospores in each oogonium.

Reproduction in fungi: asexual and sexual methods