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Update on Biotechnology Products and Appplications

Crop and Soil Environmental News, June 1996

Charles Hagedorn
Biotechnology Extension Specialist

USDA Holds National Forum on Bt Resistance

A diverse group of stakeholders recently attended a rare joint meeting called by the US Department of Agriculture (USDA) to try to forestall the loss of the nation's most valuable biological insecticide. In April, 1996, more than 120 scientists, farmers, environmentalists, consumers, and pesticide and biotechnology company representatives attended a National Forum on Insect Resistance to Bacillus thuringiensis (Bt) to discuss the problem of pest resistance to Bt insecticides. Scientists invited to speak at the forum agreed that the commercialization of transgenic Bt crops threatens the usefulness of Bt, a natural pesticide produced by the soil bacterium Bacillus thuringiensis. Unless steps are taken to properly manage Bt crops, insects are likely to develop resistance quickly. Bt corn, cotton, and potato have already been approved for planting in the current growing season. Conference participants emphasized that organic and sustainable farmers and integrated pest management practitioners who depend on Bt spray formulations to control insects will lose a valuable tool if resistance develops. Bt has been used in spray form for decades against a number of economically important insect pests and is generally presumed as safe to mammals and other nontarget organisms. Despite the critical need for effective resistance management plans to delay resistance, the forum made clear that companies lack the scientific data essential to constructing effective Bt resistance management plans. The plans currently being implemented for Bt corn, cotton, and potato are based primarily on experience with other insect control agents and may or may not be suitable for Bt. The USDA plans to publish a report on the forum's findings and recommendations later this year.

First Proposed Release of Transgenic Nematode

In late winter, the USDA received a request for review of the first proposed environmental release of a genetically engineered nematode. Although both USDA and EPA acknowledge that they lack the authority to regulate this transgenic organism, USDA has agreed to give the proposed test an unofficial review. Nematodes are a group of tiny animals, round worms, which are widely distributed in a range of habitats. Classified into thousands of different species, some live freely in soil or water while others are parasites of humans, animals, and plants. A Rutgers University scientist proposes to test an engineered nematode Heterorhabditis bacteriophora, a parasite of insects, that contains genes from two unrelated organisms, a jellyfish and another nematode. The purpose of the test is to determine the effects of the new genes on the nematode's persistence under field conditions. Ultimately, the scientist wants to use genetic engineering to enable the nematode to last longer in the field so that it can replace chemical insecticides in integrated pest management systems.

The transgenic nematode differs from its nonengineered counterpart in two important respects. First, the florescence gene from jellyfish causes the nematode to appear green rather than colorless in the presence of blue light. This color change allows for rapid screening of soil samples to detect the transgenic nematode. Second, the engineered nematode is more tolerant of heat shocks than the nonengineered form, since multiple copies of a heat shock protein gene from another nematode (Caenorhabditis elegans, a free-living soil nematode) confer greater tolerance to a sudden shock of high temperature. The researcher hopes that enhanced heat tolerance will translate into greater persistence in the field. The Rutgers application indicates that the nematodes engineered with multiple gene copies were 18 times more tolerant of heat shocks than nonengineered forms. This proposed test reveals one of the major gaps in the federal regulatory framework for biotechnology, the lack of oversight of most genetically engineered invertebrates. Invertebrates are animals, such as worms, sponges, and insects, that lack a backbone.

Gene Transfer in Engineered Canola

Danish scientists have recently shown that herbicide-tolerance genes from engineered oilseed rape (canola) became established in weedy populations after just two generations of interbreeding. The results showed for the first time that genes from transgenic crops could become established quickly in weedy populations. In the study, canola plants that had been engineered with an herbicide-tolerance gene to make it resistant to the herbicide were allowed to interbreed naturally in field experiments with weedy wild mustard relatives. Many of the hybrids produced by the crop/weed interbreeding turned out to be herbicide tolerant, that is, they carried the herbicide-tolerance gene from the engineered crop. The scientists then bred some of the transgenic herbicide-tolerant hybrids with weedy relatives in what is called a backcross. The backcross produced many herbicide-tolerant plants that closely resembled the wild, weedy parents. In other words, just two generations of interbreeding produced herbicide-tolerant weeds, and these weeds could resist the same herbicide to which the crop was tolerant-obviously creating a weed control problem for farmers growing the herbicide-tolerant crop.

Scientists have disagreed on the seriousness of the risk of moving genes into wild, weedy relatives. Ecologists have long predicted that transgenes could become established in wild populations and that some of the new genes in wild populations may have ecological impacts, just as the Danish study showed. But some scientists have suggested that the risk would be minimal because crosses between genetically engineered crops and weeds would produce hybrids too weak and infertile for further interbreeding. Unable to get over the barrier presented by the weak hybrids, the new genes would have trouble moving into wild populations. This study shows that at least in one case the hybrids were no barrier at all.

Allergenic Concerns with Engineered Soybeans

A recent study in the medical literature reported that an allergen transferred from Brazil nut to soybean by genetic engineering retained its allergenic properties and caused a reaction to the serum of people sensitive to Brazil nut. This result confirms another predicted risk of genetic engineering: that foods previously safe to eat may become dangerous as a result of the transfer of allergenic proteins. Allergic reactions are immune system responses to substances that most other people tolerate. Food allergies cause reactions ranging from mild, such as erratic heart beats, to serious, such as seizures and even death.

The medical study was undertaken after Pioneer Hi-Bred, a seed company, began developing a transgenic soybean containing a new protein from Brazil nut. The protein was being added to the soybean to improve its nutritional makeup. The Brazil nut protein is rich in methionine, an amino acid essential in human and animal nutrition. When blood serum from persons allergic to Brazil nut was tested against engineered soybeans and Brazil nut, the reactions were the same, indicating that the engineered soybean contained the Brazil nut allergen. Nonengineered soybeans did not react with the blood serum. On skin-prick testing, three people allergic to nuts reacted positively to engineered soybean extracts containing the Brazil nut protein but negatively with nonengineered soybeans. The experimenters decided not to do feeding tests with the transgenic soybean because the allergic persons reacted to Brazil nuts with moderate to severe allergy reactions. Once Pioneer Hi-Bred learned of the allergenicity of the transgenic soybean, the company decided not to market the product.

First Release of an Engineered Arthropod

In late February USDA approved the first field test of a genetically engineered arthropod, a mite that feeds on other mites. The approval cleared the way for a University of Florida entomologist to release about 1400 transgenic mites on bean plants in a small research plot in Florida's Alachua County. The mite was engineered to contain a bacterial gene that acts as a marker to make it easy for researchers to track the mite in the environment. Using the new marker, scientists will monitor the transgenic mite's ability to control spider mites under field conditions. USDA's approval came despite recommendations from over 30 environmental, citizen, and public interest groups that the test be delayed pending full public participation in the risk review process and a public discussion of the risks associated with engineered arthropods. Instead, the USDA chose to move quickly to approve the test without officially informing the public or soliciting public comment. The negative publicity and controversy generated by this test in Florida is an indicator that the public is not yet ready to be left out of the biotechnology approval process.

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