Filamentous Ascomycetes

Filamentous Ascomycetes

  1. Plectomycetes (Cleistothecial ascomycetes)

Characters:

  • Those Ascomycetes which have closed ascocarp are called Cleistothecial Ascomycetes or Plectomycetes.
  • Asci are thin walled, pyriform, globose and evanescent (delicate).
  • Asci are scattered at various levels within the ascocarp without forming a hymenium (a basal layer of asci).
  • Ascospores are unicellular.
  • Ascocarp is typically cleistothecial.
  • Various types of anamorphs or conidial forms are characteristics of various orders and families.
  • Members of this group produce powdery mildews in their hosts.
  • Powdery mildew is the superficial powdery mass of fungus on different plant parts.

 

 

Taxonomic Status

Taxonomic category

Genus/ species

Disease caused

Order: Erysiphales

Family: Erysiphaceae

Erysiphe graminis     

 

E. cicharacearum                  

E. polygoni                

 

Phylactinia dalbergiae           

Podosphaera leucotricha                       

Uncinula nector        

Powdery mildews in cereals 

 

 

Powdery mildews of cucurbits

 

 

Powdery mildews of peas

 

 

Powdery mildews of shishum

 

 

Powdery mildews of Apples

 

 

Powdery mildews of grapes

Order: Eurotiales

Family: Trichocomaceae

 

 

Eurotium sp

 

 

 

 

Filamentous Ascomycetes

 

  1. Pyrenomycetes (Perithecial Ascomycetes)

Characters:

  • Asci are present in the form of Hymenium.
  • Asci are persistant.
  • Perithecial ascocarp is present.
  • Asci are within an apical pore.
  • Ascospores are spherical to needle shaped.
  • These are important as parasites and symbionts of Arthropods.
  • These are Endophytes of a variety of living plants e.g. plants of family Gramineae.
  • Endophytes are those parasites, which penetrate into the host body.
  • These are mycotoxin producers, mammalian parasites, plant parasites, on saprophytic particularly on lignocellulosic (lignin+cellulose) substrates.
  • Mycotoxins are the poisonous compounds produced by the fungi.
  • For example Fusarium penetrates into xylem of their plant host and produces different toxins, which contribute in the wilting of plants.
  • Plant pathogenic Pyrenomycetes produce toxins that may kill a plant or a part of plant.
  • Now a day these plant pathogenic fungi are being used as mycoherbicides to control the weeds.
  • Some members are mycoparasites belong to order Hypocreales.
  • Hyper parasitism: It is the growth of one parasite on another parasite.
  • Trichoderma and Gliocladium are used to control soil born fungi.
  • Some members produce mycotoxins in stored grains and cause adverse effect in mammals’ e.g. Claviceps purpurea that causes Ergot disease in rye, produces a toxin Ergotamine that causes abortion in mammals.
  • Some members are intimately associated with arthropods especially the insects.

 

Taxonomic Status

Taxonomic category

Genus/ species

Disease caused

Order: Hypocreales

Family: Clavicipitaceae

 

Claviceps purpurea

           

Ergot of rye

Order: Xylariales

Family: Xylariaceae

 

 

 Xylaria sp.

 

 

Order: Sordariales

Family: Sordariaceae

 

Sordoria sp.

Neurospora sp

 

 

 

Filamentous Ascomycetes

  1. Discomycetes (Apothecial Ascomycetes)

Characteristics:

  • Ascocarp is Apothecium.
  • They are Epigean as well as Hypogean.
  • Discomycetes are characterized by colourful ascocarp, which is of often cup shaped structure.
  • Ascospores are discharged forcibly from cylindrical to ovoid (oval shaped) asci.
  • Many members are saprobes on lignocellulosic substrate
  • Some of them appear on substrate after they may have burnt on or soaked with urine.
  • Morels and truffles are included in this group.
  • These have been divided into three groups:
  1. Operculate Discomycetes
  2. Inoperculate Discomycetes
  3. Lichen Forming Discomycetes
  1. Operculate Discomycetes: These have completely closed hypogenous ascocarp. Ascospores have passive spore discharge but a few species produce forcibly discharged asci.
  2. Inoperculate Discomycetes: These produce forcibly discharged ascospores.
  3. Lichen Forming Discomycetes: Lichen is the association of fungus and algae or cyanobacterium in which organisms are intertwined to form a single thallus.

Structure of ascocarp:

            The structure of apothecium consists of Hymenium, Hypothecium, and Exicipulum.

  • Hymenium: It is a cup shaped structure made up of cylindrical asci usually with Paraphyses.
  • Hypothecium: It is a thin layer of interwoven hyphae located immediately below the hymenium.
  • Exicipulum: The flashy part of ascocarp that supports the hypothecium and hymenium is known as exicipulum.

Asci of Discomycetes are of two types:

  1. Operculate asci
  2. Inoperculate asci
  1. Operculate Asci: A lid like structure known as operculum opens and allows the escape of ascospore.
  2. Inoperculate Asci: In inoperculate asci, spores are released through a rough, an apical, circular opening or perforation.

 

 

Taxonomic Status

Taxonomic category

Genus/ species

Disease caused

Order: Helotiales

Family: Sclerotiniaceae

 

 

 

Monilinia fructicola 

Monilinia fructicola (brown rot) is a costly cause of disease in stonefruit.Brown rot of Stone Fruit Brown rot of Stone Fruit

 

 

 

 

Filamentous Ascomycetes

  1. Loculoascomycetes (Pseudothecial Ascomycetes)

Characters:

  • Ascocarp is Pseudothecial and is stalked.
  • These are characterized by the production of asci within locules in a preformed stroma (i.e. Ascostroma) that constitute the ascocarp.
  • Ascus is bitunicate with two separable wall layers.
  • Pseudothecium usually develop an ostiole lined with periphyses.
  • Globose asci occur singly in locules that are scattered or grouped in fertile regions of stromatal tissue.

 

 

 

 

Taxonomic Status

Taxonomic category

Genus/ species

Disease caused

Order: Pleosporales

Family: Venturiaceae

 

Venturia inaequalis           

apple scab, caused by Venturia inaequalis-- photo by Debby Hanmer of UW-La CrosseApple scab

 

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