Could the Use of Genetically Engineered Crops Result in a Loss of Plant Biodiversity?

Food crops were first domesticated from wild species approximately 10,000 years ago when nomadic hunter-gatherers shifted to an agrarian lifestyle (1). Through human involvement in plant selection a profound effect was exerted on the genetic landscape, as plant species with favorable mutations were selected for propagation. Biodiversity in agroecosystems, which reflects not only species richness, but also the diversity of their interactions (2), continued to decline with changes in agricultural practices and plant breeding efforts, both of which focused on providing the high yields demanded by expanding populations (3, 4, 5). These negative effects on biodiversity, sometimes termed genetic erosion (6), also led to loss of weed species, killing of nontarget pests, and destruction of natural habitats for insects and wild animals (7). The larger the agricultural acreage, the greater the impact on surrounding flora and fauna.

Frankel (6) established principles of genetic erosion that describe agriculture’s impact on biodiversity: (a) during premodern agriculture, in centers of diversity, crop species were stable; (b) introduction of modern agricultural technologies, including new varieties, led to instability; (c) competition between local and introduced varieties led to displacement of local varieties; and (d ) displacing local varieties eroded genetic variability of regional crop populations. Plant breeding in the early 1960s produced high-yield varieties of major food crops, resulting in yield increases but also significant displacement of traditional varieties and a concomitant loss in genetic diversity, particularly landraces of cereals and legumes (8).

Recognition of this consequence on genetic diversity led to the development of global genebanks and collections to conserve genetic resources, such as those maintained by the USDA’s National Plant Germplasm System and the Consultative Group on International Agricultural Research (CGIAR). These collections, which preserve precious landraces and wild relatives, are the foundation of future classical breeding, marker assisted selection, and genetic engineering efforts and it is critical to maintain and enlarge these resources. Molecular and genomic technologies enable identification of genetic variants and development of detailed genetic descriptions of diversity, leading to greater appreciation of these resources. Information technology, which enables analysis of large data sets, has also led to advances in conservation and use of plant genetic resources.

The commercialization of herbicidetolerant (HT) and insect-tolerant (Bt) GE crops raised questions about the environmental and genetic conservation impacts of gene flow from GE crops to wild and weedy relatives. This gene flow could lead to selective advantages (e.g., enhanced invasiveness and/or weediness) of recipients in certain environments (9); this phenomenon is of particular interest in centers of crop diversity. Careful measures are needed when cultivating GE crops near such centers (8); however, this situation is not unique to GE plants and can and does happen with conventionally bred, commercialized crops (10). Key to judging the impact of transgene movement is the nature of the trait and the frequency of its introduction into an ecosystem. Studies of the impact of transgenes moving into wild relatives and the potential to change ecosystem dynamics are currently requested in environmental impact statements written for commercial release of a new GE plant (11). Although such tests are limited in scope and do not address all eventualities, they do provide insights into possible outcomes. Just as with other agricultural practices, certain impacts of GE crops on the environment need to be monitored, even after deregulation (see “Will the Widespread Use of Bt Crops Lead to the Development of Insect Resistance to Bt?”).

Another consideration regarding effects of GE crops on diversity of local, adapted crop varieties is that most current, commercial GE varieties were developed by large, mostly international companies. The few small seed companies remaining (12) have no legal access to GE traits, due in part to intellectual property (IP) issues (see “Why Are Genetically Engineered Crops Patented? Does This Affect Farmers in the United States?”). Thus it is difficult for these companies to move traits into local varieties, which leaves the task to larger companies. However, regulatory costs, IP, and other issues likely limit the numbers of varieties into which GE traits are moved by these companies, potentially narrowing the genetic base available to farmers.

References:

1. Tanksley S, McCouch S. 1997. Seed banks and molecular maps: Unlocking genetic potential from the wild. Science 277:1063–66

2. Nabhan GP. 2000. Native American management and conservation of biodiversity in the Sonoran Desert Bioregion: An ethnoecological perspective. In Biodiversity and Native America, ed. PE Minnis, WJ Elisens, pp. 29–43. Norman: Univ. Oklahoma Press

3. Angle JS. 1994. Release of transgenic plants: Biodiversity and population-level considerations. Mol. Ecol. 3:45–50

4. Ennos RA. 1997. The influence of agriculture on genetic biodiversity. Presented at Biodivers. Conserv. Agric. Br. Crop Prot. Counc. Symp. Proc. 69. Surrey, UK

5. Smart SM, Firbank LG, Bunce RGH, Watkins JW. 2000. Quantifying changes in abundance of food plants for butterfly larvae and farmland birds. J. Appl. Ecol. 37:398–414

6. Frankel OH. 1970. Genetic conservation in perspective. In Genetic Resources in Plants – Their Exploration and Conservation, ed. OH Frankel, E Bennett, pp. 469–89. Oxford: Blackwell

7. Millenn. Ecosyst. Assess. 2005. Ecosystems and Human Well-Being: Synthesis. Washington, DC: Island Press

8. Engels JMM, Ebert AW, Thormann I, de Vicente MC. 2006. Centres of crop diversity and/or origin, genetically modified crops and implications for plant genetic resources conservation. Genet. Resour. Crop Evol. 53:1675–88

9. Halfhill MD, Milwood RJ, Raymer PL, Stewart CN Jr. 2002. Bt-transgenic oilseed rape hybridization with its weedy relative, Brassica rapa. Environ. Biosaf. Res. 1:19–28

10. Ellstrand NC. 2006. Genetic engineering and pollen flow. Univ. Calif. Div. Agric. Nat. Resourc. Agric. Biotechnol. Calif. Ser. Publ. 8182.

11. Anim. Plant Health Insp. Serv., USDA. 2007. Introduction of genetically engineered organisms: Draft programmatic environmental impact statement-July. http://www.aphis.usda.gov/brs/pdf/complete_eis.pdf. Last accessed 2011-12-9. PDF

12. Fernandez-Cornejo J, Schimmelpfennig D. 2004. Have seed industry changes affected research effort? Amber Waves, Feb. 2004. http://www.ers.usda.gov/amberwaves/February04/Features/HaveSeed.htm. Last accessed 2011-12-9. PDF

Updated 2/16/12