What makes Armillaria ostoyae such a hard to kill fungus


It is called Armillaria ostoyae, and it’s a gnarled parasitic fungus with long black tentacles that spread out and attack vegetation with the ferocity of a movie monster.

His cord-like structures called rhizomorphs seek out and attack trees by sucking up their nutrients. They are known to infect and kill over 600 types of woody plants, posing a significant threat to forests and the agricultural industry. From 2000 to 2002, the fungus alone caused $ 1.5 million in damage to Georgia peach trees.

We didn’t know much about what makes Armillaria ostoyae so hard to kill, until now. A team of researchers led by Steven Naleway, an assistant professor of mechanical engineering at the University of Utah (U of U), studied the tree’s fungus defense mechanism to better understand what makes it so hearty. Their discoveries were published in the latest edition of the Journal of the Mechanical Behavior of Biomedical Materials.

The fungus, which sprouts golden “honey mushrooms” above the surface in the fall, is known to grow just about anywhere. But researchers at the U of U have sampled it from what may be the largest known specimen, a huge growth in the Malheur National Forest in eastern Oregon, which has an area of ​​3. , 5 square miles and weighing 35,000 tons. The specimen, known as the “humongous fungus,” is possibly the largest living organism on Earth, scientists say.

Black rhizomorphs use enzymes and pressure to penetrate the surface of roots and under the bark of trees, said Debora Lyn Porter, a doctoral student in mechanical engineering at the U of U, who is the lead author of the article. . Once inside the tree, it leaves a mycelial fan, white branched filaments that coat the inside of the bark like paint, depriving the tree of water and nutrients.

“Once it starts, it’s very difficult to uproot it,” Porter explains. Farmers, she adds, may continue to prune the growing tentacles, but they keep growing back.

Much of the past and current research on the species has focused on its biology and ecology, life cycle, interactions with the environment, and methods of control, which have not worked well in the past. But Naleway’s team wanted to focus on the biomechanical structure of tendrils, or rhizomorphs.

Rhizomorphs have a melanized outer layer that protects the tendrils from chemicals and mechanical forces. “This outer layer is pretty tough,” says Naleway. “It’s a bit like tough plastic. For the natural world, this is strong enough.

They learned that the outer layer of rhizomorphs is less porous near the surface but more porous in the inner layer, so they can still soak up water and nutrients. Researchers have also learned that they contain calcium, which can protect against acid attacks from insects and chemical compounds.

Naleway hopes that farmers, forestry officials and pest control developers armed with this new knowledge can find a more effective method of containing this resilient fungus.

“If you want to have some kind of human biocontrol, you have to fight that calcium and get into that outer surface better,” he says.

– This press release originally appeared on the University of Utah website

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