White rot
The process of lignin degradation in woody plants by fungi is called white rot (also known as corrosion rot ) . This type of wood rot can only be found among the mushrooms of the class Agaricomycetes . White rot is the only known way that organisms break down lignin and related compounds for use in their metabolism . Macroscopic symptoms of white rot are primarily the white color of the affected wood, its fraying and the associated loss of stability. The physiological foundations necessary for white rot - including the production of the enzyme laccase - probably appeared for the first time towards the end of the Carboniferous period (around 300 million years ago). At the same time, the deposition of lignin in the form of today's hard coal decreased significantly. The emergence of white rot is therefore seen as a cause for this decline. From the wood industry's point of view, white rot fungi are pests because they damage trees suitable for logging and can devalue wood that has already been extracted.
Course and symptoms
The destruction of wood can already occur on a living trunk, especially on hardwood. White rot fungi are able to break down cellulose , hemicellulose and lignin . A distinction is made between selective (successive) and simultaneous degradation. In the case of selective white rot, lignin (and hemicellulose) are initially broken down more strongly than cellulose. This makes the wood look more light / white. Simultaneous white rot is characterized by the simultaneous breakdown of all three cell wall components, which makes the wood appear darker. In contrast to white rot, brown rot fungi mainly destroy the cellulose content.
In the case of a white rot disease, the wood structure remains largely intact, but the wood becomes lighter, lighter, more fibrous and foxy. A uniform whitish-gray discoloration develops, the wood loses its luster. Characteristic are dark lines that separate the infected from the healthy parts. These so-called demarcation lines allow the fungus to regulate the moisture in the wood. In the final stage, the wood is "spongy", often with marble-like stripes.
According to EN 335: 2013 "Durability of wood and wood products", a wood moisture content of more than 20% is usually required for the development of fungi. In addition to living trees, white rot is also found in storage wood. In buildings, white rot can occur, for example, in the area of damaged roofs or sanitary facilities. Trunks infested with white rot can no longer be used as construction timber.
Special forms of white rot
A special form of white rot is white-hole rot or honeycomb rot . It causes the lignin to break down unevenly and occurs mainly in the core of living conifers and deciduous trees. White hole rot is caused by the pine fire sponge ( Phellinus pini ) and the common mosaic layer fungus ( Xylobolus frustulatus ). The white hole rot can be recognized by the small, often lens-shaped and initially filled with white fiber remnants, later mostly empty, hole-like cavities.
Evolution and pathogens
White rot as a metabolic type occurs exclusively in fungi of the class Agaricomycetes . The basal group, which is able to do this, are the ear flap fungus-like (auriculariales). White rot occurs in both basal and derivative groups of the class, but these clades are not necessarily closest relatives. Rather, white rot is an original feature of the Agaricomycetes, which has been retained by some side branches and largely abandoned by others in favor of brown rot or mycorrhizal formation . It probably first appeared around 300 million years ago. It allowed the ancestor of today's Agaricomycetes to use lignin as a resource and thus claim a previously unoccupied niche for themselves.
New studies suggest a connection between the formation of thick coal seams and the evolution of white rot. In the Carboniferous there were no living creatures could degrade lignin. It was not until the Tertiary that white rot fungi developed, which decomposed lignin. After that, coal could only form in the absence of air.
Among the fungal groups engaged in white rot, include not only the ear flap mushroom-like (Auriculariales) the bristle Scheibling-like (Hymenochaetales), the splendor beef Fungus (Corticiales), various branches of Stielporlingsartigen (Polyporales) that Täublingsartigen (Russulales) and some representatives of the mushroom-like (Agaricales).
literature
- Heinz Butin : Diseases of the forest and park trees. Diagnosis, biology, control. 2 spore boards . 3rd, revised and expanded edition. Thieme, Stuttgart and New York 1996, ISBN 3-13-639003-2
- Tobias Huckfeldt, Olaf Schmidt: House rot and timber fungi. Verlag Rudolf Müller, Cologne 2006, ISBN 3-481-02142-9 , 377 pp.
- Hermann Jahn: Fungi on trees Patzer Verlag, Berlin-Hanover, ISBN 3-87617-111-3
Web links
Individual evidence
- ↑ a b c d Dimitrios Floudas, Manfred Binder, Robert Riley, Kerrie Barry, Robert A. Blanchette, Bernard Henrissat, Angel T. Martínez, Robert Otillar, Joseph W. Spatafora, Jagjit S. Yadav, Andrea Aerts, Isabelle Benoit, Alex Boyd, Alexis Carlson, Alex Copeland, Pedro M. Coutinho, Ronald P. de Vries, Patricia Ferreira, Keisha Findley, Brian Foster, Jill Gaskell, Dylan Glotzer, Paweł Górecki, Joseph Heitman, Cedar Hesse, Chiaki Hori, Kiyohiko Igarashi, Joel A. Jurgens, Nathan Kallen, Phil Kersten, Annegret Kohler, Ursula Kües, TK Arun Kumar, Alan Kuo, Kurt LaButti, Luis F. Larrondo, Erika Lindquist, Albee Ling, Vincent Lombard, Susan Lucas, Taina Lundell, Rachael Martin, David J. McLaughlin, Ingo Morgenstern, Emanuelle Morin, Claude Murat, Laszlo G. Nagy, Matt Nolan, Robin A. Ohm, Aleksandrina Patyshakuliyeva, Antonis Rokas, Francisco J. Ruiz-Dueñas, Grzegorz Sabat, Asaf Salamov, Masahiro Samejima, Jeremy Schmutz , Jason C. Slot, Franz St. John, Jan Stenlid, Hui Sun, Sheng Sun, Khajamohiddi n Syed, Adrian Tsang, Ad Wiebenga, Darcy Young, Antonio Pisabarro, Daniel C. Eastwood, Francis Martin, Dan Cullen, Igor V. Grigoriev, David S. Hibbett: The Paleozoic Origin of Enzymatic Lignin Decomposition Reconstructed from 31 Fungal Genomes . In: Science . 336, No. 6089, June 2012, pp. 1715-1719. doi : 10.1126 / science.1221748 . Retrieved March 29, 2013.
- ^ Peter Schütt, Hans J. Schuck & Bernd Stimm: Lexicon of tree and shrub species . The standard work of forest botany. Morphology, pathology, ecology and systematics of important tree and shrub species. 3. Edition. Nikol Verlag, 2011, ISBN 978-3-86820-123-9 .