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 F-1 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 Zn = 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 F-1 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.