Genetically modified organisms (GMOs), alternatively called biotech crops, dominate soybean and cotton production and are rapidly increasing their fraction of market share for maize and rice in the U.S. Engineered canola is important in Canada, soybeans are dominant in Argentina and Brazil, and cotton is prominent in China and India. Adoption is much slower elsewhere, in large part due to concerns for potential ecosystem effects that may occur through development of weedy plants, by selection of herbicide resistant weeds and by effects of insecticidal proteins on nontarget insects. The precautionary principle is invoked by critics concerned that one must know in advance the effects of GMOs before releasing them. Alteration of weed species composition of agricultural fields is well documented to occur under herbicide selection pressure. Gene flow to wild relatives of crop plants can be shown under herbicide selection, and one instance (sunflower) is provided for insect resistance transfer leading to increased seed production by a weedy relative. Detailed stewardship programs have been developed by seed producers to minimize risks of gene flow. Although herbicides and insecticides are known to have major effects on agroecosystems, the ecosystem impacts of GMOs per se, thus far appear to be small.
Key words: gene-flow, herbicide-resistant weeds, genetically engineered crops, Bt maize, Roundup Ready soybeans
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