EVALUATING THE EFFECTIVENESS OF ISOLATION DISTANCES FOR FIELD PLOTS OF OILSEED RAPE (BRASSICA-NAPUS) USING A HERBICIDE-RESISTANCE TRANSGENEAS A SELECTABLE MARKER

The effectiveness of 200- and 400-m isolation distances were evaluated for small-scale trials of oilseed rape (Brassica napus L.). These dis tances have been used for previous transgenic release experiments and are commonly adopted for production of basic and certified breeders se ed. A 400-m(2) donor plot contained plants with a dominant transgene c onferring resistance to the herbicide glufosinate-ammonium. This chara cter was used as a selectable marker to measure the frequency of hybri d formation in 400-m(2) target plots of non-transgenic rape. Seeds pro duced by the non-transgenic plants were permitted to fall onto the plo ts and allowed to germinate. At the first true-leaf stage, the plants ware sprayed with glufosinate-ammonium. Surviving plants were respraye d, and a subsample assayed for the presence of the transgene using a c olorimetric assay and Southern-blot analysis. The average frequency of hybridization over two replicates was 0.0156% at 200 m and 0.0038% at 400 m. These estimates are within the limits established for the prod uction of basic seed (0.1%). Results indicated that bees were the most likely agent for long-distance pollen dispersal.