New Orleans, Louisiana
April 16, 2008
The spiraling use of corn for food
and fuel is creating heightened concerns about contamination of
this staple crop with deadly aflatoxin. Produced by certain
fungi that grow on corn, this contaminant is a known human
carcinogen that especially threatens food safety in the
developing world and can potentially cause the loss of hundreds
of millions of dollars in the United States each year.
Bruce Hammond, Ph.D., a lead researcher at
Monsanto’s Product Safety
Center, says that aflatoxin is a potent liver carcinogen and
source of other health concerns in humans and animals. Tightly
regulated by the FDA, Hammond said threatening levels of the
contaminant are kept out of the food supply in the United
States. But in Africa and the developing world, poor regulation
has made aflatoxin a significant food safety issue.
At the 235th national meeting of the
American Chemical Society in
New Orleans, Hammond and others presented advances towards the
production of corn less susceptible to aflatoxin contamination.
The new varieties could contribute to the reduction of the
worldwide threat of the deadly toxin, improve food quality in
developing countries and increase corn yield for food and in the
United States.
Growing conditions in Africa are well-suited for Aspergillus
flavus, the fungus that produces aflatoxin. Environmental
factors like drought, high temperatures, nitrogen availability
and insect damage in plants allow the fungus to thrive. Fungal
spores can enter the corn via cavities created by insects, and
later germinate and produce mycotoxins, the problematic family
of contaminants that includes aflatoxin.
In Africa, where both animals and man eat feed corn, people die
as a result of acute aflatoxin exposure. In 2007, there were
over a hundred deaths in Kenya alone. Levels of the liver toxin
rise to especially dangerous levels in those with hepatitis.
However, the contaminant poses the biggest threat to children.
“There are studies documenting the correlation between growth
issues in West African children and ingestion of aflatoxins,”
said Robert L. Brown, a plant pathologist at the United States
Department of Agriculture who studies genes that might confer
aflatoxin resistance in corn. He also said the toxin has an
effect on immune function in children. Brown is in the process
of releasing six new corn inbred lines that are the result of
crosses between U.S. aflatoxin-resistant lines and African
resistant lines. These new inbreds have been selected for valued
crop characteristics as well as for resistance.
Estimates suggest that 4.5 billion people in developing
countries are chronically exposed to aflatoxin. While the health
threat looms in developing nations, it is also a significant
economic threat to agriculture in the United States.
“Because of climate, you can find an aflatoxin breakout
somewhere in the southern U.S. pretty much every year,” said
Brown. These outbreaks can drive up prices for ethanol if it’s
feed corn byproducts become contaminated.
In the quest to engineer better corn crops, scientists at
Monsanto are targeting insect pests that can rob corn yield and
decrease grain quality. The first generation of their so-called
“Bt corn” incorporated a gene into the corn genome from Bacillus
thuringiensis (Bt), a soil microbe that produces a protein that
kills harmful corn pests like the European and southwestern corn
borer. Bt is the active ingredient in microbial pesticides
widely used in organic and conventional agricultural systems for
close to 50 years.
“Bt is found commonly in the environment already. After
inserting the gene into the corn plant, the crop makes an insect
control protein within the plant that helps protect it from
target species like European corn borer, but doesn’t harm other
non-target insects or species. The use of this technology has
also allowed farmers to decrease other forms of pesticide
protection, helping the environment in the process,” said
Hammond.
The Bt corn successfully resisted insect damage by the European
corn borer, rootworm and other insects that allow
mycotoxin-producing fungi to infect corn plants. Now, varieties
of Bt corn make up 55 to 60 percent of all corn grown in the
United States each year, according to Hammond.
Subsequent studies confirmed a secondary benefit — with less
insect damage on corn ears, the Bt corn suffered less fungal
infection and had lower levels of certain mycotoxins, but not
aflatoxin. Hammond’s team followed up on these observations with
the aim to reduce aflatoxin levels.
Today, Monsanto researchers aim to confer even more insect
protection to the second generation of Bt corn. Pending
regulatory approval, the new varieties could include additional
genes that guard against a broader variety of pests like the
fall armyworm, a particular threat to the southern United States
associated with aflatoxin contamination.
Preliminary trials found that the new Bt corn variety had
reduced levels of aflatoxin, said Hammond. Other sites in the US
and in Argentina also showed lower insect damage to the corn
from other pests.
“These preliminary results are encouraging, and we look forward
to more trials performed under a variety of environmental
conditions to show that these reductions are reproducible,” said
Hammond.
The researcher’s future efforts aim to lessen the effect of
other environmental stressors that can trigger fungal growth in
plants.
“If we take insect protection, combine it with drought
tolerance, protect the roots against root damage, have herbicide
resistance and improved nitrogen utilization all in the same
plant, maybe we will have plants that are much less susceptible
to these stress factors and, as a secondary effect, reduced
mycotoxin contamination,” said Hammond.
The American Chemical Society — the world’s largest
scientific society — is a nonprofit organization chartered by
the U.S. Congress and a global leader in providing access to
chemistry-related research through its multiple databases,
peer-reviewed journals and scientific conferences. Its main
offices are in Washington, D.C., and Columbus, Ohio. |
|