Environmental Safety of Genetically Engineered Crops

Current Status of Genetically Engineered Crops and Assessment of Environmental Impacts

31 Current Status of Genetically Engineered Crops and Assessment of Environmental Impacts Hector Quemada Genetically engineered (GE) crops have been commercially grown since 1996, when the first such crops were planted in the United States. Since then, the adoption of these crops has been rapid. James (2009) has provided an global overview of the current status of these crops: a total of roughly 134 million hectares (330 million acres) were grown worldwide in 2008; plantings of genetically engineered crops expanded from the the United States to 25 countries; North America was the largest producer of GE crops (the United States and Canada account for 64% of the world plantings) followed by South America with at least 34% of the hectarage (primarily in Argentina, Brazil, and Paraguay); globally, 77% of the soybean, 49% of the cotton, and 26% of the corn crop was planted to GE varieties in 2009; in Asia, the leading producers were India and China, with more limited production in the Philippines; while there was some production on all continents except Antarctica, the use has been more limited in Europe, Africa, and Australia. An estimated 14 million farmers planted GE crops in 2009, but because of differences in farm size, the great majority (90%) were in developing countries. The majority of the transgenic acreage planted worldwide is composed of only a few crops and traits. Soybean, maize, cotton, and canola account for the vast majority of area planted with transgenic varieties; insect resistance, herbicide tolerance, and the combination of the two are the most prevalent traits deployed (James 2009). In all commercial products to date, insect resistance has been achieved by introduction of various insecticidal proteins from the bacterium Bacillus thuringiensis (Bt). Most of the insecticidal proteins form crystals that accumulate in the bacterial spores. When consumed by an insect, the alkaline conditions in the insect gut release the toxin, which is highly specific to different orders of insects (e.g., Lepidoptera , Coleoptera, Diptera), depending on presence of the appropriate receptor molecules for uptake of the toxin (Schnepf et al. 1998; Gill et al. 1992). Other proteins (VIP proteins) are expressed during the vegetative growth phase of the bacterium. The Bt proteins are not toxic to vertebrates, which do not possess the necessary receptors for binding of the toxin. Herbicide resistance has been achieved for several products by introducing genes that encode an herbicide-­ insensitive target molecule, or an enzyme that degrades the herbicide (Sahora et al. 1998). The most widely deployed herbicide tolerance gene is one encoding a protein that allows plants to tolerate the herbicide, glyphosate, marketed under the trade name 32| Hector Quemada Roundup (James 2006; Brookes and Barfoot 2006). Glyphosate is a nonselective herbicide that has broad applications in many cropping systems. It is noted for its low environmental impact due to low toxicity to animals; rapid adsorption to soil particles, reducing movement in the environment; and rapid degradation by soil microbes (Cerdeira and Duke 2006). Genetically engineered virus resistance also has been developed for a few specialty crops with limited production areas, such as papaya and squash (Grumet 2002). In these cases a pathogen-­ derived resistance strategy has been used wherein the resistance genes are derived from the virus and expressed to interfere with the normal viral life cycle or trigger host defenses that target incoming viral RNA for degradation (Grumet and Lanina-­ Zlatkina 1996; Fuchs 2008). All products on the market thus far have obtained regulatory approval first in the United States, and a smaller number then have been submitted for regulatory approval in other countries. Slightly more than 100 transgenic products worldwide—­ representing 22 different species—­ have completed the necessary steps for commercial approval (Center for Environmental Risk Assessment n.d.; see also Fukuda-­Parr 2007). The various transgenic lines that have been approved have then been crossed to nontransgenic lines to create new hybrids or varieties that are locally adapted to conditions such as day length, local diseases, abiotic stresses, or speed of maturity, in order to create literally thousands of varieties. While a large number of genetically engineered transformation events have been approved, particularly in the United States, only a subset of them have been placed on the market, or continue to be on the market (Biotechnology Industry Organization 2010). For example, early entries into the market such as Flavr Savr tomatoes and NewLeaf potatoes are no longer sold or, in cases such as LL601 rice, have not been released commercially by the company that developed them. The reasons...