ASSESSMENT OF DNA EXTRACTION METHODS FROM VARIOUS MAIZE (Zea mays L.) TISSUES FOR ENVIRONMENTAL GMO MONITORING IN MEXICO. PART I: DETECTION BY END-POINT PCR

In Mexico, regulations for growing genetically modified (GM) maize (Zea mays L.) plants have been enforced in order to prevent gene flow to native landraces and wild relatives. Field surveys are necessary and Mexican government agencies have the mandate to perform them. Because of their specificity, PCR-based methods are suitable for field monitoring of GM organisms but it is necessary to assess their performance, since they are greatly influenced by the DNA preparation quality inherent to the extraction method. In this study, genomic DNA was extracted from various maize tissues (e.g. pollen, leaves, spikelets and grains) using five different commercial purification protocols. DNA quality was analyzed spectrophotometrically, by gel electrophoresis, and as a substrate for end-point PCR. Results showed that highly amplifiable DNA, rather than high extraction yields, is needed for a consistent analysis. Criteria to evaluate DNA purity, such as absorbance, do not necessarily reflect an adequate amplification capability, resulting in a non-reliable GM organism detection. In conclusion, silica DNA-binding membranes yielded the most suitable DNA preparations for end-point PCR analyses of different GM maize tissues.