Secret behind fungal spore cannons revealed

Merging water droplets leap off the ground.
Spores use the physics of merging droplets to launch themselves out into the world.
Credit: Chuan-Hua Chen, Duke University

Researchers at Duke University in the United States have used an inkjet printer and high-speed cameras to solve the century-old mystery of how fungal spores can launch themselves clear of their parents.

In a process first observed by British-Canadian mycologist Reginald Buller more than 100 years ago, fungal spores can hurl themselves a few crucial millimetres directly away from their parents using nearby water droplets.

Exactly how this occurred has remained unclear, partly because the spores and water droplets are so small, but also because the event happens in a microsecond, too fast even for most high-speed cameras.

To overcome this, a team lead by Chuan-Hua Chen at Duke University constructed a custom polystyrene ‘spore’ larger than the naturally occurring type. A small droplet of water was then added.

An inkjet printer was used to gradually build a Buller drop, named for the mycologist that discovered it, next to the ‘spore’. Controlling the droplet size allowed the researchers to regulate the speed and timing of the launch so it could be recorded.

At just the right moment, the spore’s water droplet and Buller drop merged, causing a release of surface tension energy that then propelled the spore in a direction aligned with its flat face. This was the secret behind the explosive speed.

“The release of energy is so rapid that it accelerates the entire system with a million gs, but there’s so much air drag that the spore still only travels a few millimeters at most. That’s why it’s so important for the spores to shoot directly away from the fungus,” said Chen.

The research is published in the Journal of the Royal Society Interface.

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