These high-speed video images enabled Roper and Seminara to model spore plume movement precisely with standard equations of hydrodynamics. They showed that the thousands of spores ejected at the same time quickly eliminate all drag and allow the spores to travel about a centimeter, by which time the wind generated by the spores captures and whisks them to a speed of 60 centimeters per second. Their upward motion is stopped only by gravity, Roper said.
The added range from "hydrodynamic cooperation" allows fungi on the ground to shoot their spores into flowers or plant wounds, whence they can quickly spread throughout the plant and kill it.
Often called white mold, Sclerotinia rot, or wilt, the fungus attacks more than 400 species of plants, Dillard said, including beans, sunflowers, soybeans, canola and peanuts, and can wipe out entire fields. In spring and summer, the fungus produces cups (apothecia) about one-half centimeter across that spew spores into the air to infect plants. The fungus produces overwintering seed-like bodies called sclerotia on the infected plant tissues.
"It grows across a cabbage head and produces these small sclerotia that look like mouse droppings," Dillard says. "The sclerotia fall on the ground, and are then in position to initiate the infection process the following year."
The researchers were also curious how fungi manage to eject their spores simultaneously. To investigate this, they grew another mold, a coprophilic fungus from the genus Ascobolus, on horse dung and focused their high-speed video camera on the two-millimeter, cup-shaped fruiting body containing tens of thousands of spore sacs (asci), each containing eight spores. They found that, while the spore sac that ejects first seems to be random, after the first one or two go off, a wave of ejectio
|Contact: Robert Sanders|
University of California -- Berkeley