CASE STUDY B.t. corn - Mais B.t.

Bt-corn is a type of genetically modified organism, termed GMO. A GMO is a plant or animal that has been genetically modified through the addition of a small amount of genetic material from other organisms through molecular techniques. Currently, the GMOs on the market today have been given genetic traits to provide protection from pests, tolerance to pesticides, or improve its quality. Examples of GMO field crops include Bt-potatoes, Bt-corn, Bt-sweet corn, Roundup Ready soybeans, Roundup Ready Corn, and Liberty Link corn.

Genetically modified foods are foods derived from GMO crops. For example, corn produced through biotechnology is being used in many familiar foods, including corn meal and tortilla chips. In addition, corn is used to make high fructose corn syrup, which is used as a sweetener in many foods such as soft drinks and baked goods. While the FDA (U.S. Food and Drug Administration) regulates genetically modified foods, it considers Bt-corn to be nutritionally equivalent to traditional corn.

To transform a plant into a GMO plant, the gene that produces a genetic trait of interest is identified and separated from the rest of the genetic material from a donor organism. Most organisms have thousands of genes, a single gene represents only a tiny fraction of the total genetic makeup of an organism.

non modifie-------------------------modifie

A donor organism may be a bacterium, fungus or even another plant. In the case of Bt corn, the donor organism is a naturally occurring soil bacterium, Bacillus thuringiensis, and the gene of interest produces a protein that kills Lepidoptera larvae, in particular, European corn borer. This protein is called the Bt delta endotoxin. Growers use Bt corn as an alternative to spraying insecticides for control of European and southwestern corn borer.

Bt Delta Endotoxin

The Bt delta endotoxin was selected because it is highly effective at controlling Lepidoptera larvae, caterpillars. It is during the larval stage when most of the damage by European corn borer occurs. The protein is very selective, generally not harming insects in other orders (such as beetles, flies, bees and wasps). For this reason, GMOs that have the Bt gene are compatible with biological control programs because they harm insect predators and parasitoids much less than broad-spectrum insecticides. The Bt endotoxin is considered safe for humans, other mammals, fish, birds, and the environment because of its selectivity. Bt has been available as a commercial microbial insecticide since the 1960s and is sold under many trade names. These products have an excellent safety record and can be used on many crops until the day of harvest.

To kill a susceptible insect, a part of the plant that contains the Bt protein (not all parts of the plant necessarily contain the protein in equal concentrations) must be ingested. Within minutes, the protein binds to the gut wall and the insect stops feeding. Within hours, the gut wall breaks down and normal gut bacteria invade the body cavity. The insect dies of septicaemia as bacteria multiply in the blood. Even among Lepidoptera larvae, species differ in sensitivity to the Bt protein.

 

Genetic Modification

Do Bt-corn hybrids differ only in that they possess the genetic code to produce the Bt protein? Not exactly. To add a trait to a crop plant, the gene must be inserted along with some additional genetic material. This additional genetic material includes a promoter sequence that, in part, determines how the new trait is expressed in the plant. For example, the promoter may cause to protein to be expressed in certain parts of the plants or only during a particular period of time. There is a marker gene that allows plant breeders to easily determine which plants have been transformed. Herbicide and antibiotic tolerance promoters are commonly used to identify transformed plants. There may also be a plasmid or vector sequence that allows for rapid multiplication of the gene of interest in a bacterial host prior to insertion in the crop plant.

FDA Approval

Federal food law requires premarket approval for food additives, whether or not they are the products of biotechnology. FDA treats substances added to food products through recombinant DNA techniques as food additives if they are significantly different in structure, function or amount than substances currently found in food.

However, if a new food product developed through biotechnology does not contain substances that are significantly different from those already in the diet, it does not require premarket approval. Products that are genetically engineered to provide pesticide traits, such as resistance to the corn borer, are also subject to regulation by the Environmental Protection Agency. Currently, genetically modified foods in the United States do not require special labeling to notify consumers.

CONTRE OGM- hasards environnementaux

---Unintended harm to other organisms---

 Pollen from B.t. corn cause high mortality rates in monarch butterfly caterpillars. Monarch caterpillars consume milkweed plants, not corn, but the fear is that if pollen from B.t. corn is blown by the wind onto milkweed plants in neighboring fields, the caterpillars could eat the pollen and perish. Although the Nature study was not conducted under natural field conditions, the results seemed to support this viewpoint. Unfortunately, B.t. toxins kill many species of insect larvae indiscriminately; it is not possible to design a B.t. toxin that would only kill crop-damaging pests and remain harmless to all other insects. This study is being reexamined by the USDA, the U.S. Environmental Protection Agency (EPA) and other non-government research groups, and preliminary data from new studies suggests that the original study may have been flawed. This topic is the subject of acrimonious debate, and both sides of the argument are defending their data vigorously. Currently, there is no agreement about the results of these studies, and the potential risk of harm to non-target organisms will need to be evaluated further.

---Reduced effectiveness of pesticides---

 Just as some populations of mosquitoes developed resistance to the now-banned pesticide DDT, many people are concerned that insects will become resistant to B.t. or other crops that have been genetically-modified to produce their own pesticides.

---Gene transfer to non-target species---

 Another concern is that crop plants engineered for herbicide tolerance and weeds will cross-breed, resulting in the transfer of the herbicide resistance genes from the crops into the weeds. These "superweeds" would then be herbicide tolerant as well. Other introduced genes may cross over into non-modified crops planted next to GM crops. The possibility of interbreeding is shown by the defense of farmers against lawsuits filed by Monsanto. The company has filed patent infringement lawsuits against farmers who may have harvested GM crops. Monsanto claims that the farmers obtained Monsanto-licensed GM seeds from an unknown source and did not pay royalties to Monsanto. The farmers claim that their unmodified crops were cross-pollinated from someone else's GM crops planted a field or two away. More investigation is needed to resolve this issue.

---Sollution---
There are several possible solutions to the three problems mentioned above. Genes are exchanged between plants via pollen. Two ways to ensure that non-target species will not receive introduced genes from GM plants are to create GM plants that are male sterile (do not produce pollen) or to modify the GM plant so that the pollen does not contain the introduced gene. Cross-pollination would not occur, and if harmless insects such as monarch caterpillars were to eat pollen from GM plants, the caterpillars would survive.
Another possible solution is to create buffer zones around fields of GM crops. For example, non-GM corn would be planted to surround a field of B.t. GM corn, and the non-GM corn would not be harvested. Beneficial or harmless insects would have a refuge in the non-GM corn, and insect pests could be allowed to destroy the non-GM corn and would not develop resistance to B.t. pesticides. Gene transfer to weeds and other crops would not occur because the wind-blown pollen would not travel beyond the buffer zone. Estimates of the necessary width of buffer zones range from 6 meters to 30 meters or more. This planting method may not be feasible if too much acreage is required for the buffer zones.