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 rad ish under normal agronomic conditions, three 1-ha field experiments were pe rformed. In each case, wild radish plants were transplant ed at different d ensities in the middle, the border, or the margin of the herbicide-tolerant oilseed rape field. Among the 189084 seedlings obtained from seeds harvest ed on wild radish plants, only one herbicide-tolerant interspecific hybrid (RrRrAC, 2n = 37) was characterized from seeds harvested on an isolated pla nt growing in the margin of the field. Thus, for the wild radish total harv est, with a 95% confidence limit, the frequency of interspecific hybrids wa s assessed to range from 10(-7) to 3.10(-5). Interspecific hybrids were det ected in all cases among the smallest seeds with a diameter less than 1.6 m m harvested on oilseed rape, but the highest frequency was obtained from oi lseed 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 st ructure (ACRr, 2n = 28) except for four amphidiploids (AACCRrRr, 2n = 56) a nd one hybrid from a wild radish unreduced gamete (ACRrRr, 2n = 37). Among the 73847 seedlings observed on the oilseed rape total harvest, the frequen cy 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 interspec ific hybrids.