December 2006

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Phillip Jones

In August, the US Department of Agriculture revealed that allotments of conventional long grain rice harbored trace amounts of LL601, a genetically engineered (GE) rice. US rice growers soon found their international markets sheltered behind trade barriers. The unpeaceful coexistence of LL601 in conventional rice shipments exposed the continuing need to isolate agricultural products.

Segregation of produce by its manner of production represents a relatively new development in an industry that traditionally handled fungible fruits, vegetables, and grain. Now, GE crops must be separated from conventional crops to minimize the risk of contamination from pollen drift. GE and conventional crop products must be separated from the products of organic farming during processing and transport. Otherwise, produce loses its market distinctiveness, growers lose money, and lawsuits ensue.

How can the industry achieve a peaceful coexistence of GE, conventional, and organic technologies? The National Association of State Departments of Agriculture (NASDA) and the Pew Initiative on Food and Biotechnology recently published their report of a 2006 workshop that explored this question. Organizers described "peaceful coexistence" as the "ability of conventional, GE and organic growers to effectively meet the specifications of their targeted and consumer markets and ensure a strong, vibrant, diverse agricultural economy." Representatives from industry, the government, and academia offered their views on possible tactics to advance coexistence peacefully.

Good Fences Make Good Neighbors
Many workshop participants focused on the need to isolate GE crops from conventional crops in the United States. The inconsistent rules of international markets drive this seclusion of GE crops and their products. In the EU, food products – conventional or organic – that contain more than 0.9 percent GE material trigger a requirement that the food must be labeled as genetically engineered. Australia, New Zealand, and Brazil have thresholds of one percent, whereas Japan has a more generous five percent threshold. If a conventional or organic product contains sufficient GE material to require a GE label, then it may fatally lose its appeal for the intended market.

During the workshop, Dr. Nicholas Hether, who previously worked as Gerber Products’ Director of Product Safety and Regulatory Sciences, supplied Gerber’s views on GE food. He stressed that the company views GE crops as safe, but it wants to remove itself from the GE food debate and from potential problems in foreign markets. To evade controversy, the company avoids GE ingredients and meets the EU threshold for the presence of GE material. Gerber uses identity-preserved, non-GE sources of crops that have GE varieties.

Mike Gumina, Vice President of Supply Management at Pioneer Hi-Bred International, offered views from the American seed trade. Since the USDA and the US Food and Drug Administration rigorously test GE products, coexistence is not a safety issue, he said. Rather, coexistence is an economic issue, one that raises questions about contracts, politics and the market. Who has the obligation to ensure that agricultural products meet market standards? Growers and others in the production chain bear that responsibility, Gumina said, not the neighbors of those growers. Pioneer takes the responsibility for isolating its crops – GE or conventional – at its expense.

Bryan Endres also looked at the question of who has the duty to ensure a peaceful coexistence. Endres, an Assistant Professor of Agricultural Law at the University of Illinois, Urbana-Champaign, finds a parallel with the fence-in/fence-out cattle debate. In the eastern US, he said, cattle producers accept that they have the duty to fence in their own livestock. In many places in the West, a cattle producer must fence out neighbors’ livestock that would otherwise wander onto the land.

According to Endres, the fence-in/fence-out question has been answered for US producers of GE, conventional, and organic crops. The US market accepts GE crops, and therefore, conventional and organic farmers must fence out GE material by isolating their crops. A grower of GE crops surrounded by organic farms could present an exceptional case. Here, the GE crop grower might have a duty to fence in the GE crops. He warned that such rules reflect a market solution and that liability determinations await the courts.

In the EU, Endres sees an emerging fence-in solution. Germany, for example, has placed a legal burden on GE growers to isolate their crops with buffer zones.

Wolf-Martin Maier, Counselor for Food Safety, Health, and Consumer Affairs for the European Commission Delegation to the United States, also noted that a GE-free zones movement has gained momentum in Europe, especially in Germany. These zones, he said, should only apply to specific crops. Otherwise, they would be inconsistent with the EC’s recommendation of the principle of subsidiarity, which means to regulate as close to the farm as possible. A general ban on GE organisms in a particular area also would violate the principles of coexistence.

Fostering Peace in the Trenches
Endres suggested how states may promote coexistence within the United States. One possibility would be to form grower districts that could alter fence-in/fence-out duties by creating GE-free zones. States could increase oversight of seed purity by testing seed for GE content, and bring labeling laws in line with international market requirements. States could also audit USDA permits for biopharm crops – GE crops that produce pharmaceuticals or industrial chemicals.

Other workshop participants also raised the perennial hot button topic of biopharming as an extraordinary case of GE crop production. Food processing companies, Hether said, have "a lot of angst" about biopharm crops. Mike Zumwinkle, Cargill’s Director of Government Relations, agreed that food companies have become very concerned about biopharming and believe that the federal government should stringently regulate biopharm crops.

The federal government must provide top level oversight of biopharming. As Endres suggested, however, states may add their own regulatory level.

An Oregon government committee on biopharming recently considered recommendations that ranged from a complete ban of biopharm crops to an unqualified endorsement. The committee opted for a restricted endorsement to support biopharming technology while protecting growers of conventional and organic crops. In the committee’s view, Oregon should not rely on federal review of biopharm crop applications. Rather, federal and state officials should collaborate in reviewing the applications. State directors of agriculture and public health should have veto rights over applications. Only crops not designed for human or animal consumption should be used for biopharming. If food crops are used, they should be grown indoors unless the applicant can demonstrate why outdoor plantings are desirable and safe. These recommendations will guide legislation in the near future.

Can’t We All Just Get Along?
A significant hurdle to peaceful coexistence lies in the political and market tensions between GE crop and organic crop production systems. At the same time, this tension has benefited both, said NASDA’s Bob Ehart. That is, consumers who want to avoid GE crops fuel the upsurge of the organic crop market. On the other hand, the market for GE crops has increased in part, because the existence of a distinct organic market blunts efforts to require the labeling of GE ingredients in foods. A GE food labeling system might have stalled the adoption of GE crops in the United States.

Currently, coexistence efforts focus on methods to keep non-GE crops free of GE material. In the future, farmers who grow high-value GE crops may face the challenge of producing their GE crops with a level of purity free from non-GE material.

Each of the three agricultural production systems, said Ehart, plays an important part in supporting vigorous farm economies. Developing methods that foster peaceful coexistence benefits everyone in agriculture.

A copy of the report, "Peaceful Coexistence," can be obtained from the Pew Initiative website (

Phill Jones

Henry I. Miller and Gregory Conko

The application of recombinant DNA technology, or gene splicing, to agriculture and food production, once highly touted as having huge public health and commercial potential, has been paradoxically disappointing. Although the gains in scientific knowledge have been stunning, commercial returns from two decades of R&D have been meager. Although the cultivation of recombinant DNA-modified crops, first introduced in 1995, now exceeds 100 million acres, and such crops are grown by 7 million farmers in 18 countries, their total cultivation remains but a small fraction of what is possible. Moreover, fully 99 percent of the crops are grown in only six countries—the United States, Argentina, Canada, Brazil, China, and South Africa—and virtually all the worldwide acreage is devoted to only four commodity crops: soybeans, corn, cotton, and canola.

Attempts to expand "agbiotech" to additional crops, genetic traits, and countries have met resistance from the public, activists, and governments. The costs in time and money to negotiate regulatory hurdles make it uneconomical to apply molecular biotechnology to any but the most widely grown crops. Even in the best of circumstances—that is, where no bans or moratoriums are in place and products are able to reach the market—R&D costs are prohibitive. In the United States, for example, the costs of performing a field trial of a recombinant plant are 10 to 20 times that of the same trial with a virtually identical plant that was crafted with conventional techniques, and regulatory expenditures to commercialize a plant can run tens of millions dollars more than for a conventionally modified crop. In other words, regulation imposes a huge punitive tax on a superior technology.

Singled out for scrutiny
At the heart of the problem is the fact that during the past two decades, regulators in the United States and many other countries have created a series of rules specific for products made with recombinant DNA technology. Regulatory policy has consistently treated this technology as though it were inherently risky and in need of unique, intensive oversight and control. This has happened despite the fact that a broad scientific consensus holds that agbiotech is merely an extension, or refinement, of less precise and less predictable technologies that have long been used for similar purposes, and the products of which are generally exempt from case-by-case review. All of the grains, fruits, and vegetables grown commercially in North America, Europe, and elsewhere (with the exception of wild berries and wild mushrooms) come from plants that have been genetically improved by one technique or another. Many of these "classical" techniques for crop improvement, such as wide-cross hybridization and mutation breeding, entail gross and uncharacterized modifications of the genomes of established crop plants and commonly introduce entirely new genes, proteins, secondary metabolites, and other compounds into the food supply.

Nevertheless, regulations in the United States and abroad, which apply only to the products of gene splicing, have hugely inflated R&D costs and have made it difficult to apply the technology to many classes of agricultural products, especially ones with low profit potential, such as noncommodity crops and varieties grown by subsistence farmers. This is unfortunate, because the introduced traits often increase productivity far beyond what is possible with classical methods of genetic modification. Furthermore, many of the recombinant traits that have been introduced commercially are beneficial to the environment. These traits include the ability to grow with lower amounts of agricultural chemicals, water, and fuel, and under conditions that promote the kind of no-till farming that inhibits soil erosion. Perhaps society as a whole would have been better off if, instead of implementing regulation specific to the new biotechnology, governments had approached the products of gene splicing in the same way in which they regulate similar products—pharmaceuticals, pesticides, and new plant varieties—made with older and often less precise and less predictable techniques.

Curiously, the largest agbiotech companies may have risked their own long-term best interests, as well as those of consumers, by lobbying for stringent government regulation in order to procure short-term economic advantages. From the earliest stages of the agbiotech industry, regulations acted as a type of governmental stamp of approval for biotechnology products, while the time and expense engendered by overregulation acted as a barrier to market entry by smaller competitors. A ripple effect of overly restrictive regulations is that they reinforce the idea that there is something uniquely worrisome and risky about the use of recombinant DNA techniques. Many companies have had to abandon potentially excellent products because of regulatory obstacles.

Another manifestation of the unfavorable and costly regulatory milieu is the sharp decline in efforts to apply recombinant DNA technology to fruits and vegetables, the markets for which are minuscule compared to commodity crops such as corn and soybeans. Consequently, the number of field trials in the United States involving gene-spliced horticulture crops plunged from approximately 120 in 1999 to about 20 in 2003.

Setting matters aright
The public policy miasma that exists today is severe, worsening, and seemingly intractable, but it was by no means inevitable. In fact, it was wholly unnecessary. From the advent of the first recombinant DNA-modified microorganisms and plants a quarter century ago, the path to rational policy was not at all obscure. The use of molecular techniques for genetic modification is no more than the most recent step on a continuum that includes the application of far less precise and predictable techniques for genetic improvement. It is the combination of phenotype and use that determines the risk of agricultural plants, not the process or breeding techniques used to develop them. Conventional risk analysis, supplemented with assessments specific to the new biotechnology in those rare instances where they were needed, could easily have been adapted to craft regulation that was risk-based and scientifically defensible. Instead, most governments defined the scope of biosafety regulations to capture all recombinant organisms but practically none developed with classical methods.

An absolutely essential feature of genuine reform must be the replacement of process-oriented regulatory triggers with risk-based approaches. In January 2004, the U.S. Department of Agriculture (USDA) announced that it would begin a formal reassessment of its regulations for gene-spliced plants. One area for investigation will include the feasibility of exempting "low-risk" organisms from the permitting requirements, leading some observers to hope that much needed reform may be on the horizon. However, regulatory reform must include more than a simple carve-out for narrowly defined classes of low-risk recombinant organisms. An absolutely essential feature of genuine reform must be the replacement of process-oriented regulatory triggers with risk-based approaches. Just because recombinant DNA techniques are involved does not mean that a field trial or commercial product should be subjected to case-by-case review. In fact, the introduction of a risk-based approach to regulation is hardly a stretch; it would merely represent conformity to the federal government’s official policy, articulated in a 1992 announcement from the White House Office of Science and Technology Policy, which calls for "a risk-based, scientifically sound approach to the oversight of planned introductions of biotechnology products into the environment that focuses on the characteristics of the . . . product and the environment into which it is being introduced, not the process by which the product is created." One such regulatory approach has already been proposed by academics. It is, ironically, based on the well-established model of the USDA’s own plant quarantine regulations for nonrecombinant organisms. Almost a decade ago, the Stanford University Project on Regulation of Agricultural Introductions crafted a widely applicable regulatory model for the field testing of any organism, whatever the method employed in its construction. It is a refinement of the "yes or no" approach of national quarantine systems, including the USDA’s Plant Pest Act regulations; under these older regimens, a plant that a researcher might wish to introduce into the field is either on the proscribed list of plant pests, and therefore requires a permit, or it is exempt. The Stanford model takes a similar, though more stratified, approach to field trials of plants, and it is based on the ability of experts to assign organisms to one of several risk categories. It closely resembles the approach taken in the federal government’s handbook on laboratory safety, which specifies the procedures and equipment that are appropriate for research with microorganisms, including the most dangerous pathogens known. Panels of scientists had stratified these microorganisms into risk categories, and the higher the risk, the more stringent the procedures and isolation requirements.

Strategies for action
Rehabilitating agbiotech will be a long row to hoe. In order to move ahead, several concrete strategies can help to reverse the deteriorating state of public policy toward agricultural biotechnology.

First, individual scientists should participate more in the public dialogue on policy issues. They should demand that policy be rational instead of insisting primarily on transparency or predictability. Some scientists appear convinced that a little excess regulation will assuage public anxiety and neutralize activists’ alarmist messages. Although defenders of excessive regulation have made those claims for decades, the public and activists remain unappeased and technology continues to be shackled.

Scientists are especially well qualified to expose unscientific arguments and should do so in every possible way and forum, including writing scientific and popular articles, agreeing to be interviewed by journalists, and serving on advisory panels at government agencies. Scientists with mainstream views have a particular obligation to debunk the claims of their few rogue colleagues, whose declarations that the sky is falling receive far too much attention.

Second, groups of scientists—professional associations, faculties, academies, and journal editorial boards—should do much more to point out the flaws in current and proposed policies. For example, scientific societies could include symposia on public policy in their conferences and offer to advise government bodies and the news media.

Third, reporters and their editors can do a great deal to explain policy issues related to science. But in the interest of "balance," the news media often give equal weight to all of the views on an issue, even if some of them have been discredited. All viewpoints are not created equal, and not every issue has "two sides." Journalists need to distinguish between honest disagreement among experts, on the one hand, and unsubstantiated extremism or propaganda, on the other. They also must be conscious of recombinant DNA technology’s place in the context of overall crop genetic improvement. When writing about the possible risks and benefits of gene-spliced herbicide-tolerant plants, for example, it is appropriate to note that herbicide-tolerant plants have been produced for decades with classical breeding techniques.

Fourth, biotechnology companies should eschew short-term advantage and actively oppose unscientific discriminatory regulations that set dangerous precedents. Companies that passively, sometimes eagerly, accept government oversight triggered simply by the use of recombinant DNA techniques, regardless of the risk of the product, ultimately will find themselves the victims of the law of unintended consequences.

Finally, venture capitalists, consumer groups, patient groups, philanthropists, and others who help to bring scientific discoveries to the marketplace or who benefit from them need to increase their informational activities and advocacy for reform. Their actions could include educational campaigns and support for organizations such as professional associations and think tanks that advocate rational science-based public policy.

The stunted growth of agricultural biotechnology worldwide stands as one of the great societal tragedies of the past quarter century. The nation and the world must find more rational and efficient ways to guarantee the public’s safety while encouraging new discoveries. Science shows the path, and society’s leaders must take us there.

Henry I. Miller ( is a research fellow at Stanford University’s Hoover Institution. Gregory Conko is the director of food safety policy at the Competitive Enterprise Institute. This article is derived from their book The Frankenfood Myth: How Protest and Politics Threaten the Biotech Revolution (Praeger Publishers, 2004).

Olivier Sanvido, Michèle Stark, Jörg Romeis and Franz Bigler

The global area planted with genetically engineered (GE) crops has consistently increased each year since GE crops were first commercially cultivated in 1996, reaching 90 million hectares in 2005. Five countries (USA, Argentina, Brazil, Canada and China) are growing nearly 95% of the total area of these crops. In contrast the adoption of GE crops in Europe was much less intense. This situation is probably going to change, since the European Union (EU) entered the first GE maize varieties expressing insecticidal proteins from Bacillus thuringiensis (Bt) into the Common EU Catalogue of Varieties in September 2004. It is generally expected that Bt-maize will also be commercially grown in EU countries other than Spain, where commercial GE crop cultivation started in 1998. Several countries such as France, Germany, Portugal, and the Czech Republic started growing Bt-maize in 2005. Compared to Spain, where approximately 12% of the total maize area grown in 2004 (representing 58,000 ha) was planted with Bt-maize, the acreage in these countries is, however, very limited and accounts for less than 1,000 ha each.

GE crops, modern agricultural systems and the environment
Concerns have been raised that the commercial cultivation of GE crops could result in adverse effects on the environment.1 We have therefore reviewed the scientific knowledge on environmental impacts of GE crops deriving from ten years of worldwide experimental field research and commercial cultivation.2 Our study focused on the currently commercially available GE crops that could be relevant for agriculture in Western and Central Europe (i.e., maize, oilseed rape, and soybean), and on the two main GE traits that are currently commercialized, herbicide tolerance (HT) and insect resistance (IR). The sources of information included peer-reviewed scientific journals, scientific books, reports from countries with extensive GE crop cultivation, as well as reports from international organizations.

Potential impacts of GE crops should be put in relation to the environmental impacts of modern agricultural practices that took place during the last decades. Independent from the use of GE crops, modern agricultural systems have profound impacts on all environmental resources, including negative impacts on biodiversity. Several changes in the management of agricultural land over the last century have resulted in a decline in the biodiversity within agro-ecosystems.3,4

Effects of GE crops on non-target organisms
There are concerns that insect-resistant GE crops expressing Cry-proteins from Bacillus thuringiensis (Bt) could harm organisms other than the pest(s) targeted by the toxin. The published large-scale studies in Bt crops assessing possible non-target effects on arthropods have only revealed subtle shifts in the arthropod community, which can be explained by a lack of the target pest resulting from the effective control by the Bt crops.5 No adverse effects on non-target natural enemies resulting from direct toxicity of the expressed Bt toxins have so far been observed in laboratory studies and in the field. There is evidence that the Bt crops grown today are more target-specific and have fewer side effects on non-target organisms than most current insecticides used.

While the adoption of Bt maize has resulted in only modest reductions in insecticide applications due to the small area of conventional maize treated with insecticides against the European Corn Borer, the commercial cultivation of Bt cotton has resulted both in a substantial reduction in quantity and in number of insecticide applications.6 In addition to direct environmental benefits such as fewer non-target effects and reduced pesticide inputs in water, demonstrable health benefits have been documented for farm workers in developing countries due to less chemical insecticide spraying in Bt cotton.7

Impacts of GE crops on soil ecosystems
Similarly to non-target effects above ground, concerns were raised that Bt crops could have effects on soil organisms. Bt toxins enter the soil system primarily via root exudation and via plant remains after harvest. Both degradation and inactivation of the Bt toxin vary, depending on parameters such as temperature and soil type. The initial degradation of the toxin is rapid, while a low percentage (< 2%) may remain in the soil ecosystem following one growing season. Bt toxins have been shown to bind to clay and humic acid compounds; however, no accumulation of toxins has been observed after several years of cultivation of Bt crops.

Population sizes and community structure of soil organisms are subject to both natural seasonal variation and to variations caused by the agricultural system (soil type, plant age, crops, cultivars, and crop rotation). Neither laboratory nor field studies have shown lethal or sublethal effects of Bt toxins on nontarget soil organisms such as earthworms, collembola, mites, woodlice, or nematodes. Some differences in total numbers and community structure have been described for microorganisms. The ecological significance of the observed differences is not clear. Because most studies have not assessed the natural variation occurring in agricultural systems, it is generally difficult to establish whether the differences between Bt and non-Bt crops were exceeding this variation. The only study considering natural variation suggests that observed effects lie within this variation and that the differences between conventional cultivars outweigh the observed influences of Bt crops.8

Gene flow from GE crops to wild relatives
There is general scientific agreement that gene flow from GE crops to sexually compatible wild relatives can occur.9 Experimental studies have shown that GE crops are capable of spontaneously mating with wild relatives, however at rates in the order of what would be expected for non-transgenic crops. Few studies have shown that GE herbicide tolerant (GEHT) oilseed rape (Brassica napus) can form F1 hybrids with wild turnip (Brassica rapa) at low frequency under natural conditions. Questions remain whether these transgenes would cause ecologically relevant changes in recipient plant populations. Although there is a low probability that increased weediness due to gene flow could occur, it is unlikely that GEHT weeds would create greater agricultural problems than conventional weeds. Farmers can generally choose among several herbicides for the cultivation of a given crop and they have further a set of options within a crop rotation to control or manage weeds.

In natural habitats, no long-term introgression of transgenes into wild plant populations leading to the extinction of any wild plant taxa has been observed to date. Transgenes conferring herbicide tolerance are unlikely to confer a benefit in natural habitats because these genes are selectively neutral in natural environments, whereas insect resistance genes could increase fitness if pests contribute to the control of natural plant populations.

Invasiveness of GE crops into natural habitats
Despite the concern that GE crops could invade natural habitats, brought up early in the discussion on potential environmental risk related to the release of GE crops, it seems that modern crop varieties generally stay domesticated. There is no evidence at present that the extensive cultivation of GEHT oilseed rape over several years in Western Canada has resulted in a widespread dispersal of volunteer oilseed rape carrying herbicide-tolerance traits. Although one study found triple-herbicide resistant, and another study reported double-herbicide resistant, oilseed rape volunteers in Western Canada, the general lack of reported multiple-resistant volunteers suggests that these volunteers are being controlled by chemical and non-chemical management strategies, and are therefore not an agronomic concern to most farmers. Furthermore, there is currently no evidence that GEHT oilseed rape has become feral and invaded natural habitats.

Impacts of GE crops on pest and weed management
Impacts of GE crops on pest and weed management practices and their potential ecological consequences are usually difficult to assess, because they are generally influenced by many interacting factors and often only show up after an extended period of time. Numerous weed species evolved resistance to a number of herbicides long before the introduction of GEHT crops.10 The experiences available from regions growing GEHT crops on a large scale confirm that the development of herbicide resistances in weeds is not primarily a question of genetic modification, but of the crop- and herbicide management applied by farmers. Despite extensive cultivation of GEHT oilseed rape in Canada, no weed species has so far been observed being tolerant to the herbicides glyphosate and glufosinate. In continuously cultivated GEHT soybeans in the United States, in contrast, many fields have been treated only with glyphosate, which increases the pressure for the selection of resistant biotypes. As a consequence, three years after the introduction of GEHT soybean varieties, glyphosate-resistant horseweed (Conyza canadensis) has been detected. Although farmers have to add another herbicide to glyphosate to control the resistant weed species, there are alternatives to glyphosate for most weed species that are highly effective and provide good flexibility in application timing. There is, however, no question that glyphosate-resistant weeds will increase the costs of weed management for farmers.

The adoption of GEHT crops has allowed the use of a single broad spectrum herbicide that may reduce the need for costly herbicide combinations. Glyphosate and glufosinate are generally considered toxicologically more benign, being in particular less toxic to humans and the environment than many of the herbicides they replace. In addition, the adoption of GEHT crops has often facilitated the change to conservation tillage agriculture. Growers using conservation tillage have reduced their tillage operations, thus preventing soil erosion and soil degradation.

The results of the UK Farm Scale Evaluations (FSE) showed that weed biomass and numbers of some invertebrate groups were reduced under GEHT management in sugar beet and oilseed rape and increased in maize compared with conventional treatments.11 These differences were related to the weed management of both conventional and GEHT systems. Highly effective weed control practices, such as those chosen for the GEHT crops in the FSE, lead to low numbers of weed seeds and insects. Fewer insects and decreased weed seed might reduce the numbers of birds that depend on these insects and seeds as a food source. The FSE assumed no other changes in field management than GEHT crops replacing non-GE varieties. However, other cropping systems such as conservation tillage are possible, resulting in a greater availability of crop residues and weed seeds and, in consequence, improving food supplies for insects, birds, and small mammals.12

The risks GE crops pose for the environment, and especially for biodiversity, have been extensively assessed worldwide during the past ten years of commercial cultivation. Consequently, substantial scientific data on environmental effects of the currently commercialized GE crops is available today, and will further be obtained given that several research programs are underway in a number of countries. The data available so far provide no scientific evidence that the commercial cultivation of GE crops has caused environmental harm. Nevertheless, a number of issues related to the interpretation of scientific data on effects of GE crops on the environment are debated controversially. To a certain extent, this is due to the inherent fact that scientific data is always characterized by uncertainties, and that predictions on potential long-term or cumulative effects are difficult. Uncertainties can either be related to the circumstance that there is not yet a sufficient data basis provided for an assessment of consequences (the "unknown"), or to the fact that the questions posed are out of reach for scientific methods (the "unknowable"). Although some might argue that experience and solid scientific knowledge are still lacking, the debate is generally not purely due to a lack of scientific data, but more to an ambiguous interpretations of what is considered an ecologically relevant effect of GE crops. The interpretation of study results is thereby often challenged by the absence of a defined baseline to evaluate environmental effects of GE crops in the context of modern agricultural systems. There is thus a need to develop scientific criteria to assist regulatory authorities when deciding whether environmental effects of GE crops are considered relevant.

When discussing the risks of GE crops, one has to recognize that the real choice for farmers and consumers is not between a GE technology that may have risks and a completely safe alternative. The real choice is between GE crops and current conventional pest and weed management practices, all possibly having positive and negative outcomes. To ensure that a policy is truly precautionary, one should therefore compare the risk of adopting a technology against the risk of not adopting it.13 We thus believe that both benefits and risks of GE crop systems should be compared with those of current agricultural practices.

We would like to thank the Swiss Expert Committee for Biosafety for major funding of the study.

The study is publicly available on the internet via the following link: (1.1 MB)


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Olivier Sanvido, Michèle Stark, Jörg Romeis and Franz Bigler
Agroscope Reckenholz-Tänikon Research Station ART,
Reckenholzstr. 191, CH-8046 Zurich, Switzerland

Joaquima Messeguer and Enric Melé

Commercial cultivation of genetically engineered (GE) maize in Europe has been well legislated since 2003 (Directive, 2001/18/CE; Regulation (EC), 1829/2003, 1830/2003). In these regulations, the concept of coexistence has been established as 'the principle that farmers should be able to cultivate freely the agricultural crops they choose, be it GE crops, conventional, or organic crops'. All European countries need to develop national strategies to ensure coexistence (Commission Recommendation, 2003), taking into account that the threshold value of 0.9% for labeling GE maize food and feed has been established.

Coexistence can be affected by the adventitious presence of one crop within another, which can arise for a variety of reasons. These include seed impurities, cross-pollination, volunteer presence, and harvesting and storage practices. The adventitious presence of genetically engineered organisms (GEOs) as a result of cross-pollination is one of the factors that needs to be evaluated in different cropping areas, as local climatic conditions may influence the extent of pollen-mediated gene flow. Maize pollen is relatively large and heavy, but it can travel long distances on airflow, when suitable meteorological conditions occur, and therefore cross-pollination will take place to some extent. The rate of cross-pollination between fields depends on pollen viability, synchronization of flowering, and relative concentrations of pollen in donor and receptor plots (for reviews see Treu and Emberlin 2000; Brookes et al., 2004).

Several field trials have been performed to evaluate gene flow from GE to non-GE maize (reviewed in Devos et al., 2005; Brookes et al., 2006). In these trials it has been demonstrated that when a neighboring non-GE field is at least 1 ha in size, an isolation distance of 20 – 25 m is sufficient to ensure purity levels in harvest material below the 0.9% threshold. It has also been demonstrated that a buffer zone (some maize rows) is more effective than an empty gap (Pla et al., 2006).

In general, field trials were designed by planting a nucleus of maize (GE or a cultivar with a special phenotypic trait) and then studying the occurrence of cross-fertilization in an adjacent field. In most trials, both genotypes had been sown at the same time to increase synchronicity of flowering, in order to detect cross-fertilization in the worst situation that could be found in an area in which GE and non-GE maize coexist. However, could these results be applied to real situations of coexistence? To answer this question a study has been published recently (Messeguer et al., 2006) to elucidate to what extent the results encountered in these field trials can be applied to real situations of coexistence in which GE and non-GE maize fields are sown with different cultivars, with different sowing dates, mixed with other crops, and with different barriers that may influence pollen dissemination.

To perform this study, two crop regions located in Catalunya (Spain) were chosen during the 2004 growing season in which irrigated transgenic Bt (resistant to the corn borer attack) and conventional maize fields coexisted with other crops. Both regions are characterized by small size of the fields (0.5–5 ha, with a mean of about 2 ha). In both regions, two areas were defined: the central area in which conventional fields were selected for sampling; and the surrounding area that may influence rate of pollen-mediated gene flow. The total surface area studied in Térmens was 300 ha, with a central area of 43 ha; whereas in Pla de Foixà the area was 400 ha, with a central area of 100 ha. An aerial view of some fields from Foixà area is shown in Figure l. The different crops (cereals, fruit trees, maize, etc.) were identified during the cropping season, and data on maize cultivar, sowing and flowering dates, and wind speed and orientation were recorded. All of these data were used to choose the non-transgenic fields for sampling. At harvest, samples were collected and analyzed by real-time quantification system-polymerase chain reaction (RTQ-PCR) as described in Pla et al., 2006.

Five conventional fields in the Térmens area and seven in the Foixà area were chosen to detect and quantify the rate of cross-fertilization. In the Térmens area, fields were analyzed for both Mon810 and Bt176 events; whereas, in the Foixà area, analysis was performed for the Mon810 event only, because neither the fields of the selected zone nor the fields of the surrounding zone had been sown with Bt176 maize. A stratified sampling system was applied by dividing fields into different zones according to the distance from the borders. The number of sampling points for each border depended on the size and particular shape of the field. In total 488 analyses were performed.

Values obtained from RTQ-PCR analysis were used to estimate GEO content of the studied fields. All fields were divided into zones by the transects used for sampling and by two virtual lines that follow the field perimeter at 3 or 10 m inside. The partial GEO content of each zone was calculated by averaging four samples that delimited the surface. These values were used to make a graphical representation of the local distribution of adventitious flow in the field (see Figure 2 as an example). The average of these local values, weighted by their corresponding area, was used to obtain a representative estimation of the global field value. In general, the distribution of the GEO content was not uniform in the field, showing some affected areas and providing useful information about the putative pollen donors. In general, the rate of cross-fertilization was higher in borders and decreased towards the center of the field. Nine of the 12 analyzed fields gave values much lower than 0.9%; whereas, in the other three, the values were higher than 0.9%.

To identify which transgenic fields influence the adventitious presence of Bt maize in a conventional field and to what extent, we used an empirical ECP (estimated cross-pollination) index for each pair of transgenic and non-transgenic fields. This index takes into account only two scalar factors—synchronicity of flowering and distance between the fields—that are independent of orientation. In the ECP index, it is assumed that adventitious pollination is directly proportional to the number of days of synchronous flowering and inversely proportional to the square of the distance. High values of this index indicate a significant contribution to adventitious presence of transgenic maize detected in the non-transgenic field. So, with this criterion, we were easily able to visualize and classify the fields most responsible for the adventitious flow detected. Figure 2 shows one of the analyzed fields where Bt fields a, b, c, and d could influence its GEO content due to pollen mediated gene flow. Moreover, for each individual field studied, a global index (GI) was calculated by adding ECP indices of surrounding transgenic fields, giving an estimation of global gene flow produced, considering only distance and synchronicity of flowering.

A good correlation (R2 = 0.9491, n = 15) was found between the average percentage of GEO obtained by RTQ-PCR analysis of samples and the GI of the ECP indices, showing that GI may be useful for estimating the percentage of GEO in fields before harvesting.

Data obtained in several field trials especially conducted to quantify the adventitious presence of GEOs have been used to predict the separation distance between transgenic and non-transgenic fields that needs to be established to ensure coexistence. However, almost none of the Bt fields studied in the Foixà and Térmens areas had a separation distance or a buffer zone (recommended by seed producers only for fields larger than 5 ha). Several different situations were encountered, depending on agronomical and physical factors and on the fact that, in the real situation of coexistence, there was competition between the pollen produced by the analyzed field and pollen coming not from one field only, but from several fields both close to and at different distances away from the analyzed field.

Although the reliability of this approach must be confirmed by accurate calculations using mathematical models, we can obtain some idea of the size of the security distance needed to maintain adventitious presence of GEO under the 0.9% threshold required by European Union regulations. The slope of the regression line of GEO content vs. GI is 0.0689, and on the basis of a field surrounded by four transgenic crops with total synchronicity of flowering, the expected value of the GEO content is 2.76% if the distance is within the first 10 m, 0.69% within the second, and 0.30% within the third. This means that a security distance between 10 and 20 m should be sufficient to maintain the GEO content below the 0.9% threshold under the worst circumstances. The studied areas must be considered ‘difficult zones’ for controlling pollen flow, because they are flat and windy, with small fields (2 ha average), and with a high percentage of transgenic content.

Results obtained in this study perfectly match those obtained in field trials specially designed to study pollen mediated gene flow in maize. We have shown that coexistence between GE and conventional fields can be achieved by establishing simple rules that take into account the synchronicity of flowering and distance between fields. Moreover, data collected in this study will be very useful for validation of models to predict pollen flow at landscape level with different spatial distributions (smaller and larger fields).


Brookes G, et al. (2004) Genetically Modified Maize: Pollen Movement and Crop Coexistence. Dorchester, UK: PG Economics Ltd.

Brookes G, et al. (2006) Coexistence of genetically modified and non-genetically modified maize: Making the point on scientific evidence and commercial experience. PG Economics Ltd.

Devos Y, et al. (2005) The coexistence between transgenic and non-transgenic maize in the European Union: a focus on pollen flow and cross-fertilisation. Environmental Biosafety Research 4, 71-87

Messeguer J, et al. (2006) Pollen-mediated gene flow in maize in real situations of coexistence. Plant Biotechnology Journal 4, 633-645

Plà M, et al. (2006). Assessment of real-time PCR based methods for quantification of pollen-mediated gene flow from GM to conventional maize. Transgenic Research 15,219-228

Treu R, and Emberlin J. (2000) Pollen Dispersal in the Crops Maize (Zea mays), Oil Seed Rape (Brassica napus ssp. oleifera), Potatoes (Solanum tuberosum), Sugar Beet (Beta vulgaris ssp. vulgaris) and Wheat (Triticum aestivum). Evidence from Publications. A Report Commissioned by the Soil Association. Worcester: National Pollen Research Unit, University College Worcester.

Joaquima Messeguer & Enric Melé
Consorci CSIC-IRTA. Genètica Vegetal. Cabrils
Ctra de Cabrils Km 2
E-08348 Cabrils (Barcelona) Spain

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