New research reveals how rainfall influences the spread of disease among plants.
High-speed images of raindrops falling on leaves coated with contaminated fluid revealed they can act as dispersing agents, MIT reported. Understanding this relationship could help farmers fight the spread of disease among plants.
"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 Lydia Bourouiba, the Esther and Harold E. Edgerton Career Development Assistant Professor of Civil and Environmental Engineering at MIT. "Polyculture is an old concept if you look at native cultures, 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."
Through rain simulations conducted on dozens of types of foliage, the researchers determined the leaves could not support a thin film of pathogens (as been previously believed), meaning they most likely formed as drops on the surface.
"That can initially seem like a small difference, but when you look at the fluid dynamics of the fragmentation and resulting range of contamination around an infected leaf, it actually changes a lot of the dynamics in terms of the mechanism by which [pathogens] are emitted," Bourouiba said.
The simulations showed when droplets hit a contaminated leaf surface, it launched the pathogens "far and wide." They found a floppier leaf was less effective at creating an arc, or "crescent-moon" of contaminated fluid. On the other hand, at certain rates of flexibility the crescent moon arc changed into one of inertial detachment, causing it to form larger drops that flew farther from the leaf.
The findings allowed the researchers to form a theoretical model to determine the relationship between leaf flexibility and raindrop-induced pathogen dispersal. This suggests the intrinsic mechanical properties of a plant (as opposed to their resistance to pathogens) could be the key to containing these diseases.
"If this were done optimally, ideally you could completely cut the spread to just one neighboring plant, and it would die there," Bourouiba said. "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."
The findings were reported recently in the Journal of the Royal Society Interface.
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