Co-existence between GM and non-GM crops: A case study on MON810 maize quantification

The contamination of a non-GM maize field by cross-fertilization with pollen from a neighbouring MON810 maize field was studied by sampling plants in a co-existence field test in Flanders. To accurately quantify GM percentages, an evaluation was performed of the effect of plant development stage. Sampling at different stages in the growth process of maize has indeed consequences for relative GM quantification based on haploid genome equivalents, due to the specific maize seed composition and differences in DNA extractability from different seed tissues. By sampling different maize plants and subparts at four different stages during the growth season, the evolution of weights, absolute DNA yields, DNA densities and the ratios of endosperm and embryo relative to the total maize kernel are studied in detail. During the plant growth, plant parts with potential GM genes (embryo in kernel and cob on total plant) increase in importance on weight as well as DNA concentration level, while the endosperm drops in relative importance. In order to determine the GM percentage in one kernel, the endosperm and embryo DNA content, relative to the total kernel DNA content are taken into account.
Based on these influencing factors, for the different sampling stages, expected % GM maize values are calculated for a whole (field) harvest of grain maize. This GM percentage on kernel level can further be extended to other maize usages in Flanders such as CCM (corn cob mix) and silage maize respectively, by taking into account the relative part (in weight) of grains to the total cob and of the total cob to the whole maize plant, respectively. In all calculations, it is assumed that complete cross-fertilization occurred of the non-GM field by the GM pollen coming from a surrounding field. In this context a model could be drawn for predicting the expected % GM (DNA) for lower overall (field- or harvest-based) GM admixture rates.