Cultivation of GE Oilseed Rape with Different Herbicide Resistances

Oilseed rape (Brassica napus L.) engenders special concern regarding gene flow, due to its potential for outcrossing, for volunteer emergence and to form temporary feral populations. If different genetically engineered (GE) herbicide-resistant oilseed rape cultivars are grown in neighboring fields, seeds and subsequent volunteers with multiple herbicide resistances (HR) can arise.1 If multiple resistant volunteer plants are not removed, e.g., by using an appropriate herbicide, they can serve as a source or sink for further cross-pollination.2 In addition to potential problems with multiple resistant volunteers following crop rotations, the combination (´stacking`) of different GE traits in one plant may affect HR gene expression and thereby the reliability of expression-based transgene detection. In a recent paper,3 we presented the results of a biennial large-scale field experiment with two different GE oilseed rape lines cultivated on adjacent plots to investigate the frequencies of HR gene dispersal, the expression of HR genes in double-resistant plants, and the sensitivity of plants to conventional herbicides. Adventitious Presence of Transgenes in the Seed Harvest Field experiments with GE winter oilseed rape consisted of two double plots of 1 ha each in which glufosinate-ammonium resistant (LibertyLink; LL) plants and glyphosate resistant (Roundup Ready®; RR) plants were grown side by side, separated either by 0.5 m or by 10 m isolation distance. Seeds were sampled along 2 m wide sampling strips located at 0, 10, 20, 40 and 70 m within each plot. Samples were analyzed by phenotypic herbicide germination tests and by specific polymerase chain reactions (PCR). The design of the field experiments not only allowed determination of mutua