New Agronomy for Transgenic Crops?.

New transgenic traits can be classified in four categories: (1) pest or herbicide resistance, (2) altered composition for specific end uses, (3) greater resource acquisition [e.g. nutrients, water], (4) increased tolerance of abiotic stress. New pest or herbicide resistance traits will require management strategies that avoid resistance build up—similar to deployment options currently used for Bt and GHT crops. At issue is whether existing options are adequate. While Bt resistance seems to be in check, increasing numbers of glyphosate-tolerant weed species suggest improved deployment options are needed for widespread use of GHT crops. Compositional traits will likely require management modifications to optimize expression of the trait and post-harvest handling to assure identity preservation—similar to what farmers already do to produce and market high quality bread wheat using non-transgenic cultivars. For category 3 it will be argued that there is relatively small potential for genetic improvement in efficiencies of nutrients and water acquisition and use—at least for major cereal crops. The key to effective use of category 4 transgenics is not in modification of management practices per se, but rather in accurate identification of environments where their use gives greater profit and less risk than cultivars without such traits. It is difficult to develop “tradeoff-free” cultivars with tolerance of water deficit, flooding, heat, cold, or salinity. Hence, it is not likely such cultivars can perform better than best available cultivars in stress environments without yield penalties when grown with little or no stress. Use of climate and soil data and crop simulation models will be pivotal for identifying target environments for category 4 traits. Industry agronomists and seed dealers must become proficient in use of these tools. In some cases category 4 traits can lead to environmental degradation, which must be avoided.