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FUNGAL BIOLOGY
A Textbook by JIM DEACON
Blackwell Publishing 2005

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BASIDIOMYCOTA: "FAIRY RING" FUNGI OF GRASSLANDS

Several common decomposer fungi grow on the accumulated "thatch" of dead roots and basal stem tissues in natural or amenity grasslands, including sports turf. The most common of these fungi are the Hygrocybe species, commonly known as "wax caps" because of their waxy texture and appearance. Many of them produce strikingly coloured fruitbodies. These fungi cause no significant damage to the grass turf, and often the only visible symptom of their presence is a slowly expanding ring of turf that is lusher and deeper green. This results from the breakdown of dead organic matter, releasing nitogenous nutrients that locally stimulate growth of the turf.

There are more than 200 species of wax caps, including more than 50 in Britain. The examples shown below have caps about 3-4 cm diameter.


Fruitbodies of a Hygrocybe species in a natural pasture (possibly H. coccinea, although there are several similar species of red wax caps).
[ Jim Deacon]


Left: the Conical Wax Cap (Hygrocybe conica), growing among pasture grasses and mosses in a heathland environment. The initial yellow colour of the stipe of this species rapidly turns black when bruised. Right: Basidiocarps of one of the yellow-coloured Hygrocybe species, probably H. langei, growing in short upland grassland. [ Jim Deacon]

In contrast to the Hygrocybe spp, which cause little or no damage to grassland, the common fungus Marasmius oreades (" Fairy Ring Champignon") can cause significant damage to grass turf and adversely affect the playing qualities of sports turf. Again, this fungus grows on the accumulated thatch of dead turf, and spreads progressively outwards as a ring. But it can locally kill the turf as it spreads progressively into new zones of turf (see the images below). There has been speculation that this fungus might kill the turf by producing toxins, but this has never been substantiated. Instead, the killing zone is likely to be caused by the mass of Marasmius hyphae just below the soil surface. These hyphae are strongly hydrophobic (repelling water) and so they can prevent the turf from absorbing water, leading to grass death. In fact, one of the best ways of preventing the turf from dying is to apply a surfactant, such as diluted washing-up liquid.


Marasmius oreades, the "fairy ring champignon" that can cause killing zones in grass turf. Two fruitbodies, with caps about 3cm wide, have been pulled up. Note the characteristic pattern of the gills - some are short and some are long, but they do not run down the stem.[ Jim Deacon]


A ring of grass death, caused by Marasmius oreades. Just visible in this image is a ring of slightly greener, lusher grass growth immediately inside the dead zone. This is caused by the release of nutrients (nitrogen, phosphorus, etc.) from the killed zone of turf. [ Jim Deacon]


An area of turf lifted with a spade within the dead zone of a fairy ring caused by M. oreades, showing the profusion of fungal hyphae immediately below the surface of the turf. The hyphae are strongly hydrophobic, so they prevent water from penetrating into the soil, leading to death of the turf. [ Jim Deacon]

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