Genetically modified maize
Genetically modified maize (corn) is a genetically modified crop - in other words, specific maize strains have been genetically engineered with agronomically desirable traits. Corn that is resistant to herbicides has been developed, as has corn that expresses insecticidal proteins from Bacillus thuringiensis bacteria. While GM maize has been widely adopted by farmers in countries where it has been approved, it has also caused controversy with respect to possible effects on health, nontarget insects, and other plants via gene flow. One strain, called Starlink, was approved only for animal feed in the US, but was found in food, leading to a series of recalls starting in 2000.
- 1 Marketed Products
- 2 Products in development
- 3 Development of resistance
- 4 Regulation
- 5 Controversy
- 6 See also
- 7 References
- 8 Further reading
- 9 External links
Herbicide resistant corn
Corn varieties resistant to glyphosate herbicides (the original of which are Roundup) were first commercialized in 1996 by Monsanto, and are known as "Roundup Ready Corn". Bayer CropScience developed "Liberty Link Corn" that is resistant to glufosinate. Pioneer Hi-Bred has developed and markets corn hybrids with tolerance to imidazoline herbicides under the trademark "Clearfield" - though in these hybrids, the herbicide-tolerance trait was bred using tissue culture selection and the chemical mutagen ethyl methanesulfonate not genetic engineering. Consequently, the regulatory framework governing the approval of transgenic crops does not apply for Clearfield.
As of 2011, herbicide-resistant GM corn was grown in 14 countries. By 2012, 26 varieties herbicide-resistant GM maize were authorised for import into the European Union. but such imports remain controversial even though in 2012 the EU was reported to import 30 million tons a year of GM crops and cultivation of herbicide-resistant corn in the EU provides substantial farm-level benefits.
Bt corn is a variant of maize that has been genetically altered to express one or more proteins from the bacteria, Bt. The protein is poisonous to certain insect pests and is widely used in organic gardening. In the case of corn, the pest is the European corn borer, which causes about a billion dollars in damage each year. In recent years, traits have also been added to ward off Corn ear worms and root worms, the latter of which also causes about a billion dollars in damages in each year.
The Bt protein is expressed all through the plant. When a target insect eats the Bt-containing plant, the protein is activated in the gut of the insect, which is alkaline (human guts are acidic), and in the alkaline environment the protein partially unfolds and is cut by other proteins, forming a toxin that paralyzes the insect's digestive system and forms holes in the gut wall. The insect stops eating within a few hours and eventually starves to death.
In 1996, the first GM maize producing a Bt cry protein was approved, which killed the European corn borer and related species; subsequent Bt genes were introduced that killed corn rootworm larvae.
The Bt genes that have been engineered into crops and approved for release include the following, singly and stacked (event name between brackets): Cry1A.105 (MON89034), CryIAb (MON810), CryIF (1507), Cry2Ab (MON89034), Cry3Bb1 (MON863 and MON88017), Cry34Ab1 (59122), Cry35Ab1 (59122), mCry3A (MIR604), and Vip3A (MIR162), and the engineered crops include corn and cotton.:285ff Corn genetically modified to produce VIP was first approved in the US in 2010. Monsanto developed a soybean expressing Cry1Ac and the glyphosate-resistance gene for the Brazilian market, which completed the Brazilian regulatory process in 2010.
Products in development
Development of resistance
By US EPA regulation, farmers who plant Bt corn must plant non-Bt corn nearby (called a "refuge") to provide a location to harbor pests The theory behind these refuges is to slow the evolution of the pests' resistance to the Bt pesticide. EPA regulations also require seed companies to train farmers how to maintain refuges, to collect data on the refuges, and to report that data to the EPA. A study of these reports found that from 2003 to 2005 farmer compliance with keeping refuges was above 90%, but that by 2008 approximately 25% of Bt corn farmers did not keep refuges properly, raising concerns that resistance would develop.
In November 2009, Monsanto scientists found the pink bollworm had become resistant to the first generation Bt cotton in parts of Gujarat, India - that generation expresses one Bt gene, Cry1Ac. This was the first instance of Bt resistance confirmed by Monsanto anywhere in the world. Bollworm resistance to first generation Bt cotton has also been identified in the Australia, China, Spain and the United States. In 2012, a Florida field trial demonstrated that army worms were able to eat pesticide-containing GM corn produced by Dupont-Dow without any ill effects, meaning they had become resistant to it; armyworm resistance was first discovered in Puerto Rico in 2006, prompting Dow and DuPont to voluntarily stop selling the product on the island,
The regulation of genetic engineering concerns the approaches taken by governments to assess and manage the risks associated with the development and release of genetically modified crops. There are differences in the regulation of GM crops between countries, with some of the most marked differences occurring between the USA and Europe. Regulation varies in a given country depending on the intended use of the products of the genetic engineering. For example, a crop not intended for food use is generally not reviewed by authorities responsible for food safety.
There is broad scientific consensus that food on the market derived from GM crops poses no greater risk to human health than conventional food. GM crops also provide a number of ecological benefits.
Critics have objected to GM crops per se on several grounds, including ecological concerns, and economic concerns raised by the fact these organisms are subject to intellectual property law (although this latter issue applies equally to any plant variety). GM crops also are involved in controversies over GM food with respect to whether food produced from GM crops is safe and whether GM crops are needed to address the world's food needs. See the genetically modified food controversies article for discussion of issues about GM crops and GM food. These controversies have led to litigation, international trade disputes, and protests, and to restrictive legislation in most countries.
Debate over the effects of Bt corn on nontarget insects
One of the major uses of GM crops is in insect pest control though the expression of the cry (crystal delta-endotoxins) and cyt (cytolysins) genes from Bacillus thuringiensis (Bt). There are concerns that these toxins could target predatory and other beneficial or harmless insects as well as the targeted pest insect. The proteins produced by Bt have been used as organic sprays for insect control in France since 1938 and the USA since 1958 with no ill effects on the environment reported. While cyt proteins are toxic towards the insect orders Coleoptera (beetles) and Diptera (flies), cry proteins selectively target Lepidopterans (moths and butterflies). As a toxic mechanism, cry proteins bind to specific receptors on the membranes of mid-gut (epithelial) cells resulting in rupture of those cells. Any organism that lacks the appropriate receptors in its gut cannot be affected by the cry protein, and therefore Bt. Regulatory agencies assess the potential for the transgenic plant to impact non target organisms before approving their commercial release.
In 1999 a paper was published in Nature showing that in a lab environment pollen from Bt maize dusted onto milkweed could harm the monarch butterfly. A collaborative research exercise was carried out over the next two years by several groups of scientists in the US and Canada, looking at the effects of Bt pollen in both the field and the laboratory. This resulted in a risk assessment that concluded that any risk posed by the corn to butterfly populations under real-world conditions was negligible. A 2002 review of the scientific literature concluded that "the commercial large-scale cultivation of current Bt–maize hybrids did not pose a significant risk to the monarch population" and noted that despite large-scale planting of GM crops, the butterfly's population is increasing.
Issues of gene flow have arisen in two contexts with respect to GM maize: the interaction between GM maize and varieties in Mexico, and the question of gene flow into refuges.
In 2009 the government of Mexico created a regulatory pathway for approval of genetically modified maize, but because Mexico is the center of diversity for maize, concerns have been raised about the effect that genetically modified maize could have on local strains. A 2001 report in Nature presented evidence that Bt maize was cross-breeding with unmodified maize in Mexico, although the data in this paper was later described as originating from an artifact and Nature stated that "the evidence available is not sufficient to justify the publication of the original paper". A subsequent large-scale study, in 2005, failed to find any evidence of contamination in Oaxaca. However, other authors have stated that they also found evidence of cross-breeding between natural maize and transgenic maize.
In 2004, Charles Chilcutt and Bruce Tabashnik published a communicated paper in Proceedings of the National Academy of Sciences of the United States of America describing findings of Bt protein in kernels of refuge corn (a stand of non-genetically modified corn planted alongside a genetically modified field to prevent or slow the development of predators resistant to its modified properties by purposely encouraging the mating of species across said crops), and raised concerns about gene flow from Bt to unmodified corn varieties.
Concerns about safety of eating GM corn
The French High Council of Biotechnologies Scientific Committee reviewed the 2009 Vendômois et al. study and concluded that it "..presents no admissible scientific element likely to ascribe any haematological, hepatic or renal toxicity to the three re-analysed GMOs." However, French government applies a principle of precaution against GMOs. A review by Food Standards Australia New Zealand and others of the 2009 Vendômois et al. study concluded that the results were due to chance alone.
A 2011 Canadian study looked at the presence of CryAb1 protein (BT toxin) in non-pregnant women, pregnant women and fetal blood. All groups had detectable levels of the protein in blood, including 93% of pregnant women and 80% of fetuses at concentrations of 0.19 ± 0.30 and 0.04 ± 0.04 mean ± SD ng/ml, respectively. The paper did not discuss safety implications or find any health problems. The paper has been found to be unconvincing by several authors and organizations. In a swine model, Cry1Ab-specific antibodies were not detected in pregnant sows or their offspring and no negative effects from feeding Bt maize to pregnant sows were observed.
StarLink is a genetically modified maize, containing a variant of the Bacillus thuringiensis (Bt) protein called Cry9C that had not been used in a GM crop before. Starlink's creator, Plant Genetic Systems (bought by AgrEvo which then became Aventis CropScience during the time of the incident,:15–16 which was eventually bought by Bayer), had applied to the US Environmental Protection Agency (EPA) to market Starlink for use in animal feed and in the human food supply.:14 However, because the Cry9C protein lasts longer in the digestive system before breaking down than other Bt proteins, the EPA had concerns about its allergenicity, and PGS did not provide sufficient data to prove that Cry9C was not allergenic.:3 As a result PGS split its application into separate permits for use in food and use in animal feed only. Starlink was approved by the EPA for use in animal feed only in May 1998.:15
StarLink corn was subsequently found in food destined for consumption by humans in the US, Japan, and South Korea.:20–21 This corn became the subject of the widely publicized Starlink corn recall, which started when Taco Bell-branded taco shells sold in supermarkets were found to contain the corn, resulting in sales of StarLink seed being discontinued. The registration for the Starlink varieties was voluntarily withdrawn by Aventis in October 2000.
51 people reported adverse effects to the FDA; these reports were reviewed by the US Centers for Disease Control (CDC), which determined that 28 of them were possibly related to Starlink. However, the CDC studied the blood of these 28 individuals and concluded there was no evidence the reactions these people experienced were associated with hypersensitivity to the Starlink Bt protein.
A subsequent review of these tests by the Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel points out that while "the negative results decrease the probability that the Cry9C protein is the cause of allergic symptoms in the individuals examined ... in the absence of a positive control and questions regarding the sensitivity and specificity of the assay, it is not possible to assign a negative predictive value to this"
The US corn supply has been monitored for the presence of the Starlink Bt proteins since 2001.
In 2005, aid sent by the UN and the US to Central American nations also contained some StarLink corn. The nations involved, Nicaragua, Honduras, El Salvador and Guatemala refused to accept the aid.
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