Because of the increasing use of maize hybrids with genetically modified (GM) stacked events, the established and commonly used bulk sample methods for PCR quantification of GM maize in non-GM maize are prone to overestimate the GM organism (GMO) content, compared to the actual weight/weight percentage of GM maize in the grain sample. As an alternative method, we designed and assessed a group testing strategy in which the GMO content is statistically evaluated based on qualitative analyses of multiple small pools, consisting of 20 maize kernels each. This approach enables the GMO content evaluation on a weight/weight basis, irrespective of the presence of stacked-event kernels. To enhance the method's user-friendliness in routine application, we devised an easy-to-use PCR-based qualitative analytical method comprising a sample preparation step in which 20 maize kernels are ground in a lysis buffer and a subsequent PCR assay in which the lysate is directly used as a DNA template. This method was validated in a multilaboratory collaborative trial.
The Bt11 maize-specific qualitative detection method based on polymerase chain reaction (PCR) in the JAS analytical test handbook has been widely used for administrative monitoring of GM crops and quality control of commercially distributed grains. In the present investigation, some apparently false-positive detections were observed in assays using the Bt11 maize-specific method, and these erroneous results were proved to have been caused by non-specific DNA amplification. We improved the detection method to reduce non-specific amplification by decreasing the concentration of magnesium ions in the PCR mixture. The subsequent evaluation of analytical performance demonstrated no marked di#erence between the currently used and the improved methods, except for the reduced non-specific amplification. We conclude that the currently used standard method should be replaced with the improved method for the reliable detection of Bt11 maize.
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