Rainstorms Can Lead to Harmful Plant Pathogens?

It has long been suspected, especially among farmers, that rainstorms can lead to harmful pathogens that wreak havoc on plants. And now, research has for the first time caught this phenomenon on camera, and possibly paved the way for disease-resistant crops.

Fungal parasites known as "rust" can grow particularly rampant following rain events, eating away at the leaves of plants like wheat and devastating crop harvests. To better understand the mechanism behind this madness, a team from MIT and University of Liege in Belgium coated a variety of leaves with contaminating fluids and observed what would happen if they were rained on.

High-resolution images of raindrops splashing on these leaves showed that these dewy drops can act as a catapult, scattering contaminated droplets far from their original leaves.

"This could help set separation distances for crops of small plants, such as strawberries, that are usually planted in close proximity," Don Aylor, a scientist of plant pathology and ecology, who was not involved in the study, said in a statement.

"If this were done optimally, ideally you could completely cut the spread to just one neighboring plant, and it would die there," added Lydia Bourouiba, the study's senior author. "One plant could play the role of a shield, and get contaminated, but its mechanical properties would not be sufficient to project the pathogen to the next plant. So you could start reducing the efficacy of spread in one species, while still using agricultural space effectively."

In all, the research team conducted hundreds of experiments on dozens of types of common foliage, including ivy, bamboo, peppermint, and banana leaves. High-speed videography, operating at 1,000 frames per second, captured the sequence of events as raindrops hit each leaf of these plants.

And the more it rains, or the more droplets that are on a plant's surface, the farther its leaves can propel harmful pathogens onto the leaves of unsuspecting neighbors. What's more, researchers found that a plant's mechanical properties - particularly its compliance, or flexibility - also determine how far its pathogens will fly.

By better understanding the mechanics of how rainstorms scatter rust and other pathogens throughout a plant population, farmers may begin to come up with ways of inhibiting the spread of various diseases among their valuable crops.

The results are described in more detail in the Journal of the Royal Society Interface.

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