Overwintering of genetically modified sugar beet, Beta vulgaris L. subsp vulgaris, as a source for dispersal of transgenic pollen

The potential impact of transgenic crops on community ecology will depend o n the distribution and establishment of the new transgenic traits, on the s exual transfer of their new genes to the environment (Bartsch & Pohl-Orf, 1 996) and on the potential ecological impact of the transgenic trait. Flower ing and pollen dispersal is important for outcrossing of the genetically en gineered trait. For a biennial plant, like the cultivars of Beta vulgaris L ., overwintering is normally necessary to become generative and to produce pollen and seeds (Abe et al., 1997), which usually does not happen with sug ar beet as a field crop harvested in autumn (Longden 1989). The starting po int for the project was a transgenic sugar beet, Beta vulgaris L. subsp. vu lgaris (Lange et al., 1998), with rhizomania and herbicide (Basta (R), Libe rty (R)) resistance. Cold tolerance is one of the most important factors fo r survival of sugar beet in Central- and North-Europe. Among other ways, sp reading of transgenic traits into weed beet (Boudry et al., 1993) or wild b eet can occur if genetically engineered - biennial - plants survive the win ter, flower in spring and spread their pollen. Field experiments were perfo rmed with transgenic breeding lines and their hybrids, transgenic and non-t ransgenic hybrids with Swiss chard and three conventional beet cultivars to evaluate winter survival rates at seven different field sites. We could sh ow that survival of sugar beet - transgenic as well as conventional ones - in Germany and at the Dutch border is possible. Survival rates were well co rrelated with temperature data and were unexpectedly high. Differences betw een sugar beet hybrids and breeding lines could be detected but not within different breeding lines or hybrids. There were no differences detectable b etween transgenic and non-transgenic plants. The data are crucial for the r isk assessment of the release of transgenic sugar beet and are the basis fo r further experiments towards outcrossing and establishment.