DO BARREN ZONES AND POLLEN TRAPS REDUCE GENE ESCAPE FROM TRANSGENIC CROPS

As genetically engineered crop varieties near widespread cultivation, both agronomic and environmental concerns mandate the development of e ffective strategies for isolating transgenic varieties from related no n-transgenic varieties or cross-fertile weeds. We present the results of the first field experiment designed to test the effectiveness of tw o containment strategies that are commonly used in field trials of tra nsgenic crops: (1) an isolation zone devoid of vegetation to discourag e emigration of insect pollinators from transgenic plots; and (2) trap crops (non-transgenic varieties of the same crop planted adjacent to the transgenic plot that can ''cleanse'' emigrating pollinators of tra nsgenic pollen). In conjunction with field trials of genetically engin eered canola (Brassica napus) conducted by Calgene, Inc., in Californi a and Georgia, we varied both the width of the barren zone and the pre sence or absence of a trap crop, and measured the effects on gene esca pe. Escape was easily detected since the genetic construct inserted in to the transgenic canola contained a gene that rendered seedlings resi stant to the normally lethal antibiotic kanamycin. Our results suggest that barren zones 4-8 m in width may actually increase seed contamina tion over what would be expected if the intervening ground were instea d planted entirely with a trap crop. When trap crops occupied a limite d portion of the isolation zone separating transgenic and non-transgen ic varieties, the effectiveness of the trap depended on the width of t he isolation zone: they reduced gene escape when the two varieties wer e separated by 8 m, but increased escape across a 4-m isolation zone. We conclude that, for the relatively short isolation distances we exam ined, the most effective strategy for reducing the escape of transgeni c pollen is to devote the entire region between transgenic and non-tra nsgenic varieties to a trap crop.