Genetically Modified Crops: A Technology for the 21st Century
Presented at the South African Poultry Association and the South African National Seed Organisation Annual Meetings, in Johannesburg South Africa May 2002.
by Richard H Phipps
Principal Research Fellow at the Centre for Dairy Research, Department of Agriculture, The University of Reading, Reading RG6 6AT United Kingdom
1. Historical Perspective and Global Reality Check.
In the 1960′s the Green Revolution heralded one of the major agricultural developments of the last century. The production of new cereal varieties, coupled with increased use of fertilisers, irrigation and pesticides, provided many of the technological inputs required to feed an expanding world population. Whilst synthetic pesticides have been used extensively to reduce crop losses 41% of total annual production of eight major world crops is destroyed by insects, diseases and weeds.
Currently world population is increasing rapidly, particularly in developing countries and world food production, which doubled in the last 35 years, will have to double again in the next 15 years. Against this background the area and quality of land available for crop and livestock production is decreasing and the rate of crop improvement through conventional breeding is slowing down. Under these conditions the ability to decrease the environmental impact of agriculture while maintaining or improving its productivity and sustainability will be a major problem and will have no single easy solution and can not be achieved by “more of the same” Tillman (1999).
In addressing the requirements to meet the increasing global demand for crop and animal products we must consider technologies which will reduce energy inputs (fertiliser, pesticide and farm operations), increase crop yields, improve feed quality, reduce crop losses in a manner that provides improved safety for the environment and people. While it is recognised that there are many controversial issues associated with the introduction of GM technology, the paper reviews some of the potential benefits and addresses some of the concerns associated with this new technology.
2. Technology Update
The Global Review of Commercialised Transgenic Crops produced by Clive James (2000) states that between 1996 and
2001 the area of GM crops grown globally increased from 2 to 53 million ha at adoption rates which are unprecedented and the highest for any new technology that has ever been presented to agriculture. While the area grown in 2000 has increased, the rate of increase has slowed due to the controversial nature of the technology. Although over 50 different crops have been genetically modified for a range of different input traits the main GM crops currently grown commercially are soyabean (33 million ha), maize (8 million ha), cotton (2 million ha) and canola (3 milliom ha) and the main input traits are herbicide tolerance and insect protection. Although North America and Argentina were responsible for the vast majority of the area grown, China,
Australia, South Africa, Mexico, Spain, France, Portugal, Rumania and the Ukraine have all grown transgenic crops and India has recently approved commercial planting of insect protected cotton. These crops, which have been modified for agronomic traits are generally, referred to as First Generation GM crops. The Second Generation of GM crops, which have enhanced nutritional characteristics, are currently in field trials, but are not yet in commercial production.
3. Issues of safety
- 3.1 Substantial equivalence
In 1993 OECD formulated the concept of Substantial Equivalence as a starting point for the safety assessment of GM crops. The concept has since been developed further (OECD,
1996 and 1998) and has obtained broad international consensus and is applicable to both foods and feeds (Kuiper, et al 2001, Chesson 2000).The concept is based on the idea that existing crops can serve as the basis for comparing the properties of a GM crop with an appropriate counterpart considered safe as shown by a long history of safe use. Application of the concept is not a safety assessment per se but helps to identify similarities and differences between conventional and GM crops. Differences are then the subject of further investigation.Agronomic, phenotypic and compositional analysis of key nutritional components are the basis for establishing substantial equivalence. Padgette et al. (1996), Taylor et al. (1999) and Stein (2000) all provide excellent examples of the compositional analyses conducted during this process. From the numerous reports in the published literature Table 1 illustrates some of the data which demonstrates that conventional and Roundup Ready soybean have similar composition as measured by laboratory analyses (Linderman et al. 2001).Table 1: Compositional equivalence
Soybean Meal Composition (% DM) Conventional
Roundup Ready GM DM 90.3 91.0 Crude Protein 51.5 51.2 Neutral Detergent
4.95 4.85 Lysine 3.16 3.09 Meth + Cystine 1.47 1.51
Numerous feeding studies with both monogastric and ruminant livestock have now been completed to compare diet digestibility, feed intake, milk production milk composition, feed efficiency and live-weight gain of animals fed either GM or conventional feed ingredients. These studies clearly established that GM feed ingredients were nutritionally equivalent to their isogenic non-GM counterpart and to commercially available varieties and have been reviewed by Clark and Ipharraguere, 2000 and Artim et al.
2002). Table 2 illustrate one such study (Piva et al 2002) but draws attention to the fact that the performance of the pigs was significantly higher when offered the GM based diet and this was attributed to the fact that GM insect protected maize grain had a significantly lower mycotoxin content when compared with the conventional maize grain. Piva et al. (2001) have also noted similar production benefits with poultry.
Table 2: Nutritional Equivalence comparing conventional and Bt maize grain.
|Pigs: at 2 locations||Conventionalmaize||Bt maize grain||Significance|
|Daily gain||375||396||P < 0.05|
|Final Live-weight||22.0||22.6||P < 0.05|
- 3.2 Potential allergenicity
One of the primary concerns over the safety of GMOs is the possibility that the novel protein expressed by the introduced gene may cause an allergic reaction. A decision-tree approach has been widely adopted as an allergy assessment strategy (Joint FAO/WHO Expert Consultation 2000). The strategy focuses on the source of the gene, level and site of protein expression, sequence homology of the newly introduced protein to known allergens and the physicochemical properties of the newly introduced proteins.Far from increasing the risk of allergenicity the Joint FAO/WHO report stated that genetic modification offers the opportunity to reduce or eliminate protein allergens that occur naturally in specific foods such as wheat and peanuts and recommended that further work in this area should be encouraged (Nakamura and Matsuda, 1996; Astwood and Fuchs, 1996).To-date, with over 60% of products on supermarket shelves in the USA containing GM ingredients and after their consumption by over 300 million Americans for 7 years there has not been one single authenticated case of a health problem attributed to the consumption of GM food. While this is not proof positive in the classical experimental manner, we should be aware that this has taken place in the most litigious society in the world.
- 3.3 Consumption of Transgenic DNA and Gene Products derived from GMOs.
Concern was expressed that transgenic DNA and gene products may be transferred to and accumulate in milk, meat, eggs derived from animals fed GM crops and whether the consumption of these animal products would lead to adverse health effects in humans? Beever and Kemp (1999) have reviewed the fate of DNA and protein in the digestive tract of monogastric and ruminant livestock and have emphasized the extensive and aggressive nature of the digestive tract of livestock.With respect to the consumption of DNA, the World Health Organisation has concluded that there is no inherent risk in consuming DNA, including DNA from genetically modified crops. The basis of their conclusion was that mammals have alwaysconsumed significant quantities of DNA from a wide variety of sources, including plants, animals, bacteria, parasites and viruses. Consumption of DNA is not considered as a safety issue by regulatory agencies in US, Canada, Japan or the EU.Nevertheless a number of studies have been conducted to determine if transgenic DNA and gene products can be found in milk meat and eggs. Using extremely sophisticated Polymerase Chain Reaction analyses transgenic DNA and gene products have not been identified in food derived from animals fed GM feed ingredients (Ash et al. 2000, Phipps et al. 2002).
Perhaps we should asked, why if we go to these lengths for crops produced by GM technology where one or two extremely well characterised genes are introduced, no such procedures are contemplated for new varieties developed from conventional breeding techniques which may involve radiation and chemical mutanogenesis with no knowledge as to the possible effects of the new genes.
4. Some of the Potential Benefits of first generation GM Crops
The rapid uptake by farmers indicates grower satisfaction with GM crops. Flexible crop management systems, improved productivity, increased financial returns, a safer working environment, and reduced environmental impact of farming systems have all been given as reasons for switching to GM crops. Consumers have been led to believe that first generation GM crops primarily benefit farmer and offering them little or no benefit. This is incorrect and some consumer benefits are illustrated below.
- 4.1 Reduced pesticide use, increased use of conservation tillage and safer food While a number of environmental concerns have been raised about the introduction of GM crops it is only recently that their effects on pesticide use has been documented. Phipps and Park (2002) have recently reviewed this topic and have estimated that in the year 2000 the introduction of GM crops reduced pesticide use by 23 million kg of formulated product. India has recently approved the commercial planting of Bt cotton and Phipps and Park (2002) estimated that if 50% of the Indian cotton crop was grown as GM varieties, this would result in a reduction in pesticide use of 9 million kg/year. They also drew attention to reports which showed that GM crops could reduce the number of field operations (tractor use), which resulted in a significant reduction in diesel use with a subsequent reduction in emissions of the greenhouse gas carbon dioxide.Estimates also indicated that if GM crops were widely grown in the EU pesticide use in the EU/annum would decrease by 14 million kg of formulated product. In addition there would be a reduction of 8 million ha sprayed which would save 21 million litres of diesel and result in a reduction of approximately 73,000 tonnes of carbon dioxide being released into the atmosphere. They also emphasised that these changes, particularly in developing countries resulted in greatly improved health of farmers who were responsible for spraying these crops (Tables
3).Table 3: Reduced pesticide use and improved health from the introduction of Bt cotton
Cotton Conventional varieties Bt Cotton Spray rate (kg/ha) 52 16 Number of sprays/ha 20 7 Illness (%) 30 9
GM technology has resulted in a huge increase in the use of conservation/minimum tillage. This has resulted in reduced soil erosion, reduced run off of fertilisers and pesticides, greatly improved water quality and increased biodiversity in arable land.
- 4.2 Improved food and feed quality.While the use of insect protected (Bt) crops will increase yields by reducing insect damage it also reduces mycotoxin contamination arising from fungal attack on damaged grain (Munkvold et al., 1998). The result is not only more grain but safer grain for both humans and livestock.
5. Some benefits of second generation of nutritionally enhanced GM crops
Many millions of the poorest people in the world live in marginal areas subjected to low and erratic rainfall, extremes of soils conditions, and extremes of temperatures. Work is in progress to modify plants to withstand these abiotic stresses.
Maize and rice are the staple diets for a large proportion of the world population. Yet these crops are nutritionally poorly balanced being low in protein and deficient in some key nutrients such as essential amino acid and micro-nutrients such as vitamins. Work on improving these traits through genetic modification is well advanced. For example rice has been modified to contain increased levels of Provitamin A, which will help reduce the number of children (500,000/year) whose eye sight is seriously impaired by vitamin A deficiency. Crops have also been modified to contain higher levels of available iron to help reduce the chronic anaemia, which effects millions of women mainly in the developing world.
Soybean and canola have been modified for a range of nutritional characteristics which include improved fatty acid content which can reduce the saturated fat levels in milk and meat making both products more nutritious.
Apples are being modified to prevent dental decay by controlling the growth of Streptococcus mutans the bacteria that causes tooth decay. Coffee plants have been modified to restrict the synthesis of caffeine, with the result that there is no need for the solvent extraction process currently used to remove caffeine andproduce decaffeinated coffee.
In addition crops are being modified to act as edible vaccines, which can reach more people and offer a more sustainable method of health protection than the current programmes are in development (Brand 1999).
Maize and soybeans, which are integral components of both monogastric and ruminant livestock feeding systems, have been genetically modified for enhanced nutritional characteristics. These modifications include improved nutrient availability, enhanced amino acid and fatty acid composition and reduced anti-nutritional factors. For example maize has been modified to have a low phytate content which will allow better phosphate bioavailability; thus reducing phosphates entering waterways.
Current agricultural production systems cannot continue in their present form and there is a need for new technology that can produce more food of improved nutritional value and can reduce crop losses in an environmentally acceptable and sustainable manner. The current paper presents information, which shows that GM technology, which is governed by robust regulatory agencies, can contribute significantly to these aims. As with all new technology the introduction of GM crops has been controversial. However the current paper outlines some of the many advantages of both first and second generation crops and emphasises that GM crops and food and feed derived from them are at least as safe, if not safer than, than form conventional plants.
Some Key References
Ash J.A., Scheideler S.E., Novak C.L., 2000. The fate of genetically modified protein from Roundup Ready soybeans in the laying hen. Poultry Science Association Annual Abstracts Supplement 1 pp. 26.
Astwood J., Fuchs R.L., 1996. Preventing Food Allergy: Emerging Technologies. Trends in Food Science & Technology,
1996, 7, 219-226.
Beever D.E., Kemp C.F., 2000. Safety issues associated with the DNA in animal feed derived from genetically modified crops. A review of scientific and regulatory procedures. Nutrition Abstracts
Clark J.H., Ipharraguerre I.R., 2000. Livestock performance: feeding biotech crops. Agricultural Biotechnology in the Global Marketplace. J. Dairy Sci. 84(E Suppl.):E9-E18. American Dairy Science Association. Savoy, IL.
FAO/WHO, 2000. Safety aspects of genetically modified foods of plant origin. Report of a Joint FAO/WHO Expert Consultation on Food Derived from Biotechnology. World Health Organisation Headquarters Geneva Switzerland.
James C., 2001. Preview of the global review of commercialised
transgenic crops 1999. ISAAA Briefs No.12. The international Service for the Acquisition of Agri-biotech Applications (ISAAA), Ithaca, New York.
Metcalfe D.D., Astwood J.D., Townsend R., Sampson H.A., Taylor S.L., Fuchs R.L., 1996. Assessment of the allergenic potential of foods derived from genetically engineered crop plants. Critical reviews in Food Science and Nutrition 36 S165- S186.
Munkvold G.P., Hellmilch R.L., Rice L.G., 1998. Comparison of Fumonisin Concentrations in Kernels of Tansgenic Bt Maize Hybrids and Non transgenic Hybrids,” Plant Disease, 83, 130-
Padgette S.R., Taylor N.B., Nida D.I., Bailey M.R., MacDonald J., Holden M.R., Fuchs R.L., 1996. The composition of glyphosate- tolerant soybean seed is equivalent to that of conventional soybeans. J. Nutr. 126, 702-716.
Phipps, R.H. and Park, J.R. (2002). Environmental benefits of genetically modified crops: Global and European perspectives on their ability to reduce pesticide use. Journal of Animal and Feed Sciences 11, 1-18
Phipps R.H., Beever, D.E. and Tingey, A.P. 2001. Detection of transgenic DNA in bovine milk: results for cows receiving a TMR containing Bt insect protected maize grain (MON810). J. Anim. Sci. 79 (Suppl.1)/J. Dairy Sci. 84 (Suppl. 10), 114
Piva,G., Morlacchini, M., Pietri,, A. and Prandini, A., 2001. Growth and performance of broilers fed insect-protected (MON810) or near isogenic control corn Poultry Science 80 (Suppl. 1) Abstract 1324
Taylor N.B., Fuchs R.L. MacDonald J., Shariff A.R., Padgette, S.R., 1999. Compositional analysis of glyphosate-tolerant treated with glyphosate. J. Agric. Food Chem. 47, 4469-4473.