The fungus Ganoderma applanatum, whose some other names are Fomes applanatus and Polyporus applanatus, is a very important organism. In fact, it causes some damages that can be lethal for trees, and it affects a lot of different species. It belongs to heart rot fungus that means that it provokes a destructuring of wood, inside the stem, and even inside roots.

So, it decreases the value of a stand, as timber can not be sold, and trees that survive to this disease are very weak against wind or other environmental factors. For example, they can be attacked by other pathogens. Besides, we can find a lot of windthrows on infested stands.

The main problem of this pathogen is that it attacks a lot of species, from different genus. It affects essentially hardwood, but many conifers are susceptible to this fungus too. So, even in mixed stand, it seems to be difficult to prevent the spread of this kind of fungus.

For example, concerning hardwood, we can find some decays on the following genus : Acer, Alnus, Betula, Fagus, Populus, Quercus, Salix, Ulmus... So, we can see that it touches the majority of species that we can find in France. It shows the importance of this fungus. Even if consequences are not dramatic for the moment, we have to be aware of the risk that it represents.

Moreover, it attacks some softwood species, even if it is not in the main cases. Concerning conifers, we can find the fungus for example on Abies, Picea, Pinus, Pseudotsuga, Thuja, Tsuga genus. Species like Scots pine, Norway spruce or even Douglas-fir are too important to allow the spread of this heart rot fungus.

This disease is really common in the Northern hemisphere, either in North America or in Europe. So, its distribution is not limited to a region. In Canada, in the USA... it is scattered in the whole territories. In Europe, we can find it in France, or even in Great-Britain.

It is due to the adaptability of this fungus, which is not restricted to attack one genus. Because of it, only good conditions of development are required by this organism to grow well.

However, it seems to be more dangerous and harmful in mountains regions. So, even at high altitudes, the fungus is present and relevant. It also increases the distribution.

This disease is caused by heart decay. It has a fungal origin, whose spread is now global in our hemisphere. Some Ganoderma species are even studied in Indonesia, as we can find it there.

This fungus belongs to the Order of Aphyllophorales and belongs to the family of Basidiomycota.

Spores can colonize a tree, by entering trough the wounds. That is why it is important to prevent them. Once it is inside, it can begin to develop, and infest the tree. Carpophores will only appear a few years after the beginning of infection. During the different phases of infection, wood will become white, while it will be encircled by a dark brown stain. At the end, once wood is totally white, it also becomes spongy and weak.

Like every fungus, the scattering can be fast and efficient because of the wind. Spores are tiny and light, so that it can be brought many kilometres away, even in the lightest winds. Besides, along a littoral, spores that are free can be transported by water. It shows that it can travel for a long time and a long distance, before finding good conditions to develop. Spores are resistant to exterior factors as they are in a dormant stage. It permits them to wait good conditions.

Moreover, it is said that this fungus can produce 350000 spores per second, which is very huge. So, great epidemics could happen, if we do not act.

This fungus is quite easy to recognize, and its presence is always noticeable. In fact, the first sign that has to be observed is presence of windthrows. Indeed, as heartwood is rotten and destructed by such a fungus, trees become weak and can fall because of the wind. Some infected trees are still alive and standing up. However, we can see that the size of leaves is lesser, which means that the production will not be optimum.

Furthermore, like a lot of heart-rot fungi, some big carpophores occur on the trunk. They are the fruiting bodies of the fungus, and they are often based on the basis of the bole, near root systems. These carpophores are flat and two different colours can be seen : white on the underside of the fungus, while the upper side is brown. However, the underside darkens with the age.

On timber, we can observe a white rot, caused by the fungus. It means that lignin and cellulose are not in cells anymore, therefore timber becomes very weak.

Preventive control is quite impossible. In fact, even if we try to prevent appearance and spread, it is not efficient enough. We saw that too many species were susceptible, so, in plantations, it is difficult to select a resistant species.

After infection, ways of fighting the fungus are quite common with other diseases. However, it is not really efficient to fight directly the pathogen. We have to prevent the spread, as no curative treatment can be applied, but once a tree is infected, it is not possible to cure it. In fact, the main thing to do is to remove infested trees. We can see the infection with carpophores, which appear several years after infection. Besides, dead trees are not always on the ground, which means that there are some dead trees that are standing up. These ones are the most dangerous and must be identified and cut.

By the way, during a harvesting, we have to limit wounds. Some trees can obviously be damaged during this operation. But, wounds are the places where a fungus can penetrate a tree. Therefore, when there is a wound, we recover it by fungicide mastic.

This fungus is well-known because we can find it almost everywhere. So, a lot of scientists are used to working on it to discover how it works. In fact, the main progress would be to find a resistant species.

Indeed, plantations are quite difficult because a lot of species that are normally planted are susceptible to this pathogen. So, we must discover species that are not sensitive at all, so that we will be sure to limit the spread of the disease.

•http://www.bluewillowpages.com/mushroomexpert/ganoderma_applanatum.html

•http://www.pfc.forestry.ca/diseases/CTD/Group/Heart/heart6_e.html

• Tree Doctor Software, developed by CFPF, French Agriculture and fishing Minister, Chlorophyl Assistance, Citare, French forest development Institute, Disease and advisory Service forest research, Instituto per le piante de legno e l’ambiente, Alterra, Staatsbosehner, IPC groene ruimte