[img_assist|nid=178|title=|desc=|link=none|align=right|width=100|height=43]The promise of more food from increased yields is driving the appeal for more GM crops, but that promise is theoretical and unfulfilled, argue Dr Ricarda A Steinbrecher and Antje Lorch.
Since the 1980s, biotechnology companies have promised that genetic engineering would produce crops that deliver higher yields. No such crop have ever been produced, but as fossil fuels supplies dwindle and food prices rise, the belief that higher-yielding GM crops could solve both our fuel and food problems has gained momentum and the prominence among policymakers, government officials and the media.
At present, such promises are little more than speculation. None of the existing GM crops in commercial cultivation is engineered specifically for yield increases. While it is claimed current crops that are engineered to be herbicide-tolerant or to produce insecticides yield more, this is not supported by independent field assessments. For some specific GM crops, reports even show lower yields.
The discussion is made more complex by the face that the terms ‘yield’ and ‘yield increase’ can mean different things in different agricultural systems. In monocultures, yield is generally defined as the amount of primary produce of the crop (the grain, for instance). Such a narrow definition ignores other products such as straw, which is useful as animal feed and bedding. In addition, one can distinguish between direct and indirect mechanisms of yield increase.
The kind of direct increases that could be gained are related to more biomass – in other words, to bigger oats or more or larger fruit. Indirect increases could be gained by changes in other characteristics that might make the crop perform better under adverse conditions (e.g. weed pressure and pest infestation). These ‘increases’ can more appropriately be described as ‘avoidance of loss or reduction’. For example, a GM herbicide-tolerant crop might produce an increase yield due to less competition from weeds as an indirect effect of a change in agricultural practices. If the weeds don’t pose a problem or are dealt with by other means, however, the GM trait is present in the crop without resulting in a yield increase.
[ The complete article is currently only available to subscribers of The Ecologist. ]