Quantifying Gene Flow from Oilseed Rape to Its Wild Relatives

EXTENDED ABSTRACT Gene flow is defined as the movement of genes between populations and is a naturally occurring phenomenon among sexually compatible individuals. Crops have exchanged genes with their wild and weedy relatives for centuries, however this process has recently caused concern. The rapid advances in genetic engineering have hit an immense wall of opposition and gene flow is now seen as a possible escape route for transgenes. The safety of genetically modified (GM) crops has been fervently debated and the possible risks, to both the consumers of the crops and to the environment, have prevented their commercialisation in Britain and many other countries. Concern has arisen that if detrimental effects were to be detected post release of any GM crop, withdrawal may be difficult, or impossible, if gene flow has already occurred. Other potential, undesirable consequences of gene flow are the evolution of increased weediness and the extinction of wild relatives. It is thought that crop to wild gene flow has caused increased weediness in seven wild relatives of the world's thirteen most important crops and extinction in two (Ellstrand et al. 1999). Gene flow can only prove a substantive risk if suitable recipients grow sympatric to the GM crop (i.e. in the same geographic location), if the transgene combines stably within the recipient to form a fertile hybrid and if the fitness of the hybrids is not reduced to a deleterious extent. In the UK more than ten crops have been found to spontaneously hybridise with one or more elements of the local flora (Raybould & Gray, 1993). Oilseed rape provides an example of one of these crops and is a useful species for modelling gene flow. Within Britain the species of rape that is grown commercially for oilseed is Brassica napus, a hybrid between Brassica rapa and Brassica oleracea. Both of these parent species grow wild throughout Britain, with B.rapa growing exclusively on riverbanks and B.oleracea at a few known coastal sites (Rich, 1991; Mitchell &Richards, 1979). There are two planting times for oilseed rape in Britain, winter and spring and it has been found that the winter-sown variety flowers concurrent to B.rapa whereas the spring-sown variety flowers later. However, due to the long flowering period of the wild species there can be some overlap with the flowering of spring-sown rape and low rates of hybridisation may be possible (Jorgensen & Anderson, 1994). It is widely believed …