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Instead of Coughing on Each Other, Plants Spread Disease Through Raindrops

Watch how raindrops catapult off leaves in slow motion.

​Rainfall is an essential ingredient of a healthy farm, but it has a dark side too. When water droplets hit the leaves and petals of diseased or infected plants, they become a powerful vessel of disease transmission. Apparently, this connection between rain and parasitic outbreaks has been anecdotally acknowledged b​y farmers for decades, but the mechanics behind the process weren't mapped out in any detail until this week.

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On Wednesday, the Massachusetts Institute of Technology released a video overview of an experim​ent conducted by mathematicians Lydia Bourouiba and Tristan Gilet (the pair's results were publish​ed in The Journal of The Royal Society Interface on February 4).

The upshot is that Bourouiba and Gilet imaged simulated raindrops impacting with a wide range of different plant surfaces in high resolution, capturing the splash dynamics with 1,000 frames per second.​

Slow motion raindrop projectiles

Of the species they tested, which included ivy, banana leaves, ba​mboo, and peppermint, the mathematicians discovered that there was a big difference in disease-spreading potential depending on the size and flexibility of the leaf—that is, its capacity to catapult pathogens to neighboring plants.

This, in turn, suggests that there is an optimal way to arrange crops in order to minimize the risk of rain-enabled epidemics. "We can start thinking of how to smartly reinvent polyculture, where you have alternating species of plants with complimentary mechanical properties at various stages of their growth," said Bourouiba in an M​IT statement.

"Polyculture is an old concept if you look at native cultures," she continued, "but this is one way to scientifically show that by alternating plants in one field, you can mechanically and naturally reduce the range of transmission of a pathogen during rainfall."

The research's application to curbing agricultural outbreak is great and all, but the video is worth a watch as much for the slow motion raindrop projectiles. Much like the recent study into the aerosol-r​eleasing magic of rainfall, which was also produced by MIT, Bourouiba and Gilet have revealed what a complex, influential impact raindrops have on the microscale.