FREQUENCY AND DISTANCE OF POLLEN DISPERSAL FROM TRANSGENIC OILSEED RAPE (BRASSICA-NAPUS)

The objective of this study was to evaluate pollen dispersal in Brassi ca napus (oilseed rape). The selectable marker, used to follow pollen movement, was a dominant transgene (bar) conferring resistance to the herbicide glufosinate-ammonium. Transgenic and non-transgenic plants o f the cultivar Westar were planted in a 1.1 ha field trial, with the t ransgenic plants in a 9 m diameter circle at the centre, surrounded by non-transgenic plants to a distance of at least 47 m in all direction s. A 1 m circle of non-transgenic plants was sown in the centre of the transgenic area to allow estimation of the level of pollen dispersal when plants were in close contact. Honeybee hives were placed at the t rial site to optimize the opportunity for cross-pollination. During th e flowering period, regular observations were made of the number of pl ants flowering and the number and type of insects present in 60 1 m(2) areas. These areas were located uniformly around the plot at distance s of 1, 3, 6, 12, 24, 36 and 47 m from the edge of the 9 m circle of t ransgenic plants. Seed samples were harvested from each of the 7 dista nces so that approximately 20% of the circumference of the plot was sa mpled at each distance. The centre non-transgenic circle was also samp led. Plants were grown from the seed samples and sprayed with glufosin ate to estimate the frequency of pollen dispersal at each distance. In order to screen enough samples to detect low frequency cross-pollinat ion events, seed samples were tested in the greenhouse and on a larger scale in the field. Results were confirmed by testing progeny for glu fosinate resistance and by Southern blot analysis. The estimated perce ntage of pollen dispersal in the non-transgenic centre circle was 4.8% . The frequency was estimated to be 1.5% at a distance of 1 m and 0.4% at 3 m. The frequency decreased sharply to 0.02% at 12 m and was only 0.00033% at 47 m. No obvious directional effects were detected that c ould be ascribed to wind or insect activity.