With the extensive adoption of transgenic crops, an understanding of transgene flow isessential to manage gene flow to non-GM crops. Thus, a flexible and accurate numericalmodel is required to assess gene flow through pollen dispersal. A three-dimensionalatmospheric model combined with a diffusion transport model would be a useful tool forpredicting pollen dispersal since it would be flexible enough to incorporate the effectsof factors such as the spatial arrangement of crop combinations, land use, topography,windbreaks, and buildings. We applied such a model to field measurements of gene flowbetween two adjacent maize (Zea mays) cultivars, with suppression effectsdue to windbreaks, in an experimental cornfield in Japan. This combined model reproducedthe measured cross-pollination distribution quite well in the case of maize plots withplant windbreaks slightly taller than the maize and without windbreaks, but the modelunderestimated the effect of a 6-m-tall windbreak net beyond 25 m from the donor pollensource on cross-pollination. The underestimation was most probably due to the problem ofassimilated wind data. The model showed that the 6-m-tall windbreak and the plant windbreak suppressed average cross-pollination rate by about 60% and 30%, respectively.Half-tall and coarser mesh windbreak net suppressed cross-pollination rates by 40% byreducing the swirl of donor pollen by reduced wind speed.

Plant to plant gene flow is a route of environmental exposure for GM plants specifically since crosses with wild relatives could lead to the formation of more vigorous hybrids, which could increase the rate of introgression and the environmental impact. Here, we test the first step in the process of potential transgene introgression: whether hybrid vigor can be inherited to the next generation, which could lead to fixation of altered, i.e., elevated, quantitative traits.

The potential for a permanent elevated fitness was tested using individual autogamous progeny lineages of hybrids between the crop Lactuca sativa (Lettuce) and the wild species Lactuca serriola (Prickly Lettuce). We compared progeny from motherplants grown under either greenhouse or field conditions. The survival of young plants depended strongly on maternal environment. Furthermore, we observed that offspring reproductive fitness components were correlated with maternal fitness.

Our study demonstrates that post-zygotic genotypic sorting at the young plants stage reduces the number of genotypes non-randomly, leading to inheritance of high levels of reproductive traits in the surviving hybrid lineages, compared to the pure wild relatives.

Consequently, directional selection could lead to displacement of the pure wild relative and fixation of more vigorous genome segments originating from crops, stabilizing plant traits at elevated levels. Such information can be used to indentify segments which are less likely to introgress into wild relative populations as a target for transgene insertion.

Genetically modified (GM) maize expressing the insecticidal protein Cry1Ab from Bacillus thuringiensis (Bt maize) is the only GM crop planted commercially in the European Union (EU). Cultivation in accordance with Directive 2001/18/EC demands post-market environmental monitoring (PMEM) to ensure the detection and prevention of adverse effects on the environment possibly deriving from commercial cultivation. Based on a seminar organized in Berlin, Germany, in April 2008 by the EU-funded Biosafenet project, the present paper reflects on experiences and hurdles faced during the implementation of PMEM for Bt maize. It reviews and reconsiders PMEM programs of Bt maize in view of existing experiences from cultivation, current monitoring activities initiated by Member States and applicants, proposed monitoring strategies and methods as well as potential environmental impacts of cultivation. Future challenges will arise from large-scale and cumulative cultivation of various events. This will demand optimized organization structures for data collation and integration to support further decision-making and management.