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Phylum Ascomycota Orders Erysiphales & Laboulbeniales. General Mycology Pl P 421/521 Lecture 7. Pyrenomycetes. Plectomycetes (Eurotiales). Chaetothyriales. Loculoascomycetes 1. Loculoascomycetes 2. Filamentous ascomycetes. Inoperculate discomycetes. Lecanoralean discomycetes.

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Phylum ascomycota orders erysiphales laboulbeniales l.jpg

Phylum AscomycotaOrders Erysiphales & Laboulbeniales

General Mycology

Pl P 421/521

Lecture 7


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Pyrenomycetes

Plectomycetes (Eurotiales)

Chaetothyriales

Loculoascomycetes 1

Loculoascomycetes 2

Filamentous ascomycetes

Inoperculate discomycetes

Lecanoralean discomycetes

Operculate discomycetes

Erysiphales (powdery mildews)

Laboulbeniales

Saccharomycetales

Archiascomycetes

Basidiomycota




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Erysiphales

  • Common name = Powdery Mildews

  • Biotrophs of vascular plants

    • Biotroph: an obligate parasite growing on another living organism

  • 21 genera, 437 species infecting > 40,000 species of plants (mostly dicots)

  • Most species are host specific, a few are omnivorous, infecting hundreds of host species


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Powdery Mildew Symptoms

Photo by Claudia Nitschwitz


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Characteristics

  • Mycelium is mostly superficial

    • Anchored to host epidermis by appressoria

  • Nutrients obtained via haustoria

    • Haustoria are intracellular structures

  • Overwinter as mycelium in infected buds or as ascomata

  • Asexual reproduction via conidia

  • Sexual reproduction via ascospores formed in cleistothecia



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appressorium

Plasma membrane

Penetration peg

haustorium

Host cytoplasm

Plasma membrane

Plant cell wall

fungus


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Asexual reproduction

  • Erect, hyaline conidiophores are usually formed on superficial mycelium;

  • One-celled, hyaline thin-walled conidia are produced holoblastically in basipetal chains

  • One colony can produce > 30,000 conidia


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Conidia

  • Wind-dispersed

  • Germination can occur at low relative humidity

  • Germination involves germ tube, appressorium and penetration peg formation

  • Apex of penetration peg enlarges to form haustorium


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Ovulariopsis

Oidium type anamorph

Oidiopsis

Streptopodium

Fibrosin bodies

From Braun, 1987


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Microsphaera alni anamorph on Vaccinium


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Sexual reproduction

  • Cleistothecia formed on superficial mycelium in late summer/early fall

  • Asci

    • Formed in basal layer

    • Globose to pyriform

    • Discharge by rupture of ascus tip


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Asci/Ascospores

  • One to numerous asci/cleistothecium

  • Ascospores hyaline, one-celled, ovoid

  • 1-8 ascospores/ascus

  • Number of asci/cleistothecium is important character in identification



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Identification

  • Anamorph type

  • Number of asci/ascocarp

  • Cleistothecial appendages

    • Mycelioid

    • Rigid

      • Spear-like with inflated base

      • With curled tips

      • With dichotomously branched tips


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Microsphaera alni cleistothecia


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Sawadaea bicornis cleistothecia


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Sawadaea bicornis cleistothecial appendages


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Blumeria

  • B. graminis--only powdery mildew on grasses

  • Mycelial setae

  • Digitate haustoria

  • Several asci/ascocarp

  • Inflated base on conidiophore


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Mycelioid Appendages

  • Several asci/ascocarp:

    • Eryisiphe (100 spp)

      • Oidium anamorph

    • Leveillula (8 spp.)

      • Internal mycelium

      • Oidiopsis anamorph (emerges through stomate)

  • One ascus/ascocarp:

    • Sphaerotheca (50 spp.)

      • Appendages with curled tips

      • Oidium anamorph with fibrosin bodies


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Dichotomously branched appendage tips

  • One ascus/ascocarp:

    • Podosphaera (12 spp.)

      • Oidium anamorph with fibrosin bodies

  • Several asci/ascocarp:

    • Microsphaera (125 spp.)

      • Oidium anamorph

    • Sawadaea (6 spp.)

      • Curved tips on appendages

      • Oidium anamorph with fibrosin bodies


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Spear-like appendages--Phyllactinia

  • 24 species

  • Appendages lift ascocarp off leaf surface

  • Brush cells on top of ascocarp

  • Ovulariopsis and Streptopodium anamorphs


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Appendages with curled tips

  • Uncinula (81 spp)

    • Oidium anamorph

    • Several asci/ascocarp

  • Uncinuliella

    • Differs by bristle-like appendages on top of ascocarp


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Molecular data vs. morphology

  • Phylogeny analyses of powdery mildews based on rDNA sequence data shows lineages corresponding to anamorph type rather than teleomorph morphology (Saenz & Taylor 1999, Can. J. Botany 77:150-168; Mori et al 2000, Mycologia 92:74-93)



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Class Laboulbeniomycetes

  • Orders Laboulbeniales and Pyxidiophorales

    • 5 families, 140 genera, > 1800 species

    • Members of 4/5 families lack hyphae, reduced to thallus attached to host

  • Parasitize arthropods


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Laboulbeniomycetes

  • Most species are highly host specific, found on only one arthropod species

  • Roland Thaxter (1858-1932) at Farlow Herbarium, Harvard was one of the leading experts on this group

    • Published a series of monographs on Laboulbeniales (1896-1931)



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Laboul images by Alex Weir Laboulbeniaceae"


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Hosts of Laboulbeniales (From Meredith Blackwell) Laboulbeniaceae"

Most species of. Laboulbeniales have been reported from beetles and flies in temperate regions, but recent studies in the tropics indicate that diversity in these regions may be much greater than in temperate areas, primarily because diversity of hosts, especially beetles, is much higher.


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Pyxidiophorales Laboulbeniaceae"

  • 2 genera, 16 species

  • Specialized for dispersal by arthropods (bark & dung beetles, phoretic mites)

  • Perithecia with ascospores that undergo extreme morphological changes during maturation


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Blackwell et al. 1986. Hyperphoretic dispersal of a Laboulbeniaceae"Pyxidiophora anamorph. Science 232: 993-995


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Pyxidiophora Laboulbeniaceae"perithecia

Development of anamorph

Photos by M. Blackwell


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Presumptive anamorph (above) Laboulbeniaceae"

From Kirschner (2003). Mycological Progress 2: 209-218.


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