Gene flow from oilseed rape to weeds

Gene flow between transgenic crops and their wild relatives is a key issue for the scientific and public acceptance of genetically modified varieties. The results reported in this paper concern the assessment of F1 interspeci fic hybrid production and the analysis of the following generations. The su bjects of the studies were male sterile or male fertile herbicide tolerant oilseed rape cultivars (Brassica napus) and three weedy species largely spr ead in cultivated areas and presenting an overlapping flowering period. The se were hoary mustard (Hischfeldia incana), wild mustard (Sinapsis arvensis ) and wild radish (Raphanus raphanistrum). All the Fl interspecific hybrids were obtained except using wild mustard as the female but the rates of pro duction depends on the weed and on the conditions of production. Experiment s under normal agronomic conditions revealed a very low frequency of hybrid s. The Fl hybrids are vigorous but their low female fertility reduces their fitness. From oilseed rape-wild radish hybrids, we studied the four follow ing generations, under optimal conditions. We observed a reduction of the t ransgene transmission and of the chromosome number but an increase of the m ale and female fertility. However, none of the herbicide tolerant plants ha d the same chromosome number as the weed. Complementary experiments and str ategies for reducing the gene flow are presented and discussed.