THE IMPACT ON BIOSAFETY OF THE PHOSPHINOTHRICIN-TOLERANCE TRANSGENE IN INTER-SPECIFIC BRASSICA-RAPA X BRASSICA-NAPUS HYBRIDS AND THEIR SUCCESSIVE BACKCROSSES

There is strong evidence indicating that gene flow from transgenic B. napus into weedy wild relatives is inevitable following commercial rel ease. Research should now focus on the transmission, stability, and im pact of transgene expression after the initial hybridization event. Th e present study investigated the transfer of a phosphinothricin-tolera nce transgene by inter-specific hybridization between B. rapa and two transgenic B. napus lines. The expression of the transgene was monitor ed in the F-1 hybrids and in subsequent backcross generations. The tra nsgene was transmitted relatively easily into the F-1 hybrids and reta ined activity. Large differences in the transmission frequency of the transgene were noted between offspring of the two transgenic lines dur ing backcrossing. The most plausible explanation of these results is t hat the line showing least transmission during backcrossing contains a transgene integrated into a C-genome chromosome. Approximately 10% of offspring retained the tolerant trait in the BC, and BC, generations. The implications of these findings for the stable introgression of tr ansgenes carried on one of thp chromosomes of the C-genome from B. nap us and into B. rapa are briefly discussed.