Watch ‘tiny tornadoes’ spread plant pathogens

Pathogens and germs don’t just make humans and animals sick. Diseases from bacteria and fungi can wreak havoc on all kinds of plants. One particularly bad pathogenic fungus for plants is called rust. This is not the same rust you can find on metals, but it has a similar bright red, orange, yellow, and brown color that can take away from a more decorative plant’s appearance. Importantly, it can also wipe out important crops including wheat and barley.

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Rust is airborne–just like COVID-19–and it spreads to healthy plants by way of cells called spores. Understanding how these spores move around is key to designing better ways to protect plants. Using high-speed cameras, a study published January 31 in the journal Science Advances analyzed how plant spores are dispersed. It revealed how tiny ‘tornadoes’ spread pathogens from infected plants to healthy ones.

Small, tornado-like swirls scatter spores and pollen around a wheat plant leaf. CREDIT: Bio-inspired Fluid Lab/Cornell University

When a raindrop hits a leaf of a wheat plant that is infected with rust, the leaf will flutter and create these tiny swirling vortices of air that spreads the spores around. Like virus particles in a sneeze of cough, they can then infect healthy plants.

In the study, a team from Cornell University used a high-speed camera to analyze this process. It could be a step towards designing a strategy to help reduce pathogens from viruses, bacteria, and oomycete fungi from spreading from a plant’s leaves.

The footage enabled the team to predict the trajectory of the spores and how they are carried by the swirling cyclone-like vortex created by the leaves. The team used techniques that are usually used to study geophysical flows–large-scale oceanic and atmospheric air currents like the jet stream. They downsized these airflows by a few orders of magnitude to both understand and predict the swirls in the air around a bouncing wheat leaf.

“It’s kind of a tiny tornado in the air,” study co-author and Cornell University biophysicist Sunghwan Jung, said in a statement. “We describe the magnitudes of these kinds of swirling motion, and then when they will form and how spores move around, so everything is predictable.”

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The team used miniature hollow glass particles to mimic actual spores due to restrictions to working with live spores. This method helped them gauge how many spores might come off a leaf, what direction they may fly in, and how they travel away from an infected plant.

The team hopes that the data from this study could help develop new methods for keeping spores from infecting healthy plants that go right to the source of the spore dispersal.

“We couldn’t figure out the solution yet,” said Jung. “But if we can control these kinds of vortex structures around the leaf somehow, then we can reduce the spread of spores to new plants.”