ASCOMYCOTINA

Subkingdom: Mycota
Division: Eumycota
Sub-division: Ascomycotina

  • It is the largest group of fungi having more than 32,000 species in 3,400 genera
  • it is also known as Sac- Fungi
  •  askos – bag or bladder and mykes – fungus
  • It is characterized by the formation of an ascus
  • This consists of molds that have septated hyphae and some yeasts

Ascomycotina ASCOMYCOTINA| Sub- Division III

General Characteristics

  •  The spore formed by these fungi is known as ascospores which are sexually produced and are present within a sac
  • They consist of both parasitic and saprophytic species
  • They may be symbiotic
  • The majority species are terrestrial but few are aquatic ie. marine and freshwater
  • It is responsible for a few diseases like powdery mildew.
  • They show both sexual and asexual reproduction.
  • They produce the sexual ascospores and asexual conidiospores

Thallus Structure

  • It may grow either as yeasts, i.e. unicells multiplying by budding or fission or as mycelia which consist of septate hyphae
  • Mycelium is well developed with branched and septate hyphae
  • Mycelium may be homokaryotic  or heterokaryotic
  • Some fungi may be dimorphic ie. they can switch from the yeast to the filamentous state or vice versa. Ex- Candida

Classification

It is subdivided into 6 classes-

  1. Hemiascomycetes- Mycelium is poorly developed or absent, No ascocarp formation
  2. Plectomycetes- Mycelium is well developed, branched and septate, Ascocarp is formed
  3. Pyrenomycetes- Mycelium well developed and septate, ascocarp are produced
  4. Discomycetes- Well developed mycelium, Sex organs are lacking
  5. Laboulbeniomycetes- Thallus is reduced, Ascocarp is formed
  6. Loculoascomycetes- Thallus is mycelial, Ascocarp is formed

Ascomycetes Examples

  1. Saccharomyces
  2. Xylaria
  3. Peziza
  4. Phyllachora

Reproduction

Reproduction may occur sexually or asexually.

Asexual Reproduction

1. By Formation of Conidia-

  • These are exogenous and non-motile spores which are produced on the tip of conidiophores. They may be branched or unbranched  and unicellular or multicellular
  • Conidiogenesis occurs in two ways which appear to be distinct: blastic and thallic
  • Blastic– The conidium develops by the blowing-out of the wall of a cell, mostly from the tip of a hypha
  • Thallic- This occurs by conversion of a pre-existing hyphal element in which terminal or intercalary cells of a hypha become cut off by septa.

2. Other spore formations like Oidia or Chlamydospores- This may occur in some species.

Sexual Reproduction

Ascomycota have male and female gametangia in their haploid stage ie. antheridium and ascogonium respectively.

  1. Gametangial copulation
  2. Gametangial contact
  3. Plasmogamy– A single cell with two haploid nuclei. This creates a binucleate, dikaryotic condition in the ascogonium leading to karyogamy
  4. karyogamy– At the tip of the hyphae the nuclear fusion takes place

Diploid nucleus immediately undergoes meiosis followed by mitosis resulting in 8 haploid nuclei. Each nuclei accumulate cytoplasm, secrete a wall around it develop into an ascospore.

Life cycle

Ascomycotina

Economic Importance

  • The species Neurospora crassa has been the subject of intensive genetical research
  • Alcoholic fermentation by yeasts as the basis of the wine and brewing industries
  • Antibacterial antibiotics such as penicillin from Penicillium chrysogenum and cephalosporin from Acremonium spp.
  • Food production as in bread-making by yeast, cheese ripening by Penicillium roqueforti and P. camemberti
  • Food spoilage may result from ascomycete contamination. ex- Claviceps purpurea

Reference

  1. Introduction to Fungi, Third Edition
  2. https://link.springer.com/chapter/10.1007%2F978-94-011-1496-7_4

More Topics To Read

  1. CLASSIFICATION OF FUNGI
  2. Mastigomycotina: Classification, Characteristics and Reproduction
  3. Zygomycotina: Classification, Characteristics and Reproduction
  4. Basidomycotina: Classification, Characteristics and Reproduction
  5. Deuteromycotina: Classification, Characteristics and Reproduction