PCR-based quantification of genetically modified Bt maize: single-competitive versus dual-competitive approach

Methods for the quantification of transgenic insect-resistant Bt maize by single- and dual-competitive PCR were developed. The analysis of mixtures of DNA solutions, as well as of maize flours containing defined amounts of Bt maize, demonstrated the usefulness of single-competitive PCR based on coamplification of the CDPK promoter/cry1A(b) gene region of Bt maize and an internal standard. Upon heat treatment of DNA solutions and maize flour, respectively, the recovery of the Bt proportion compared to the starting material determined by single-competitive PCR decreased significantly. This systematic error could be compensated for by using a dual-competitive approach based on PCR quantification of the transgenic target sequence of Bt maize and of the maize specific invertase gene (ivr1).