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TRANSGENIC PLANTS AND WORLD AGRICULTURE EXAMPLES OF GM TECHNOLOGY THAT WOULD BENEFIT WORLD AGRICULTURE GM technology has been used to produce a variety of crop plants to date, primarily with “market-led” traits, some of which have become commercially successful. Developments resulting in commercially produced varieties in countries such as the United States and Canada have centered on increasing shelf life of fruits and vegetables, conferring resistance to insect pests or viruses, and producing tolerance to specific herbicides. While these traits have had benefits for farmers, it has been difficult for the consumers to see any benefit other than, in limited cases, a decreased price owing to reduced cost and increased ease of production (Nelson et al. 1999; Falck-Zepeda et al. 1999). A possible exception is the development of GM technology that delays ripening of fruit and vegetables, thus allowing an increased length of storage. Farmers would benefit from this development by increased flexibility in production and harvest. Consumers would benefit by the availability of fruits and vegetables such as transgenic tomatoes modified to soften much more slowly than traditional varieties, resulting in improved shelf-life and decreased cost of production, higher quality and lower cost. It is possible that farmers in developing countries could benefit considerably from crops with delayed ripening or softening, as this may allow them much greater flexibility in distribution than they have at present. In many cases small-scale farmers suffer heavy losses due to excessive or uncontrolled ripening or softening of fruit or vegetables.
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TRANSGENIC PLANTS AND WORLD AGRICULTURE The real potential of GM technology to help address some of the most serious concerns of world agriculture has only recently begun to be explored. The following examples show how GM technology can be applied to some of the specific problems of agriculture, indicating the potential for benefits. Pest Resistance There is clearly a benefit to farmers if transgenic plants are developed that are resistant to a specific pest. For example, papaya-ringspot-virus-resistant papaya has been commercialized and grown in Hawaii since 1996 (Gonsalves 1998). There may also be a benefit to the environment if the use of pesticides is reduced. Transgenic crops containing insect-resistance genes from Bacillus thuringiensis have made it possible to reduce significantly the amount of insecticide applied on cotton in the United States. One analysis, for example, showed a reduction of 5 million acre-treatments (2 million hectare-treatments) or about 1 million kilograms of chemical insecticides in 1999 compared with 1998 (U.S. National Research Council 2000). However, populations of pests and disease-causing organisms adapt readily and become resistant to pesticides, and there is no reason to suppose that this will not occur equally rapidly with transgenic plants. In addition, pest biotypes are different in various regions. For instance, insect resistant crops developed for use in the United States and Canada may be resistant to pests that are of no concern in developing countries, and this is true both for transgenic plants and those developed by conventional breeding techniques. Even where the same genes for insect or herbicide resistance are useful in different regions, typically these genes will need to be introduced into locally adapted cultivars. There is need, therefore, for more research on transgenic plants that have been made resistant to local pests to assess their sustainability in the face of increased selection pressures for ever more virulent pests.
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TRANSGENIC PLANTS AND WORLD AGRICULTURE Improved Yield One of the major technologies that led to the “Green Revolution” was the development of high-yielding semi-dwarf wheat varieties. The genes responsible for height reduction were the Japanese NORIN 10 genes introduced into Western wheats in the 1950s (Gibberellin-insensitive-dwarfing genes). These genes had two benefits: they produced a shorter, stronger plant that could respond to more fertilizer without collapsing, and they increased yield directly by reducing cell elongation in the vegetative plant parts, thereby allowing the plant to invest more in the reproductive plant parts that are eaten. These genes have recently been isolated and demonstrated to act in exactly the same way when used to transform other crop plant species (Peng et al. 1999). This dwarfing technique can now potentially be used to increase productivity in any crop plant where the economic yield is in the reproductive rather than the vegetative parts. Tolerance to Biotic and Abiotic Stresses The development of crops that have an inbuilt resistance to biotic and abiotic stress would help to stabilize annual production. For example, rice yellow mottle virus (RYMV) devastates rice in Africa by destroying the majority of the crop directly, with a secondary effect on any surviving plants that makes them more susceptible to fungal infections. As a result this virus has seriously threatened rice production in Africa. Conventional approaches to the control of RYMV using traditional breeding methods have failed to introduce resistance from wild species to cultivated rice. Researchers have used a novel technique that mimics “genetic immunization” by creating transgenic rice plants that are resistant to RYMV (Pinto et al. 1999). Resistant transgenic varieties are currently about to enter field trials to test the effectiveness of their resistance to RYMV. This could provide a solution to the threat of total crop failure in the Sub-Saharan African rice growing regions.
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TRANSGENIC PLANTS AND WORLD AGRICULTURE Numerous other examples could be given to illustrate the range of current scientific research, including transgenic plants modified to combat papaya ringspot virus (Souza 1999), blight resistant potatoes (Torres et al. 1999), and rice bacterial leaf blight (Zhai et al. 2000); or as an example of an abiotic stress, plants modified to overproduce citric acid in roots and provide better tolerance to aluminum in acid soils (de la Fuente et al. 1997). These examples have clear commercial potential but it will be imperative to maintain publicly funded research in GM technology if their full benefits are to be realized. For example, while GM technology provides access to new gene pools for sources of resistance, it needs to be established that these sources of resistance will be more stable than the traditional intra-species sources. Use of Marginalized Land A vast land-mass across the globe, both coastal as well as terrestrial, has been marginalized because of excessive salinity and alkalinity. A salt tolerance gene from mangroves (Avicennia marina) has been identified, cloned and transferred to other plants. The transgenic plants were found to be tolerant to higher concentrations of salt. The gutD gene from Escherichia coli has also been used to generate salt-tolerant transgenic maize plants (Liu et al. 1999). Such genes are a potential source for developing cropping systems for marginalized lands (M.S. Swaminathan, personal communication 2000). Nutritional Benefits Vitamin A deficiency causes half a million children to become partially or totally blind each year (Conway and Toennissen 1999). Traditional breeding methods have been unsuccessful in producing crops containing a high vitamin A concentration and most national authorities rely on expensive and complicated supplementation programs to address the problem. Researchers have intro-
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TRANSGENIC PLANTS AND WORLD AGRICULTURE duced three new genes into rice—two from daffodils and one from a micro-organism. The transgenic rice exhibits an increased production of beta carotene as a precursor to vitamin A and the seed is yellow in color (Ye et al. 2000). Such yellow, or golden, rice may be a useful tool to help treat the problem of vitamin A deficiency in young children living in the tropics. Iron fortification is required because cereal grains are deficient in essential micro-nutrients such as iron. Iron deficiency causes anemia in pregnant women and young children. About 400 million women of child-bearing age suffer as a result, and they are more prone to stillborn or underweight children and to mortality at childbirth. Anemia has been identified as a contributing factor in over 20% of maternal deaths (after giving birth) in Asia and Africa (Conway 1999). Transgenic rice with elevated levels of iron has been produced using genes involved in the production of an iron-binding protein and in the production of an enzyme that facilitates iron availability in the human diet (Goto et al. 1999; Lucca 1999). These plants contain 2-4 times the levels of iron normally found in non-transgenic rice, but the bioavailability of this iron will need to be ascertained by further study. Reduced Environmental Impact Water availability and efficient usage have become global issues. Soils subjected to extensive tillage (ploughing) for controlling weeds and preparing seed beds are prone to erosion, and there is a serious loss of water content. Low tillage systems have been used for many years in traditional communities. There is a need to develop crops that thrive under such conditions, including the introduction of resistance to root diseases currently controlled by tillage and to herbicides that can be used as a substitute for tillage (Cook 2000). Applications in more developed countries show that GM technology offers a useful tool for the introduction of root disease resistance for conditions of reduced tillage. However, a
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TRANSGENIC PLANTS AND WORLD AGRICULTURE careful cost-benefit analysis would be needed to ensure that maximum advantage is achieved. Regional differences in agricultural systems and the potential impact of substituting a traditional crop with a new transgenic one would also need to be carefully evaluated. Other Benefits of Transgenic Plants First generation transgenic varieties have benefited many farmers in the form of reduced production costs, higher yields, or both. In many cases, they have also benefited the environment because of reduced pesticide usage or by providing the means to grow crops with less tillage. Insects are responsible for huge losses to crops in the field and to harvested products in transit or storage, but health concerns for consumers and for environmental impact have limited the registration of many promising chemical pesticides. Genes for pest resistance, carefully deployed in crops to avoid selecting for future pest resistance, provide alternative opportunities to reduce the use of chemical pesticides in many important crops. In addition, lowering the contamination of our food supply by pathogens that cause food safety problems (e.g., mycotoxins) would be beneficial to farmers and consumers alike. Pharmaceuticals and Vaccines from Transgenic Plants Vaccines are available for many of the diseases that cause widespread death or human discomfort in developing countries, but they are often expensive both to produce and use. The majority must be stored under conditions of refrigeration and administered by trained specialists, all of which adds to the expense. Even the cost of needles to administer vaccines is prohibitive in some countries. As a result the vaccines often do not reach those in most need. Researchers are currently investigating the potential for GM technology to produce vaccines and pharmaceuticals in plants. This could allow easier access, cheaper production, and an alternative
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TRANSGENIC PLANTS AND WORLD AGRICULTURE way to generate income. Vaccines against infectious diseases of the gastro-intestinal tract have been produced in plants such as potato and bananas (Thanavala et al. 1995). Another appropriate target would be cereal grains. An anti-cancer antibody has recently been expressed in rice and wheat seeds that recognizes cells of lung, breast and colon cancer and hence could be useful in both diagnosis and therapy in the future (Stoger et al. 2000). Such technologies are at a very early stage in development and obvious concerns about human health and environmental safety during production must be investigated before such plants can be approved as specialty crops. Nevertheless, the development of transgenic plants to produce therapeutic agents has immense potential to help in solving problems of disease in developing countries. About one-third of medicines used today are derived from plants, one of the most famous examples being aspirin (the acetylated form of a natural plant product, salicylic acid). It is believed that less that 10% of medicinal plants have been identified and characterized, and the potential exists to use GM technology in a way that increases yields of these medicinal substances once identified. For example, the valuable anti-cancer agents vinblastine and vincristine are the only approved drugs for treatment of Hodgkin's lymphoma. Both products are derived from the Madagascar periwinkle, which produces them in minute concentrations along with 80-100 very similar chemicals. The therapeutic compounds are therefore extremely expensive to produce. Currently, there is intensive research in progress to investigate the potential of GM technology to increase the yields of active compounds, or to allow their production in other plants that are easier to manage than the periwinkle (Leech et al. 1998). We recommend that transgenic crop research and development should focus on plants that will (i) improve production stability; (ii) give nutritional benefits to the consumer; (iii) reduce the environmental impacts of intensive and
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TRANSGENIC PLANTS AND WORLD AGRICULTURE extensive agriculture; and (iv) increase the availability of pharmaceuticals and vaccines; while (v) developing protocols and regulations that ensure that transgenic crops designed for purposes other than food, such as pharmaceuticals, industrial chemicals, etc. do not spread or mix with either transgenic or non-transgenic food crops.
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