The potential for dispersal of herbicide tolerance genes from genetically-modified, herbicide-tolerant oilseed rape crops to wild relatives

Abstract

1. The commercial growing of genetically modified, herbicide-tolerant (GMHT) oilseed rape is seen to result in the potential for the inserted gene to escape from the crop and become incorporated in the genomes of one or more related wild crucifer species, potentially giving a competitive advantage to the recipients. 2. The possibility of such gene transfer may be greatest where the wild relative is closely related to the crop, where the two grow in close proximity and where they flower at the same time. 3. Because oilseed rape is grown as either a winter-sown or a spring-sown crop, there are two flowering periods; winter rape in late March to mid-May and spring rape in June. There may be a short overlap period when some individuals in both crops are in flower at the same time. The existence of these two flowering periods extends the period over which both crop and wild relatives may be in flower together. 4. The most closely related species to oilseed rape (Brassica napus), and those which have been considered as potential recipients of herbicide tolerance are other members of the genus Brassica: B. oleracea, B. rapa, B, nigra, together with Raphanus raphanistrum and R. sativus, and two species of Sinapis, S. arvensis and S. alba. 5. As an adjunct to the Farm Scale Evaluations of GMHT oilseed rape, DEFRA funded a three-year project to examine the extent to which transfer of herbicide tolerance from the oilseed rape crops to wild relatives in the vicinity did occur. This report details the result of that study. 6. Transfer of herbicide tolerance was assessed in the field and in the laboratory. In the field, plants were tested by the application of a small quantity of glufosinate ammonium (LibertyTM) to individual leaves and observing whether any necrosis resulted. Seed collected from plants growing in or near oilseed rape fields were germinated and the resulting seedlings were sprayed with Liberty(TM) to assess tolerance. Any plants showing signs of tolerance to the herbicide were subjected to PCR to identify whether the gene was present. 7. The most common wild relative found in fields in the trial was Sinapis arvensis. In contrast, Brassica rapa was only found adjacent to a single field