Assessment of interspecific hybridization between transgenic oilseed rape and wild radish under normal agronomic conditions

In order to assess the hybridization rate between oilseed rape and wild radish under normal agronomic conditions, three 1-ha field experiments were performed. In each case, wild radish plants were transplant ed at different densities in the middle, the border, or the margin of the herbicide-tolerant oilseed rape field. Among the 189084 seedlings obtained from seeds harvested on wild radish plants, only one herbicide-tolerant interspecific hybrid (RrRrAC, 2n = 37) was characterized from seeds harvested on an isolated plant growing in the margin of the field. Thus, for the wild radish total harvest, with a 95% confidence limit, the frequency of interspecific hybrids was assessed to range from 10(-7) to 3.10(-5). Interspecific hybrids were detected in all cases among the smallest seeds with a diameter less than 1.6 mm harvested on oilseed rape, but the highest frequency was obtained from oilseed rape close to wild radish plants growing as clusters in the border or the margin of the field. Most hybrids had the expected triploid genomic structure (ACRr, 2n = 28) except for four amphidiploids (AACCRrRr, 2n = 56) and one hybrid from a wild radish unreduced gamete (ACRrRr, 2n = 37). Among the 73847 seedlings observed on the oilseed rape total harvest, the frequency of interspecific hybrids was assessed to range from 2.10(-5) to 5.10(-4), with a 95% confidence limit. The results are discussed with regard to the type of oilseed rape variety used and the characteristics of the interspecific hybrids.