Venturia

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Venturia
Apple scab (Venturia inaequalis)

Apple scab ( Venturia inaequalis )

Systematics
Subdivision : Real ascent mushrooms (Pezizomycotina)
Class : Dothideomycetes
Subclass : Pleosporomycetidae
Order : Pleosporales
Family : Scab relatives (Venturiaceae)
Genre : Venturia
Scientific name
Venturia
Sacc.

Venturia is a genus of Ascomycetes (Ascomycota) from the order pleosporales . The fungi cause diseases in fruit and other deciduous trees called scabs .

features

Macroscopic features

The fruiting bodies are embedded in the host tissue and form a scaly appearance on the surface.

Microscopic features

The small fruiting bodies consist of perithecia-like pseudothecia , which can be developed individually or in groups, and which have a tiny, superficial, wart-shaped opening, the ostiolum. The ostiolum can rarely be provided with bristles. The cell walls of the fruiting body are made up of brown, thick-walled cells, the pseudoparenchyma , but the inner cell walls are hyaline and thin-walled. In the center of the fruiting body there are filamentous, branched and septate pseudoparaphyses . The asci are bitunicate , that is, two-layered, cylindrical or elongated, short-stalked and always with eight spores . These are elongated, elliptical, club-shaped or spindle-shaped from olive-green to pale or dark brown in color. They can be smooth or warty or slightly prickly, sometimes with a thin gelatinous coating. They are septate below or above the middle, sometimes a little constricted there.

Scanning electron microscope image of the spores of apple scab ( Venturia inaequalis ) breaking out of the tissue

The secondary crop forms are assigned to Fuscladium , Cladosporium , Pollaccia and Spilocaea . In Fusicladium , the mycelium is embedded and often has a stroma . The conidiophores are single or once branched and usually arranged in tufts. The conidia are solitary or in short chains and often spindle-shaped. They are 0-3x septate, pale to olive brown and fine black. In Cladosporium , the colonies are fluffy, flaky, and only sometimes with a stroma. The conidiophores are straight or curved, mostly unbranched. The conidia are arranged in chains, simple, cylindrical to oblong, but also spherical, often with a notch at the base. They are smooth, warty or prickly and 0-3x septate.

If the minor crop form is Pollaccia , irregularly distributed, sometimes confluent, sporodochia are formed. A stroma is formed in or under the epidermis . The conidiophores are simple, smooth, compressed, hyaline to olive green. The conidia are solitary, cylindrical or elliptical, obtuse at the base and rounded at the tip. They are hyaline or olive-colored, smooth or warty, 1-2x septate. As a fourth form, Spilocaea can be formed. Here the mycelium is in the tissue and forms round discs. There is usually a stroma. The conidiophores are usually simple, straight or curved, brown and smooth. The conidia are single, mostly pear-shaped to club-shaped. They are pale to olive brown, un- or simply septate, rarely more, sometimes constricted at the septum.

Ecology and importance

The species all live parasitically on living plant tissue , mostly on the leaves. Some species then form fruiting bodies on overwintered leaves.

Pear scab

Since several species are found on fruit trees, they are of particular economic importance. This is especially the Pfirsichschorf ( Venturia carpophila ), in addition to peaches and nectarines, apricots infests plums and almonds, the Kirschenschorf ( Venturia cerasi ), the apple scab ( Venturia inaequalis ) and the Birnenschorf ( Venturia pyrina ).

Spread and control

The fungi themselves overwinter on the fallen leaves as ascospores (winter spores), which are thrown up when it rains in the spring and, if the rain period is long enough, attack leaves or fruits, whereby they only penetrate the cuticle . The maximum of the spore flight often coincides with the flowering of the fruit crops. In summer, conidia (summer spores ) form on the infected areas .

The raking or raking of the fallen leaves and their professional composting serves to protect against excessive infestation. However, this measure can only be carried out in an allotment garden. Commercial cultivation continues to protect the trees through the application of pesticides based on a warning service (scab forecast) at a specific time. A biological fungicide suitable for the species of pome fruit is the bacterium Bacillus subtilis , strain QST 713.

Surname

The name honors the Italian bryologist Gustavo Venturi .

Taxonomy

Species of the genus Fusicladium are counted to Venturia , since the former form the secondary fruit form , the latter form the main fruit form. Some species of Cladosporium , Pollaccia and Spilocaea also form secondary crop forms of Venturia . The type species is Venturia inaequalis . The genus contains 57 species:

Individual evidence

  1. ^ A b c Richard T. Hanlin: Illustrated genera of Ascomycetes. Ed .: The American Phytopathological Society. tape 2 . APS Press, 1990, ISBN 978-0-89054-107-4 , pp. 164 ( accessed from mycobank on May 29, 2015 ).
  2. ↑ a b c d e A. Sivanesan: The Bitunicate Ascomycetes and their anamorphs. Lubrecht & Cramer Ltd, 1984, ISBN 978-3-7682-1329-5 , pp. 701 ( accessed from mycobank on May 29, 2015 ).
  3. ↑ a b Scab diseases. ( Memento of the original from September 3, 2013 in the Internet Archive ) Info: The @1@ 2Template: Webachiv / IABot / www.dega-galabau.de archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 263 kB) DEGA, 35/2004.
  4. ↑ Adalbert Griegel: My common orchard. Large disease and pest calendar. Griegel, 2001. p. 98.
  5. ^ Horst Börner: Plant diseases and plant protection. 8th edition. Springer, Heidelberg et al. 2009, ISBN 3-540-49067-1 . P. 442.
  6. ↑ BHL Taxonomic literature: a selective guide to botanical publications
  7. ↑ Andreas Beck, Anja Ritschel, Konstanze Schubert, Uwe Braun, Dagmar Triebel: Phylogenetic relationships of the anamorphic genus Fusicladium s. lat. as inferred by ITS nrDNA data. In: Mycological Progress . tape 4 , no. 2 , 2005, p. 111-116 , doi : 10.1007 / s11557-006-0114-8 .
  8. ↑ Kirk PM, Cannon PF, Minter DW, Stalpers JA .: Dictionary of the Fungi. 10th edition. CABI, Wallingford, UK 2008, ISBN 978-0-85199-826-8 , pp. 722 ( accessed from Google Books on May 29, 2015 ).

Web links

Commons : Venturia  - collection of images, videos and audio files