Pest Spectrum Switch Documented for High-Lectin Potato
An attempt to make potato plants resistant to sap-sucking insects has demonstrated the potential for unexpected results. Since the B.t. toxin only deters consumption by lepidopteran species such as butterflies and moths, genetic engineers have been looking at other natural substances to keep insects at bay, such as theproteinaceous lectins found in many plants and seeds. Now a team at the Scottish Crop Research Institute (SCRI) has found that potato plants transformed with lectin genes have lower levels of bitter-tasting chemicals called glycoalkaloids that make plants unpalatable to many mammals and insects. Glycoalkaloid levels in the leaves of the lectin-transformed potatoes dropped by up to 44 percent. This seems to be due to the genetic modification (GM) technique itself, because introducing another type of gene, for another potential insect deterrent called cowpea trypsin inhibitor, also caused glycoalkaloid levels in the plants to drop substantially. The team warns that plants with lower glycoalkaloid levels could be more vulnerable to a range of insect pests, including the potato leafhopper. Additionally, reduced levels of the glycoalkaloid alpha-chaconine actually stimulate the potato aphid to feed.
While the potatoes were only experimental varieties, unexpected side effects have also turned up in commercial GM crops. The stems of a herbicide-resistant soybean were found to crack open in hot climates, for instance. However, unintended effects also occur in traditional breeding programs, points out Howard Davies of the SCRI. He adds that new techniques should help address the problem. "Technologies are now being developed to measure several hundreds, if not thousands, of metabolites in plants using metabolic profiling procedures." (New Scientist Weekly Newsletter No. 138, 6/1/02).
