Phylum Ascomycota, its brief characters, Generalized life of ascomycetes, sexual and asexual fruiting bodies.

PHYLUM ASCOMYCOTA

 

CHARACTERISTICSS:

  1. Member of Ascomycota and Basidiomycota are called higher fungi.
  2. Sac like structure is produced which is known as ascus.
  3. Within ascus (Pl. asci) spores known as ascospores are produced, which are usually eight (8) in numbers?
  4. This group consists of 1500 species and includes ascus forming yeasts, black and green molds, powdery mildews, cup fungi, morels and truffles.
  5. Hyphae or mycelium is well developed with distinct walls which are made up of chitin.
  6. Hyphae are septate and septa of the hyphae have a simple pore and woronin bodies are present.
  7. Woronin bodies are spherical, hexagonal or rectangular structures that are usually associated with a septum and can only be visible with an electron microscope.
  8. There is a free cell formation after karyogamy and meiosis.
  9. Types of Ascocarp: In ascomycetes the wall appears two layered, with a thick, translucent inner layer (endotunica) and a dense, thin outer layer (exotunica).

There are three types of ascocarp on the basis of these layers.

  1. Prototunicate: It has only single layer, which is delicate, and there is no opening. OR When the ascus is covered by thin and delicate membrane. Ascospores are released by breaking of thin and delicate wall of ascus.

 

  1. Unitunicate: The two layers are so arranged that they are fused and difficult to distinguish. OR If the inner and outer walls are more or less rigid and do not break during spore dispersal.

 

  1. Bitunicate: The two layers are quite separate and easily distinguished. OR If the inner wall is elastic enough than the outer wall and expand enough during spores dispersal.
  1. The somatic phase of ascomycetes may be single-celled, mycelial or dimorphic.

 

Fruiting body of ascomycetes in which asci are produced is called Ascocarp [ (syn. ascoma) sexual fruiting body of an ascomycetous fungus that produces asci and ascospores; e.g. apothecium, ascostroma, cleistothecium, perithecium, pseudothecium].

 

  1. Asexual reproduction may be carried out by fission, fragmentation, budding or formation of chlamydospores [thick-walled or double-walled asexual resting spore formed from hyphal cells (terminal or intercalary) or by transformation of conidial cells that can function as an overwintering stage]
  2. Sexual reproduction is by gametangial contact, by somatogamy and spermatization.
  3. Heterothallic fungi may be unifactorial (bipolar) or bifactorial (tetra polar).
  4. Concentric bodies are present in the lichen forming ascomycetes.
  5. A definite layer of asci, whether naked or enclosed in an ascocarp, is called a Hymenium [continuous, spore-bearing layer of a fungus fruiting body (hymenium of asci on the surface of an apothecium of Monilinia fructicola)].

HABITAT:                                                                                      

These occur in a variety of habitats.

  1. Coprophilous fungi that live in dung habitats denote the specific fungi living in  
  2. Corticolous fungi in / on bark
  3. lignicolous fungi on/ in wood 
  4. folicolous fungi on  leaves
  5. hypgean, developing and remaining under ground.

IMPORTANCE:

  • Like the yeast these are also used in baking and brewing industry.
  • Production of antibiotics.
  • Production of organic acids.
  • A number of them are used as food such as mushrooms, morels and truffles.
  • These cause a large number of diseases.

NUTRITION:

            Nutritionally these are saprophytes, parasites and lichen forming.

Parasexual Lifecycle: In ascomycetes the Plasmogamy [the fusion of two sex cells], karyogamy [the fusion of nuclei] and meiosis do take place but do not at specific time. This type life cycle is called parasexual life cycle. It was proposed by Pontecorvo in 1956.

Deuteromycetes

(Asexual Ascomycetes and other Asexual Fungi)

These are also referred as Fungi Imperfecti or Conidial Fungi.

Those ascomycetes and basidiomycetes that can never reproduce sexually are called deuteromycetes.

 

Taxonomic Status

Taxonomic category

Genus/ species

Disease caused

Order: Sphaeropsidales

Family: Sphaeropsidaceae

Ascochyta rabie

 Gram blight

Order: Melanconiales

Family: Melanconiaceae

Colletotrichum falcatum

C.. gloeosporioides

Red rot of sugarcane

Antharcanse of citrus

Order: Moniliales

Family: Moniliaceae

Aspergillus niger                        

Penicillium expansum

 Soft rot of fruits 

Soft rot of vegetables

Order: Moniliales

Family: Dematiaceae

Alternaria solani

Cercospora personate

Early blight of potato

Tikka disease of groundnut

Order: Moniliales

Family: Tuberculariaceae

 

Helminthosporium oryzae

Pyricularia oryzae

 

Fusarium oxysporum f.sp. ciceris

Leaf spot of rice Rice blast

 

 

Gram wilt

Order: Ogonomycetales

 

Rhizoctonia solani

Root rot of cotton

 

 

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