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GM crops and mycotoxins



Given the recent debate on this server about GM crops in developing
countries, I thought the following was especially interesting, particularly
the points about GM crops diminishing mycotoxin food contamination and the
links of  mycotoxin to esophageal cancer in many parts of South Africa,
followed by a report on the reduction of mycotoxins in Bt corn.

Rick


from
       INFORMATION SYSTEMS FOR BIOTECHNOLOGY

                  ISB News Report
                   December 1999


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FOOD FOR THOUGHT

`Gene Technology -- Food for Thought' was the title of a
conference hosted by the Consumer Institute of South Africa in
October 1999. Although initially dominated by speakers who
cautioned against use of genetically modified (GM) crops, the
conference ended with organizers calling for more public education
on GM food issues.

The keynote speakers were Dr. Michael Hansen, from the US
Consumers' Union, and Dr. John Fagan, of the Maharishi University
of Management in Fairfield, Iowa and founder of Genetic ID, a
company that tests foods for the presence of foreign DNA and
protein. The two speakers voiced many concerns relative to GM
crops, such as instances of lower than expected yields from
herbicide resistant cultivars; the damaging effects of agricultural
monocultures on biodiversity; the influence of multinational seed
companies on countries' economies; and the demise of the
small-scale farmer.

Dr. Fagan argued that the introduction of even a single foreign
gene into a plant could alter that crop's entire metabolic pathways
in totally unforeseen ways. Dr. Hansen stated it was na´ve to think
that the world could not produce enough food without GM
technology, asserting instead that shortages result from poor food
distribution. In addition, he commented that the segments
benefiting from GM foods were the seed companies and the
farmers.

Other speakers, however, espoused different perspectives,
indicating that food distribution in Africa is also hampered by lack of
physical infrastructure, as well as political turmoil and corruption in
many countries. Some participants felt that purported yield
increases and the ability to grow crops in marginal areas, both
potential benefits of GM technology, were essential requirements
for feeding Africa's population. However, it was likewise noted that
GM foods are not a "quick fix" and only part of the long-term
solution.

Participants acknowledged that though the first generation of GM
foods do not benefit the consumer directly, second generation
crops currently under investigation should. Rice with higher vitamin
A content, maize with enhanced essential amino acid levels, and
plants with improved oils were some of the examples cited of the
next wave of GM crop attributes.

One speaker, Muffy Koch, Director of Innovation Biotechnology,
spoke of the benefits of planting insect tolerant GM crops. She
emphasized reports of decreased pesticide use, which can result in
increased biodiversity, and noted that a decrease in insect damage
to GM crops may also reduce post-harvest fungal infection, thus
diminishing mycotoxin food contamination, which has been linked to
esophageal cancer in many parts of South Africa. She pointed out
that use of GM crop technology was appropriate for both
commercial and small-scale, resource-poor farmers.

Considerable concern was expressed that multinational
corporations could control agricultural output worldwide through
ownership of plant genome patents, and it was suggested that
developing countries be exempt from patent restrictions. Another
concern mentioned was the exploitation of indigenous plant
genomic resources with no recompense to Africa.

Participants largely agreed that labeling of GM foods was
necessary to allow consumer choice, and acknowledged that the
agreement to label GM food in New Zealand and Australia was not
made on the basis of any recorded public health or safety
concerns, but on consumer information grounds. An allergist, Dr.
Harris Steinman, talked of the fear of unintentionally introducing or
creating allergens in GM foods, pointing out that some allergens
are very stable and might not be destroyed by the cooking
process.

Many participants expressed dismay that the GMO Act, passed in
South Africa in 1997, had not yet been implemented. SAGENE
(South African Genetic Experimentation Committee), the former
regulatory body, has been trying to "hold the fort" in the interim.
The Department of Agriculture has indicated that the act will be
implemented before the end of 1999. Until then, all applications for
new GM trials and commercial releases are currently "on hold."

An environmental lawyer, Mariam Mayet, representing Biowatch, a
South African organization opposed to the use of GM food,
stressed the importance of using the precautionary principle, which
states that if there is any scientific uncertainty regarding the
possible harm to human health or the environment, caution must
be exercised.

Throughout the course of the meeting, the need for public
education became increasingly clear. However, in a country such
as South Africa in which consumers range from the illiterate to
savvy internet users, education challenges are extensive. In her
summation, Diane Terblanche, the Chief Executive Officer of the
South African Consumer Institute, pledged her organization's help
in the education process, thus ending the conference with a
renewed commitment from most participants to continue to
investigate the advantages and disadvantages of GM foods.

Jennifer A. Thomson
Department of Microbiology
University of Cape Town
jat@molbiol.uct.ac.za

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THE GOOD NEWS ABOUT Bt CORN

Recently, non-target effects of Bt corn have become the subject of
a great deal of debate and this debate has fueled opposition to Bt
corn and genetically modified crops in general. Non-target effects,
however, are not all bad. In fact, we have found that Bt
transformation of corn hybrids can actually enhance their safety as
food products because Bt corn hybrids are significantly less likely
to contain harmful mycotoxins than their non-Bt counterparts.

When insects attack corn plants, one result is an increase in
diseases. This occurs because insect pests carry pathogenic fungi
and predispose plants to disease development. These diseases
include ear rots and stalk rots that can reduce corn yield and
quality. Some of the diseases are caused by fungi that produce
mycotoxins in the corn crop. Mycotoxins, which are toxic
compounds produced by fungi, pose a significant problem
worldwide, affecting an estimated 25% of grain crops.

The major mycotoxins in corn include aflatoxins, produced by fungi
in the genus Aspergillus, and fumonisins, produced by several
species of Fusarium fungi. Both aflatoxins and fumonisins can be
fatal to livestock and are probable human carcinogens. The
importance of fumonisins in human health is still a subject of
debate, but they are carcinogenic to laboratory animals and there
is evidence that they contribute to human cancer in some parts of
the world. Fumonisin concentrations in corn are or will be under
regulatory scrutiny in several nations. The economic impact of
aflatoxins has been greater than that of fumonisins because many
nations already have regulations on allowable aflatoxin
concentrations in crops. Symptoms of Fusarium and Aspergillus
ear rots are often highly correlated with insect damage.

Since 1994, we have been studying the influence of Bt expression
on Fusarium ear rot and fumonisins in corn. In these studies,
differences among types of Bt genes (or Bt events) have become
evident. All Bt events are not alike. They differ in the specific Bt
protein they express and in the tissue-specific expression of the
proteins. Kernel expression of Bt proteins appears to be an
important factor determining the amount of kernel feeding by
European corn borer larvae and subsequently the intensity of
Fusarium infection.

Results of our studies have consistently demonstrated that hybrids
containing two of the Bt events (MON810 and BT11) experience
significantly less Fusarium ear rot and yield corn with lower
fumonisin concentrations than their non-Bt counterparts. Similar
results have been obtained in studies conducted in Illinois and
North Carolina (1, 2, 3). When conventional hybrids were subjected
to high populations of European corn borers, Fusarium ear rot
severity and fumonisin concentrations became elevated, often to
levels considered unsafe for swine and horses. Levels considered
safe for horses and swine are <5 ppm and <10 ppm, respectively.
Safe fumonisin levels for humans are unknown (4). Fusarium ear
rot and fumonisin levels in MON810, CBH351, and BT11 hybrids
were uniformly low (usually less than 10% of the concentrations in
the non-Bt hybrids) and were unaffected by European corn borer
populations.

Other studies also have shown reduced kernel infection by A.
flavus and lower aflatoxin concentrations in BT11 and MON810
hybrids compared with their non-Bt counterparts. However, these
reductions have been less dramatic than those seen for fumonisins
(5).

Although the results described here support the utility of Bt hybrids
for management of Fusarium and Aspergillus ear rots and stalk
rots of corn, it should be emphasized that these diseases all
require an integrated management approach involving other
tactics. When conditions are very favorable for disease, protection
from insect damage may not be enough. Another limitation of Bt
corn hybrids is their spectrum of activity. Currently available events
are not effective against the full spectrum of insects that can
contribute to kernel damage and subsequent mycotoxin
contamination.

Future Directions

Bt hybrids can be an important tool in the integrated management
of Fusarium and Aspergillus ear rots. New Bt hybrids now under
development promise to exhibit more complete control of other
kernel-feeding insects, so they should provide even better
protection from insect-associated fungi, and there could be further
contributions toward mycotoxin management. Transgenic control of
insects and diseases offers an alternative that is much more
effective, consistent, economical, and environmentally sound than
foliar insecticides.

Debate surrounding the use of genetically modified crops should
be based on an assessment of all risks and benefits that can be
measured, including environmental impacts, livestock impacts, and
potential human health threats. Available data show that Bt
transformation of corn hybrids enhances the food and feed safety
of the grain by reducing its vulnerability to mycotoxin-producing
fungi. A common criticism of currently available genetically modified
crops is a lack of apparent benefits to consumers. But lower
mycotoxin concentrations represent a clear benefit to consumers of
Bt grain, whether the intended use is for livestock or human food
products. Consumers and regulatory agencies should consider
these factors in decisions regarding Bt corn use.

Sources

1. Dowd PF and Munkvold GP. 1999. Associations between insect
damage and fumonisin derived from field-based insect control
strategies. Proceedings of the. 40th Annual Corn Dry Milling
Conference, June 3-4, 1999. Peoria, IL.

2. LSI Health and Environmental Sciences Institute. 1999. An
evaluation of insect resistance management in Bt field corn: A
science-based framework for risk assessment and risk
management. Washington, DC: ILSI Press.

3. Munkvold GP, Hellmich RL, and Rice LG 1999. Comparison of
fumonisin concentrations in kernels of transgenic Bt maize hybrids
and non-transgenic hybrids. Plant Diseases 83:130-138.

4. Munkvold GP, and Desjardins AE. 1997. Fumonisins in maize:
Can we reduce their occurrence? Plant Diseases 81:556-565.

5. Windham GL, Williams WP, and Davis FM. 1999. Effects of the
southwestern corn borer on Aspergillus flavus kernel infection and
aflatoxin accumulation in maize hybrids. Plant Diseases
83:535-540.

Gary P. Munkvold
Department of Plant Pathology
Iowa State University
munkvold@iastate.edu

Richard L. Hellmich
USDA-ARS Corn Insects and Crop Genetics
Research Laboratory & Iowa State University
rlhellmi@iastate.edu



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