Genetic Engineering In Agriculture Essay
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Introduction
Among the millions of species that inhabit the planet, only twenty species provide ninety percent of the human food supply (Montgomery 2000). Since the introduction of genetic engineering, however, livestock and crops have a more productive future. Transfer of engineered genes from organism to organism occurs through hybridization, conjugation, and transformation in microorganisms. By the substitution of genes into agricultural species, biodiversity can flourish to improve social and economic development. Although methods of gene and DNA implantation quickly develop advanced products, even precise genetic alterations do not ensure that the environment will remain balanced or that changes in the genome will not occur. With careful design and a good understanding of transgenic organisms, minimal ecological and social risks will occur with the development of genetically engineered organisms.
Background
To improve methods of plant breeding, farmers turn to the hybridization of genes. New genes from wild species are transferred into cultivated varieties of similar crops to attain desired traits. Specific properties such as disease resistance, stress tolerance, and nutritional qualities are advantageous to the farmer because more time is spent on cultivation rather than outside interferences. However, crossbreeding results in mass amounts of genes transferring to the plant recipient, only a few of which are desired. Thus, only sexually compatible species of the crop can be used to breed (Horsch 1993). Farmers using crossbreeding and hybridizing methods are able to attain improved products, but could cause great damage to the genome in the transfer of unknown, undesired genes (Geweke 1999).
In more recent biotechnology, breeders are turning to genetic transformation as a more precise method of genetic engineering. Instead of transferring large blocks of genes from donor plant to recipient, small isolated blocks of genes are put into the plant chromosome through biolistics, vectors, or protoplast transformation (Horsch 1993). Biolistics is a technique that shoots the gene block into the potential host cell. In order for the process to succeed, the microscopic particles and DNA must enter the cell nuclei and combine with the plant chromosome. Biolistics is commonly used but has a slight failure risk since the breeder has little control over the destination of the gene block (Mooney & Bernardi 1990). Bacteria or viruses can also carry the gene blocks into a new cell. Common vectors in gene transfer between plants are Agrobacterium tumefaciens and Agrobacterium rhizogenes. In the soil, the bacteria will infect the plants with their own plasmid, transferring the desired gene that was placed in the bacteria’s DNA. Vector gene transfer is a preferred method of transformation since this modification already occurs naturally in the environment (Rudolph & McIntire 1996). Last is protoplast transformation, which uses enzymes to dissolve the cellulose in the plant wall that leaves a protoplast. Once a specific gene block is added to the protoplast, the cell wall will re-grow into a transgenic plant.
Direct manipulation of DNA focuses on selective breeding, altering organisms to achieve higher quality products and more of them. These improved crop modifications center either on agronomic traits or quality traits (Nielsen 1999). Reductions of herbicides, insecticides, and water usage are some effects of replacing plants with desired properties. Farmers choose these agronomic traits to reduce their costs of poisons and water, therefore increasing profitability. Quality traits focus more on the consumer of the product. By improving product characteristics such as phenotype, nutritional value, and preservation, consumers will benefit. In return, agricultural industries will be able to sell products at a higher price and increase their profit in the near future.
Beneficial crop modification through agronomical trait selection
Transgenic organisms can be designed to minimize the chance of environmental risks. The agronomic traits that farmers select for crops improve the control of pest insects, plant pathogens, weeds, and water. The main toxin used for insect pest control is a gene from the bacterium Bacillus thuringiensis (Bt). By inserting the Bt virus, crops have an internal resistance to insects and pests, which allows the farmer to decrease insecticide sprays. Agrochemicals serve as a good protection against insects, but are not as ecologically sound as gene transformation since outside plants and trees can be accidentally sprayed (Horsch 1993). Although seed price will increase, the total cost of seeds and agrochemicals will decrease, helping the farmer gain profit. Today, several crop plants and trees have been inserted with the bacterium strain and show effective resistance against pests such as caterpillars and beetles. In addition, engineered Bt has been approved for use as a conventional insecticide (Nottingham 1996).
Plant pathogen control can also help reduce costs for the farmer. In 1998, K1026 from Agrobacterium radioloacter was introduced as a genetically engineered bacterial strain to help control crown gall disease in pitted fruit trees (Paoletti & Pimentel 1996). The disease control proved highly effective, leaving farmers with a more abundant crop of fruit and a higher financial intake. Modifications of fungi are also beginning to arise as an excellent plant pathogen control. Metarhyzium anisopliae is used to protect plants against the benomyl fungicide. Pathogenic fungi are another promising goal because high yields of fungicides will not reduce the effectiveness of the entomophagus fungus. Today, 75% to 100% of agricultural crops contain some degree of host plant resistance (Paoletti & Pimentel 1996).
The herbicide resistance gene is derived from glyphosate, an herbicide that produces a surplus of target enzymes (EPSPS). In transgenic petunias that contained the EPSPS enzyme, glyphosate could be used heavily since the plant was tolerant to normally lethal concentrations (Horsch 1993). After much research, EPSPS genes that have a greater tolerance to glyphosate were found, cloned, and expressed in many transgenic plant crops. Farmers with herbicide-resistant crops will not have problems with weed control. The amount of failed crop seasons will also be reduced and the market price will decrease since more products are grown. However, more money will by spent on herbicides since the EPSPS gene allows heavier usage of them. In the end, farmers with herbicide-resistant crops should gain more profit from the increased crop production, which brings in more money than what is spent on herbicides.
The last consideration of agronomical trait selection is soil and water usage. In order to control weeds, crop soils need to be tilled to up-root weeds. However, with the mass reduction in weeds due to herbicide-resistant crops, the soil can remain un-tilled and decrease the amount of machine work done by the farmer. With little use of farming machines, pollution is decreased and crops are not infected with exhaust from the gasoline (Altiere 1998). Crops can also be engineered to tolerate drought. During dry seasons, farmers with drought-resistant crops do not have to use much irrigation water, saving another expenditure for the farmer.
Beneficial crop modification through quality trait selection
Aside from the farmer, consumers and food companies also benefit from transgenic genes. Modifying organisms with quality traits positively affects consumer health, the actual product, the environment, and food business. Genetically modified food can help develop new sources of human therapeutics and provide more nutritional value than normal food crops. According to the Ministry of Agriculture and Forestry in New Zealand, US researchers developed a banana with an antigen from the hepatitis B virus in 1996. If research continues, a vaccine could be produced that would cost only a fraction of the current hepatitis B vaccine. Other raw fruits contain helpful antigens that could be engineered to prevent disease at low costs. Nutritional value of food, such as vitamin, mineral, carbohydrate, protein, and fat content, can also be increased or decreased with genetic engineering (Pollan 1998).
Better products create better consumer sales and higher industry profit. Quality traits that alter the phenotype of a crop are produced to attract consumers to the food. For example, red delicious apples can be transformed to be brighter red and not oxidize as quickly when being preserved. Onions could also be genetically engineered to reduce the amount of fumes released when cutting them, preventing consumers from tearing (Nottingham 1996). If more consumers buy products due to improved characteristics and higher attraction, food industries can make more sales. Food companies with increased profits are then able to continue the production and sale of genetically modified food.
When consumers buy food products, many people want them to be naturally produced or environmentally safe. With herbicide- and insect-resistant crops, fewer chemicals are used on the plants and help reduce the amount of pollution in the atmosphere. Although the crops are not “naturally” produced, man-made substances are used less and the genes transferred to the modified plants are from other wild vegetation (Nielsen 1999).
The benefits that arise from introducing quality traits into crops happen because of the profits gained in the food industry. Although genetically modified food is more expensive, consumers are more willing to pay for vaccine research in bananas and chemical free products. According to the Ministry of Agriculture and Forestry in New Zealand, global market values for genetically modified crops is expected to be up to six billion dollars in the year 2005. Using genetic technology, the development process of organisms is quicker, reducing breeding cycles of fifteen years to only two or three years (Paoletti & Pimentel 1996). With more crops being produced rapidly, businesses are able to run a company of increasing profitability and decreasing management costs (Nielsen 1999).
Risks associated with transgenic organisms
Genetic engineering in agriculture provides many benefits to social, economic, and environmental welfare. However, ecological risks are unavoidable, even under careful monitoring (Altieri 1998). According to Rissler and Mellon (1996) the most serious risks of transgenic crop use include: simplifying crop systems and promoting genetic erosion, the potential transfer of genes from pesticide-resistant crops to wild vegetation, the generation of new virulent strains of viruses, insect resistance to Bt toxin, and the destruction of natural relationships in the ecosystem. Although all of these cases have not yet been proven, signs of ecological imbalance and environmental hazards have already appeared through the application of genetic engineering (Regal 1996).
Total weed removal by herbicides may lead to undesirable ecological impacts (Altieri 1998). Weed diversity in and around crop fields is important to the balance of the ecosystem because weeds provide insect pest control, reduce erosion by covering soil, and help prevent insecticides from spraying into forests. The complexity of the agro-ecosystem will also be reduced. Low plant diversity caused by the elimination of weeds will enhance free-range weed growth, insects, and disease since other organisms will not fill the empty ecological niches (Rissler & Mellon 1996). As herbicides continue to become more and more effective, species that have adapted to the herbicides will become the favoring competitor, further reducing plant diversity and replacing the natural species with transgenic organisms.
Another major ecological risk comes from the release of transgenic crops into the wild. Gene-altered crops may transfer their cross genes to other plants, creating new weed species in the wild (Levin & Strauss 1991). Altieri (1998) refers to these new species as “super weeds.” The main concern of “super weed” growth is the hybridization between distinct plant species, which cannot be controlled in the wild. Many crops are grown near plants with some degree of cross compatibility, such as Raphanus raphanistrum and Sativus, a cross of wild radishes with genetically engineered radishes (Wright 1996). If release of transgenic crops continues, “super weeds” will eventually control the main population of wild and domestic plants, reducing biodiversity.
Disease-resistant crops could also impact the ecological system. New pathogens might occur by the recombination between RNA virus and a viral RNA inside the transgenic crop, leading to even more severe disease problems (Rissler & Mellon 1996). Researchers such as Geweke et al. (1999) have shown that under specific conditions of recombination, new viral strains with altered host range have occurred in transgenic plants. This possibility that virus-resistant plants may widen the host range of some viruses or produce new virus strains in transgenic plants requires thorough experimental investigation under strict regulatory control (Paoletti &...
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