Characterization of backcross generations obtained under field conditions from oilseed rape-wild radish F1 interspecific hybrids: an assessment of transgene dispersal

 Gene flow from glufosinate-resistant transgenic oilseed rape to wild radish was studied over two backcross generations. Under field conditions, seed production from oilseed rape-wild radish F1 hybrids due to pollination by wild radish was always low: on average 0.12 and 0.78 seeds per 100 flowers and per plant, respectively. The cytogenetics of the resulting «BC1» plants can be explained in the main by three different genomic constitutions: either ACRrRr, 2n=37, ACRr, 2n=28 (the same chromosome number as the mother plant), or by the amphidiploid AACCRrRr, 2n=56. The probability of gene exchange through chromosome pairing was high only in plants with 2n=28 or 37 chromosomes. Due to the viability of unreduced or partially reduced female gametes, most of the «BC1» plants (81.9%) were Basta resistant whereas the analysis of oilseed rape specific loci indicated that their transmission varied with the locus. In spite of low male fertility (8.7%), an improvement of the female fertility over the F1 hybrids was observed with an average production of 1.4 and 11 seeds per 100 flowers and per plant, respectively. At the following «BC2» generation, the bar gene transmission (57.2% of Basta-resistant plants) decreased as did the chromosome number, with a majority of plants having between 24 and 27 chromosomes, with 10.5% similar to wild radish (2n=18). The lower the chromosome number, the better the fertility of the «BC2» plants. On average, 7.9 and 229.3 seeds per 100 flowers and per plant were produced. Gene-flow assessment is discussed based on these data.