In this article we will discuss about:- 1. GM Crops and Agricultural Intensification 2. Issues Related to GM Crops 3. Risks and Benefits 4. Future Research and Development 5. International Developments.
Contents:
- GM Crops and Agricultural Intensification
- Issues Related to GM Crops
- Risks and Benefits Related to GM Crops
- Future Research and Development of GM Crops
- International Developments for Safety of GM Crops
1. GM Crops and Agricultural Intensification:
The prospect of gene transfer causes concern for crops that have wild relatives in the same geographical area. Perhaps of greater importance is the fact that management of some GM crops would be very different from conventional intensive agriculture or organic farming.
In the USA, GM herbicide-tolerant (GMHT) crops are grown under a regime of broad-spectrum herbicides applied during the growing season. Farmers report almost total weed elimination from GMHT crops, which include cotton, soybean, maize, sugar beet and oil-seed rape. Recent research in the UK confirms that weed control in GM beets and other GMHT crops is likely to become much more efficient. These results are hardly surprising, since this is the main purpose behind the technology.
This GMHT system will soon be available, at least experimentally, for many agricultural crops, including vegetables. Broad-spectrum herbicides used on commercial scale GMHT crops during the growing season may be far more damaging to farmland ecosystems than the selective herbicides they might replace. Using these herbicides in the growing season may also increase the impact of spray drift on to marginal habitats and watercourses.
It is not the volume of herbicides that is the issue but their efficiency and impact on wildlife. When insect resistance and herbicide tolerance are combined in the same crop variety, there may be few insects capable of feeding on the crops and few invertebrates and birds would be able to exploit the weed-free fields.
The use of more effective pesticides (including herbicides) over the past 20 years has been a major factor in causing serious declines in farmland birds, arable wild plants and insects in several European countries. Pesticides not only have direct toxic effects on wildlife but they also enable modern crop-management changes to take place.
Besides the aesthetic and scientific reasons for conserving biodiversity within and around agricultural crops, there is another important utilitarian reason for wanting to do so. There is a danger of losing the food-chain links between native species and crop systems. This link is vital for preserving the function of biodiversity to deliver early warning of dangers in crops or the chemicals used to manage them.
There is some evidence that the use of GM crops with insect resistance in North America is reducing the volume and frequency of pesticide use on cotton, maize and soybean. In addition, the future development of new crops with improved tolerance to abiotic factors (such as drought, salinity, frost) and the advent of ‘pharmed’ crops used to produce vaccines and industrial products may also change crop-management practices. They may either increase or decrease demand for arable land in the long term. They may also put further pressure on natural biodiversity on marginal land.
The problem with assessing the environmental impact of these changes in management is that the regulatory system and the public have little scientific data on which to assess the real risks and potential benefits from adopting GMHT crop systems.
In the UK, 27 field-scale experiments are in place to try to answer some of these important questions. Research is urgently required to make the ecological consequences of using GM crops clearer. Information from such research can then be used by regulators to make more informed and publicly defensible decisions about whether GM crops should be commercialized and under what conditions.
2. Issues Related to GM Crops:
i. Gene Flow and Transfer of Traits to Other Species:
Gene transfer is an issue when crops are being grown in areas close to their wild relatives, with whom they are able to cross to form interspecific hybrids. Natural hybridization occurs within 12 of the world’s 13 most important food crops and their wild relatives (the exception being banana, since cultivated banana is infertile). Thus, the world’s major cereal crops (maize, wheat, barley, and sorghum), oil-seeds (rape-seed, soybean and groundnut) and root and tuber crops (cassava and potato) can cross with their compatible wild relatives.
Such wild relatives occur in the centres of diversity of these crops. Natural hybridization may occur at low frequency when pollen blows or is otherwise transported from crops to wild relatives in the vicinity. Such gene flow and interspecific crosses cannot occur in crops whose centres of origin and diversity and closest wild relatives are on other continents (e.g. maize in Europe, since its centre of origin is in Mexico).
Recent research confirms that genes introduced into some GM crops may spread into related native species. This is not unexpected since genes have long been known to move from conventionally bred crops to wild relatives, at low frequency. For example, in the UK, such hybrids occasionally occur between oil-seed rape and native species, such as wild turnip. Published studies on the gene transfer issue are dominated by rape-seed, whose centre of origin is in Europe.
The difference is that genes inserted into GM crops are often derived from other phyla, giving traits that have not been present in wild plant populations. The concern is that these genes may change the fitness and population dynamics of hybrids formed between native plants and related GM crops, eventually back-crossing genes into the native species. The importance of pollen transfer from GM crops to wild relatives is not that it occurs but whether the resulting hybrids survive and reproduce and introgress genes back into the native population.
The issue is not so much the rate of gene flow (on which there has been much research), as the impact that this might have on agriculture and the environment (on which there has been very little research). Conventional plant breeding, using techniques such as mutagenesis and embryo rescue, also produces new genes in crops, about which we also know very little regarding their behaviour in the wild.
ii. Weediness:
There are risks that GM plants could have negative impacts on natural ecosystems by increasing their weediness by two routes. First, the GM plants could establish self-sustaining populations outside cultivation themselves. The concern is that these plants may become invasive weeds that out-compete wild populations and thus lead to further decreases in biodiversity in native plant habitats. Weeds having tolerance to a range of herbicides could also emerge.
Secondly, novel genes from GM crops could be introduced into their wild relatives by pollen spread and the survival and reproduction of the resulting hybrids. This may have a negative impact on the wild plant population if new genes are introgressed back into the wild plant population. For this to happen, the new genes must increase the plants’ fitness to survive and reproduce in the wild.
Transfer of certain genes, such as resistance to insects, fungi and viruses, may increase the fitness (ability to reproduce) of any resulting hybrids. If hybrids acquired insect resistance from GM crops, they could damage food chains dependent on insects feeding on previously non-toxic wild plants.
Not only would there be a direct effect, for many insects are entirely dependent on single plant species, but acquisition of resistance in wild plants would probably change their population dynamics, increasing the risks of their invading agricultural land and natural ecosystems.
Many geneticists would argue that most ‘foreign’ genes introduced accidentally from GM crops to crop/native plant hybrids would decrease their fitness in the wild, leading to rapid selection of these genes out of the population. A recently published 10-year study by Imperial College in the UK on the fitness of GM plants to survive in the wild supports this hypothesis. GM maize, rape-seed and sugar beet (all with herbicide tolerance) and potato with insect resistance were compared with conventionally bred crops.
All four GM crops were out-competed by their conventionally bred relatives. Thus, in this experiment, the genetic modifications in these species for herbicide tolerance and insect resistance made them less competitive and less fit to survive in the wild. Plant breeding tends to reduce rather than increase the weediness characteristics of crop plants.
iii. Trait Effects:
Trait effects are those that are harmful to non- target organisms. For example, plants modified to produce pesticidal proteins, such as Bt toxins, may have both direct and indirect effects on populations of non-target species. One group of Bt toxins primarily targets Lepidoptera (butterflies and moths, particularly the European corn-borer) and the others affect Coleoptera. The effects of Bt toxin-producing plants on non-pest species among these insect groups may vary widely, depending on sensitivity and the concentration of Bt in transgenic plants and environmental conditions.
Laboratory experiments demonstrated that the larvae of monarch butterflies (a relative of the European corn-borer) were susceptible to pollen from Bt maize when ingested in large amounts, but the actual ecological significance of this laboratory experiment was not clear. Subsequent field experiments in several locations in North America found that there were no significant differences between butterfly survival in areas planted with Bt maize and those planted with conventional crops.
In assessing trait effects, such as those of Bt crops, on non-target species, it is important to compare the potential risks of Bt crops with the present effects of chemical pesticide use in risk assessments.
iv. Genetic and Phenotypic Variability:
This is the tendency of a plant to exhibit unexpected (pleotropic) characteristics in addition to the expected characteristics. This trait is well known from conventional breeding, but becomes an identifiable hazard only if the variability leads to one of the other safety issues, such as greater weediness or a greater tendency for out-crossing.
v. Expression of Genetic Material from Pathogens:
Another potential hazard would be the possibility of recombination of a virus gene expressed by the plant with genes from another virus infecting that plant. This risk would be similar to the risk of genetic re-combinations following mixed virus infections that occur in nature.
Genetic Modification of Native Species:
There is some experimentation on genetic modification of native species. These developments greatly increase the risks of gene transfer because GM native organisms will be completely cross-fertile with native species. There is also a risk that GM varieties of native plants would be fitter than native species and colonize natural ecosystems, with unpredictable results.
Biotechnology and Biodiversity:
Risks to biodiversity and wildlife are important issues in particular environments. Careful assessment is necessary of the risks associated with the creation of new selection pressures coming from the introduction of GIOs into the environment. These new selection pressures may have profound effects on the delicate balance of life.
Of special concern is the potential impact on biodiversity of GIOs as selection pressures wield influence in the species composition of the ecosystem. These concerns merit further study, especially on the behaviour of GIOs in the open environment. The framework for strategic planning in the deployment of GIOs should be formulated with sustainability as the primary concern.
3. Risks and Benefits Related to GM Crops:
Public concerns about the use of LMOs lie in four major areas – food safety, the environment, socio-economic and ethical issues. First, in relation to food safety, there are concerns about assessing the risks of genetically modified (GM) foods to human health and understanding potential benefits of new GM foods to consumers. Secondly, in relation to environmental effects, the concerns relate to assessing the risks and benefits of releasing LMOs into the environment and the effects such releases may have on the environment. These may be direct effects, such as on biodiversity, or indirect, through changing agricultural practices that affect the environment. LMOs released for agricultural purposes may be plants, trees, livestock, fish and/or microorganisms.
Given the rapid pace of new developments in agricultural biotechnology, many consumers are seeking further information about the potential effects of biotechnology on their food and their environment. The media have sensed that this is an issue high in public consciousness and are actively promoting widespread debate on how we should best use the discoveries of modern genetics. This is one of the most important public debates of the new millennium, because its resolution will have global implications for food and raw material production for the rest of this century.
Risk Factors:
There are several areas of public concern with regard to potential human health risks of GM foods. These relate to understanding the potential of proteins and/or other molecules in GM foods to cause allergic reactions, to act as toxins or carcinogens and/or to cause food-intolerance reactions among the population. Methods of testing and evaluating these types of risks have been established for food and these are being applied to GM foods so as to detect any increased risks associated with particular foods.
A recent consultation between the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) reported that ‘the Consultation was satisfied with the approach used to assess the safety of the genetically modified foods that have been approved for commercial use’.
The US Food and Drug Administration (FDA) has also stated that ‘we have seen no evidence that the bioengineered foods now on the market pose any human health concerns or that they are in any way less safe than crops produced through traditional breeding’.
Although no instances of harmful effects on human health have been documented from GM foods, it does not mean that risks do not exist as new foods are developed with novel characteristics. GM foods should be assessed on a case-by-case basis, using scientifically robust techniques, so as to ensure that the foods brought to market are safe for human consumption.
For example, any protein added to a food should be assessed for its potential allergenicity, whether it is added by genetic engineering or by manufacturing processes. Allergenicity can be raised in foods either by raising the level of a naturally occurring allergen (e.g. in groundnuts) or by introducing a new allergen. More than 90% of the food allergens that occur in 2% of adults and 4-6% of children are associated with eight food groups. These include Crustacea, eggs, fish, groundnuts, soybean, tree nuts and wheat.
These foods merit close attention when examining GM foods for the potential for increased risk of allergenicity. There is also a need to assess the allergenic potential of unknown proteins, such as those produced by Bt genes in plants. It was the presence of a heat-tolerant Bt protein in Star-link maize that caused the US FDA to withhold approval for its use in human consumption, as the FDA scientific advisory panel considered that this protein posed a moderate allergy risk.
Antibiotic Resistance:
There are also concerns about the risk that the antibiotic-resistance genes used as selectable markers in GM plants may transfer to microorganisms that are human pathogens, adding to the increasing problem of antibiotic resistance in human pathogens. This problem is the result of widespread use of antibiotics in human and animal health.
WHO, the Organization for Economic Cooperation and Development (OECD) and FAO have assessed the antibiotic-resistance markers used in transgenic crops as being safe. The risk of transfer of an antibiotic marker from a GM food to a human pathogen is considered remote. Nevertheless, the use of these antibiotic markers is being phased out. Other selectable markers that can be removed from the plant in the development phase are replacing them.
Risk Assessment:
The International Life Sciences Institute (ILSI) has developed a decision tree that provides a framework for risk assessment in foods. It uses the following criteria, that an introduced protein in a food is not a concern if – (i) there is no history of common allergenicity; (ii) there is no amino acid sequence similar to those of known allergens; (iii) there is rapid digestion of the protein; and (iv) the protein is expressed at low levels.
For example, these risk assessment techniques were used to test the safety of increasing the protein content in soybean by introducing a protein from Brazil nut. However, food allergy tests showed that this transferred a potential allergen to soybean. Hence, further development of this GM high-protein soybean ceased.
The techniques for assessing the potential for allergenicity, toxicity and carcinogens in food are well established and should be readily able to be used by trained professionals in many countries. Given increasing global concerns about food safety, all countries will need to have in place food-safety regulations and the human and institutional capacity to be able to ensure the safety of their food supply.
Benefits of GM Crops to Human Health:
The risks in GM foods need to be weighed against the benefits. The next generation of GM foods is likely to include a number of functional foods that offer some nutritional benefits to consumers.
Human health benefits of GM foods lie in the potential for introducing traits that enable factors such as the following:
a. Improved nutritional quality of foods (e.g. higher vitamin content, lower fat content).
b. Reduced toxic compounds in food (e.g. cassava with lower levels of cyanide).
c. Crops grown with lower levels of chemical pesticides, thus reducing pesticide residues in food.
Labelling:
A key concern of consumers is being able to identify those foods that may contain allergens and other potentially harmful substances. Those who have allergic or food-intolerant reactions to particular foods can avoid them.
Others may wish to avoid certain foods on health, ethical or religious grounds. Informative food labelling, whether mandatory or voluntary, could be used to provide information about specific products and enable consumers to make informed decisions about their use, in terms of both risks and potential beneficial effects.
4. Future Research and Development of GM Crops:
There are some promising new developments in R & D that may assist in the design of future GM crops that would have clear benefits to the environment and that would mitigate some of the environmentally damaging effects of agricultural intensification.
a. Securing fungal resistance in adult plants by ‘switching on’ resistance genes that are active in the seed, but not currently in adult plants. This seems to be an elegant and safe use of biotechnology that could lead to significant reductions in fungicide use.
b. Achieving insect resistance by altering physical characteristics of plants, perhaps by increasing hairiness or thickening the plant cuticle. This could reduce insecticide use, without using in-plant toxins.
c. Altering the growing characteristics of crops (for example, shortening the growing season or changing the timing of harvests) offers the prospect of allowing more fallow land and less autumn planting. The recent discovery of dwarfing genes could be a significant step towards the production of higher-yielding and more reliable spring-sown cereals.
d. Developing crops (including trees) that can tolerate high levels of natural herbivory and yet remain viable.
e. Preventing out-crossing by engineering pollen incompatibility and other mechanisms into crops. This could significantly reduce the risk of spread of GM traits into native species.
Many of these traits could simply be transferred from one crop variety into another or be accomplished by switching on or off genes already present in the plant. Such transformations are likely to be more acceptable to the public than moving genes between phyla. The consequences of short-circuiting genetic distance between species, which has been maintained over long periods of time and geographical isolation, are not yet well enough understood to be able to assess the risks.
Biotechnology and the new science of genomics, which is giving new insights into how genes function, offer a whole new range of options for how to use land. For the first time, it may be possible to design crops to suit the land and the purpose rather than having to adapt land and purpose to suit the crop. These could become important components of sustainable farming systems that combine yield increases with environmental sustainability.
This is also important for developing countries where biotechnology may be able to offer new solutions to old problems of crop pests and disease in locally adapted crops, rather than trying to export conventional, chemically based agriculture with its damaging effects on biodiversity and the wider environment.
Ecological Research:
There are concerns that the science needed to be able to assess these ecological risks is not being undertaken. At the moment we do not know what effect escaped genes might have on natural and farmland ecosystems. This lack of science is disturbing, given the commercial pressure for the introduction of GM crops into the landscape.
There is clearly a need to set up effective monitoring systems to detect gene transfer and research to assess its ecological impacts. Research in this area would be in the interests of both the industry and the environment as it would yield data that would form a scientific basis for regulatory decisions.
There may also be scientific options that could be used in future generations of GM crops that would mitigate some of the ecological risks. For example, it may be possible to include in GM crop plants inbuilt mechanisms, such as pollen incompatibility, to prevent gene flow. Another means to ensure genetic isolation is to make sure that, wherever possible, plants used for transformations are unrelated to native species and edible crops within the intended market territory.
This principle would influence the choice of which plants companies choose as platforms for biomedical and industrial product transformations (e.g. higher starch production, vaccine production in plants). If gene technology is to become a standard technique for plant breeding, genetic isolation of crops from the rest of the living environment may become normal practice, as will the removal of marker genes for antibiotic resistance.
5. International Developments for Safety of GM Crops:
As a result of an international conference on the safety of GM crops, the OECD noted the needs for the following:
a. Factual points of departure as to where there is agreement and disagreement on human health risks.
b. Benefits versus risks, which differ for different countries and environments.
c. Management of genetic modification technologies.
d. The role of stakeholders and consultative processes.
e. An international programme of activities to inform the public debate and policy-making, including a possible international panel to review scientific evidence on the benefits and risks of the applications of new biotechnologies in food.
The International Council of Scientific Unions (ICSU) has initiated a review of the scientific basis of assessing risks and benefits of GM foods, as a contribution to the ongoing debates, nationally and internationally.