BERKELEY — Long before geese started flying in chevron formation or cyclists learned the value of drafting, fungi discovered an aerodynamic way to reduce drag on their spores so as to spread them as high and as far as possible.
In a few tenths of a second, Sclerotinia expels hundreds of thousands of spores in a plume that can rise 10 cm, much higher than any single spore by itself. At right, the spores ejected first (blue) do not travel far, but they create a wind that carries spores released milliseconds later (yellow) much higher, and the final spores (red) even higher. Filmed at 3,000 frames per second. (Mahesh Bandi, Agnese Seminara/Harvard University and Marcus Roper/UC Berkeley)
One fungus, the destructive Sclerotinia sclerotiorum, spews thousands of spores nearly simultaneously to form a plume that reduces drag to nearly zero and even creates a wind that carries many of the spores 20 times farther than a single spore could travel alone, according to a new study by mathematicians and biologists from the University of California, Berkeley, Harvard University and Cornell University.
"In the Tour de France, riders form a peloton that can reduce air drag by 40 percent," said co-lead author Marcus Roper, a postdoctoral researcher in the Department of Mathematics at UC Berkeley and at Lawrence Berkeley National Laboratory. "The ascospores of Sclerotinia do the peloton perfectly, reducing air drag to zero and sculpting a flow of air that carries them even farther."
Presumably, this strategy helps the fungi get their spores off the ground into the foliage of their host plants, or into airstreams that can carry them to host plants, the scientists say.
Co-lead author Agnese Seminara, a postdoctoral researcher and theoretical physicist in Harvard’s School of Engineering and Applied Sciences, added: "I realized that the spores behaved much like cloud droplets. To follow their paths, I adapted algorithms I had developed to describe cloud formation."
Roper, Seminara, and colleagues report the findings this week in the early online edition of the journal Proceedings of the National Academy of Sciences (PNAS).
"These findings could have implications for methods of controlling the spread of fungal pathogens," said senior author Anne Pringle, associate professor of organismic and evolutionary biology at Harvard. "Sclerotinia alone costs U.S. farmers on the order of $1 billion annually, including costs of controlling the fungus and crop losses. Research directed at understanding how to disrupt the cooperative ejection of spores may provide novel tools for the control of these fungal pathogens."
Researchers in the field of bioballistics how plants, fungi and animals accelerate seeds, spores or even parts of their body to high speed have found an amazing variety of techniques to overcome friction with the air, the main limitation for small spores and seeds.
"Understanding how Sclerotinia is discharging its spores and getting them onto the plants will eventually lead us to new ways of looking at plant architecture," said co-author Helene Dillard, a plant pathologist who heads Cornell University’s Cooperative Extension and is associate dean of the College of Agriculture and Life Sciences. "When plant breeders are developing new varieties of crops such as beans, cabbage or sunflowers they can keep in mind how Sclerotinia gets the spores to reach their targets, which is usually the flowers."
Scientists have recognized for more than 100 years that many spore-producing fungi the ascomycetes release their spores in plumes that carry them long distances. More than 50 years ago, scientists noted that these spore plumes create a wind of their own, but the physics of the plumes was not understood, Roper said. In addition, little work has been done on how seeds or spores cooperate to improve dispersal to new environments.