Maples destroy bark disease. The fungus is also dangerous to humans.

However, over the past 20 years, the fungus has spread throughout almost all of Europe. It is believed that climate change is to blame, since the disease is especially common in hot and dry summers.

Scientists from the Institute for Forest Protection and Hunting of the Faculty of Forestry and Woodworking at the University of Mendel, together with European colleagues, used pollen monitoring samples and identified the movement of pathogen spores across Europe. Spores can spread through the air for hundreds of kilometers and can be dangerous to humans.

The fungus that causes sooty maple bark disease thrives best in dry months with no rainfall and average temperatures around 25 degrees Celsius, according to Milon Dvorak of the Forest Conservation and Game Institute.

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“In such a situation, the trees are stressed, weakened, and there are ideal conditions for the fungus. The mushroom will start spawning and become visible as well. But he lives in the tree for many years before we can see him. It grows through the middle part of the trunk, and when the time is right, it grows up to its edge into the layers of the bark. Inside the bark, the fungus forms a fruiting body – a black mass with a width of several decimeters to meters, called stroma, which is exposed when the outer bark is removed. It is then that we can observe the most typical symptom of the presence of this fungus – a layer of black-brown soot – spores, asexual spores, which, as we found out, thanks to air currents, can move hundreds of kilometers, ”said Dvořák.

Photo: Mendel University archive

Noticeable black stroma develops in the cortex of dying arches (stroma is a macroscopic structure formed by some species of higher fungi).

“It probably won’t hurt a healthy person”

Airborne spores can easily infect other trees. But, as already mentioned, their inhalation can be dangerous for humans.

“It probably won’t harm a healthy person, but it can cause hypersensitivity pneumonitis in sensitive people. If left untreated, it can even lead to death. These cases were recorded as early as the 1940s in North America, where the fungus was first described. Until now, this disease is called maple bark lung, and it is also listed in the International Classification of Diseases,” Dvořák said.

Together with foreign colleagues, the Brno scientists have established cooperation with the state pollen services of the metropolis to find out whether the spread of fungal spores can be monitored by analyzing regularly collected pollen samples.

Photo: Mendel University archive

Tree disease is characterized by prominent black spots on the bark.

“It was possible to obtain samples of daily pollen collections from June to September 2018. We decided not to look for spores under a microscope, as was done before, but to isolate all the DNA. However, it was not easy to isolate enough DNA. Despite this, laboratory diagnostics confirmed the spread of the fungus on the European continent,” added the scientist, who, along with his colleagues from Oregon, USA, is now working on the development of a spore trap.

In addition, it turned out that sooty maple bark disease is not only a European problem. A study trip to the US West Coast confirmed the presence of the fungus, in addition to recently reported cases in the states of Washington and California, as well as in Oregon.

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