Finding kinder, gentler microbial friends for
corn plants has led to a strategy for controlling a fungal toxineven
before the crop is planted.
The fungus, Fusarium moniliforme, is especially dangerous if it gets
into corn fed to horses or swine, says ARS microbiologist Charles W. Bacon. While
contamination with the fumonisin toxin produced by F. moniliforme is
rare in the United States, the Food and Drug Administration established
toleranceor maximum allowablelevels as a precaution in early 1999.
Bacon heads the Toxicology and Mycotoxin Research Unit in Athens, Georgia. He
and fellow microbiologist Dorothy M. Hinton found a safe, convenient way to
prevent corn contamination from the moment the seedlings come up. They began
working on the project in 1996.
Now a company is developing a seed treatment with a harmless natural bacterium
that suppresses F. moniliforme. Farmers may have access to the
treatment in a year or two, pending final field tests.
Fusarium thrives inside corn plants, dwelling in spaces between the
cells. And one obstacle to removing it has been that many isolates actually
benefit the plants.
"While the fungus is bad news for mammals, we found that most strains of
it seem to help improve corn root growth," says Bacon. "This better
enables the plant to survive dry conditions and related stress. What we've done
is substitute a bacterium that is harmless to both plants and animals."
Last year, Bacon and Hinton found that a strain of Bacillus subtilis
fills up corn's intercellular spaces before F. moniliforme gets the
opportunity. Scientists call this competitive exclusion.
And the B. subtilis wants the plant all to itself. In petri dishes, it
actually repelled F. moniliforme and may do more for plants' roots
than Fusarium does. The helpful B. subtilis has shown promise
not only in the lab but also in greenhouses and small-scale field plots in
Georgia and Iowa.
Bacon and Hinton filed a patent on the technology, which caught the eye of
Donald S. Kenney, director of technology for Gustafson LLC, a seed treatment
company in Plano, Texas.
"To control fungal toxins in an ear of corn through a seed treatment is
especially interesting to us," says Kenney. "You're protecting the
harvest by doing something far upstream, before the farmer even buys the
Scientists have found other strains of B. subtilis that prevent corn
from being contaminated with Fusarium. But the growing plants would
have to be "vaccinated" with the microorganism through sprays or
other treatments. And that's impractical for farmers.
However, seed treatments are very practical. "We use a fermentation
process to stabilize the bacteria and increase concentrations," says
Gustafson plant pathologist Philip Brannen. "Seed companies would buy the
product from us in a liquid or dried form."
Another benefit is the product's stability. Corn seed sellers get about 10
percent of their product returned from retailers each year, says Kenney.
Pretreated seed may have to be stored a year before it can be resold. The
treatment seems to last at least 2 years, which is plenty of time for
resale.By Jill Lee, formerly with ARS.
This research is part of Food Safety, an ARS National Program (#108)
described on the World Wide Web at