Quantitative GMO detection in maize (Zea mays L.) seed lots by means of a three-dimensional PCR based screening strategy

Due to the preparation of new EU legislation on the adventitious and unavoidable presence of genetically modified seeds in conventional seed lots, quantification of the contamination of conventional seed lots is becoming more and more important. Nowadays quantification is performed by real-time PCR or by statistically based sub-sampling strategies. Due to the fact that both techniques imply the grinding and homogenisation of a sample, specific properties and characteristics of seeds that are important for quantification are lost. In some cases information is required on the number of transgenic seeds, the zygosity or the identity of the contaminants. For these purposes we propose an alternative method for quantification based on a combination of a three-dimensional pooling of seeds and a qualitative PCR based screening strategy. The identification of a single transgenic seed among a population of 1000 requires no more than 30 PCR reactions; one for each column (10), row (10) and block (10). The window between which quantification is possible lies between 0% GMO and 0.9% GMO which covers the labelling thresholds of 0.3%, 0.5% and 0.7% proposed by the EU.