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 naïve 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.

UPDATE: POTENTIAL IMPACTS OF POLLEN FROM Bt CORN

Scientists convened in Chicago on November 2 to share preliminary results of research conducted last summer on the possible effects of genetically engineered Bt corn on the monarch butterfly.

The Bt toxin found in Bt corn is active against the Lepidoptera family of moths and butterflies, including the monarch butterfly. However, when Bt corn was approved in the US and Canada, regulators and scientists reasoned that the impact of Bt corn—or more correctly the pollen from Bt corn containing active toxin—on monarch populations would be minimal. This is because milkweed, the desired food of monarch larvae, is rarely found in corn fields, but in adjacent fields, and the toxin is rapidly inactivated by ultraviolet light and drought conditions. They further reasoned that non-discriminate spraying for other corn pests may present a significantly higher risk to the monarch population through chemical drift.

In May 1999, a study by Cornell University researchers published in the journal Nature (1) indicated that pollen from Bt corn could kill monarch caterpillars in laboratory tests. The authors correctly recognized that the study was limited in applicability, and that field tests would be required to determine the significance of this finding in an artificial environment. Upon publication, Dr. John Losey was quoted as saying, "We can't forget that Bt corn and other transgenic crops have a huge potential for reducing pesticide use and increasing yields. This study is just the first step, we need to do more research and then objectively weigh the risks versus the benefits of this new technology."

In response to the Cornell report, a consortium of biotechnology and pesticide companies —the Agricultural Biotechnology Stewardship Working Group—funded 17 studies to quantify the risk of Bt corn to monarchs. The research was conducted during the summer of 1999 at universities in corn-producing regions of North America. Data presented at the meeting indicated that not all strains of Bt corn are equally toxic (2); some varieties of Bt corn may, in a theoretical or laboratory setting, harm the butterfly, while other types may not (3). Furthermore, it was suggested that the amount of pollen migrating to milkweeds was "likely to be dangerous to only those monarchs feeding on milkweeds within or close to the edges of the cornfields" (2).

Mark Sears, chair of the Department of Environmental Biology at the University of Guelph and chair of the Ontario Corn Borer Coalition, reported that virtually all pollen grains land within ten yards of the field, 90 per cent of which travel less than five yards (4). Sears postulated that the risk to monarch larvae is minimal, especially after discovering that at least 500 grains of pollen per square centimeter of milkweed leaf were necessary to sicken caterpillars. After three days of accumulation during pollination season, Sears found this concentration was barely attained on nearby milkweed leaves.

Iowa State University's John Pleasants found that wind direction, rainfall, and other factors significantly affect pollen concentrations on milkweed. He reported that, "Eighty-eight percent of milkweed within one meter of a corn field would fall below the level where they could hurt the caterpillars and 100 percent of the milkweed just two meters from a Bt field would be monarch-safe" (5). Such findings on pollen dispersion are especially significant when coupled with planting preferences. Powell et al. (6) found that planting the borders of a corn field to non-Bt corn was the second most prevalent implementation of Bt-refugia guidelines among 400 Ontario corn producers who planted Bt-corn in 1999, and the most common practice among those with more than 100 acres of corn.

Brower and Zalucki (2) identified key areas needing further investigation. The effects of Bt corn on monarch butterflies will depend on distribution and abundance of milkweed within and around the edges of corn fields, oviposition on the milkweeds, and temporal coincidence between susceptible monarch life stages and pollen shedding of the corn crop. Review of data indicated basic monarch biology and ecology were poorly understood, and data from toxicity bioassays were too preliminary to draw any conclusions. Brower and Zalucki encouraged researchers to conduct field research during the summer of 2000, exposing cohorts of monarchs to pollen on field plants within corn fields using various Bt strains and non-Bt corn and wild controls. Toxic and chronic effects of Bt also need to be determined.

Sources

1. Losey JJ, Raynor L, and Cater ME 1999. Transgenic pollen harms monarch larvae. Nature 399: 214

2. Brower LP and Zalucki MP. 1999. Bt-corn and its effects on Monarch butterflies: A note of caution. November 11. e-mail listserve.

3. Currie BM 1999. Altered corn-butterflies. Associated Press, November 3.

4. Weiss R. 1999. Gene-altered corn's impact reassessed; studies funded by biotech consortium find little risk to monarch butterflies. The Washington Post, November 3: A3.

5. Kendall P. 1999. Monarch butterfly so far not imperiled; gene-altered corn gets an early OK in studies. Chicago Tribune, November 2: p 4.

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.

GENE FLOW BETWEEN CULTIVATED AND WILD BEET

The genetic modification of crops has drawn criticism from opponents who contend that gene flow from these crops may endanger wild populations of sexually compatible weedy relatives. In a study published recently in Molecular Ecology, Detlef Bartsch and Norman Ellstrand have reported the feasibility of gene flow between cultivated and wild beet (1). Their model for this study was Beta vulgaris, a species that includes internationally grown crops of red beet, sugar beet, and Swiss chard.

Beet has been grown since the third century AD, but had not been cultivated into domesticated varieties until the 1800's in Germany and France. Cultivated varieties of beet in the Chenopodiaceae family are grown widely for human consumption, the production of sugar, and for livestock fodder. The family is also noted for containing many invasive weed species affecting agricultural fields.

To show the impact of gene flow from cultivated to wild populations, Bartsch and Ellstrand tracked the frequency of isozyme alleles commonly found in cultivated Beta vulgaris and in the wildtype sea beet (B. maritima). They studied agricultural conditions in which naturally occurring weedy relatives are grown near stands of the cultivated crop.

Ellstrand's group quantified isozyme alleles specific to the cultivated beet. These alleles appeared in high frequencies in the 26 study accessions of the crops. Although isozyme genes are rarely found in wild sea beet populations, the 20 sea beet accessions growing near cultivated beet varieties contained isozyme alleles at a level characteristic of that found in cultivated plants. These gene frequencies were not found in the 19 sea beet accessions growing in isolation from the cultivated beet crops.

The Bartsch, Clegg, and Ellstrand research team has conducted extensive studies on beet genetic divergence using allozyme analysis, as well as gene flow studies of other crop plants. Although this study did not show the direct transmission of the genes from the cultivated crop to the wild plants, it supports a 1992 study by S. Santoni and A. Berville that reported the successful sexual reproduction between cultivated and wild beet (2). At the conclusion of their study, Santoni and Berville warned that sexual compatibility could likely be a possible mechanism of gene transmission between transgenic and wild beet. Similarly, a 1998 study indicated that isozyme variations most likely occur by gene exchange and not random variation (3).

Bartsch and Ellstrand suggest that gene flow is a potentially important driving force in plant evolution, and their research demonstrates gene flow rates that are higher than previously anticipated between different populations of plants. They are concerned about the evolutionary consequences of gene hybridization between crops and wild relatives. Their concerns echo those expressed by K. Morgan and C. Strobeck in their 1979 paper in Nature in which they identified many of the issues associated with intragenic recombination and the genetic stability of natural populations (4).

Gene flow from GM crops is important because of the possibility that novel genes could have deleterious effects on the wild plant populations. However, a century of conventional gene flow has had no adverse effect on the genetic diversity of wild sea beet populations in Italy. The impact of transgenic gene flow will depend on the ecological advantage of the trait. As recently demonstrated by Bartsch and his collaborators, transgenically introduced resistance to a serious viral disease called Rizomania in cultivated beet will have no adverse effect on wild sea beet populations, because the virus is not present in this group (5). The effect of other fitness enhancing traits on wild beet populations may differ, but it is absolutely case dependent.

Recently, the beet has received much publicity because of the development of the GM sugar-free beet (genetically modified to convert sucrose to fructan) in the Netherlands, and Monsanto's high-sucrose beet. GM beet field trial sites have been the target of vandalism in 1995 and 1996 in Germany, and 1997 and 1998, respectively, in Ireland and England. A glyphosate-tolerant sugar beet has recently been deregulated in the US as well. GM technology opponents are using scientific findings, such as the Bartsch and Ellstrand study, to legally combat the release of GM crops.

Sources

1. Bartsch D, Lehnen M, Clegg J, Pohl-Orf M, Schuphan I, and Ellstrand NC. 1999. Impact of gene flow from cultivated beet on genetic diversity of wild sea beet populations. Molecular Ecology 8(11):1733-1741.

2. Santoni S and Berville A. 1992. Extramarital sex amongst the beets—evidence for gene exchanges between sugar beet (Beta vulgaris L.) and wild beets: Consequences for transgenic sugar beets. Plant Molecular Biology 20(4):578-580.

3. Tufto J, Raybould AF, Hindar K, and Engen S. 1998. Analysis of genetic structure and dispersal patterns in a population of sea beets. Genetics 149(4):1975-1985.

4. Morgan K and Strobeck C. 1979. Is intragenic recombination a factor in the maintenance of genetic variation in natural populations? Nature 227(5696):383-384.

5. Bartsch D, Schmidt M, Pohl-Orf M, Haag C, and Schuphan I. 1996. Competitiveness of transgenic sugar beet resistant to beet necrotic yellow vain virus and potential impact on wild beet populations. Molecular Ecology 5:199-205.

TEACHING PLANTS TO COPE WITH SALT

University of Toronto scientists have isolated a critical gene responsible for salt tolerance in plants that may eventually help them grow crops using salt water. The salt tolerance gene, isolated from the Arabidopsis plant, encodes a transport protein in plant cells whose activity enables plants to grow under highly saline conditions.

Salinity is a major abiotic stress limiting the productivity of crop plants around the world, especially under irrigated conditions. Rice soils, which are mostly irrigated, are declining in productivity in many Asian countries because of increasing salinity levels. It is estimated that 25 million hectares (62 million acres) of agricultural land in the world suffers from excess salinization, and another two million hectares of salinated land are added each year.

The presence of excess salt in soil is doubly harmful for plants: salt increases osmotic pressure in plant tissues, resulting in water stress; and sodium ions harm plant cells directly by interfering with plant metabolism. Ensuring an increase in agricultural productivity, especially in the developing countries, hinges on the capacity to sustain crop production on marginal lands afflicted with salinity and water stress factors.