Ascomycetes : The sac fungi
- The mycelium consists of septate hyphae (Yeasts are an exception in that they are basically unicellular).
- They are saprophytic, decomposers, parasitic or coprophilous (growing on dung).
- The septa possess central pores called septal pores. The pores allow communication and transport between adjacent cells.
- Cell wall contain chitin.
- Motile structures do not occur in the life cycle.
- In majority of ascomycetes. The common mode of asexual reproduction is through the formation of conidia. Conidia are borne on branched or unbranched hyphae called conidiophores, e.g., Penicillium Aspergillus.
- Female sex organ is called ascogonium.
8.Plasmongamy occurs by means of –
- i) Gametangial contact (e.g., Pyronema) ii) Conjugation ( e.g., Yeast) (iii) Spermatization (e.g., Ascobolus) iv) Somatogamy (e.g., Peziza) v) Autogamy (e.g., Morchella).
- Karyogamy is delayed after plasmongamy. A new transitional phase appears in the life cycle. It is called dikaryophase. The cells of dikaryophase are called dikaryotic cells. Each such cell possesses two different nuclei (Dikaryon). This forms a shorter phase of life cycle.
- Once a cell becomes dikaryotic, it transfers the nucleus to other cells by the crozier method (method of dikaryotization ) to make them dikaryotic.
- Some dikaryotic cells function as ascus mother cells. This converts the cells into asci (singular- ascus). Ascus is a sporangial sac peculiar to Ascomycetes. Ascus is the site of karyogamy and meiosis. 4 to 8 haploid meiospores named ascospores are produced endogenously in each ascus. In most of the cases, half the number of ascospores belong to one mating type (+) while the other half belong to the second mating type (-).
- Ascopores may be arranged linearly (Neurospora) or unorderly (yeast).
- The asci may occur freely or get aggregated into specific fructifications called ascocarps. Ascocarps are of many types ; cup-like (apothecium, e.g., Peziza) flask – shaped (perithecium , e.g., Neurospora, Claviceps) , elongated with a slit (hysterothecium), cloased cleistothecium , e.g., Penicillium ) cushion like , chambered ( Ascostroma, e.g., Pleospora ). The fructifications of some ascomycetes are edible, e.g., morels, truffles.