Sources of genetic diversity in feral oilseed rape (Brassica napus) populations

Abstract

Feral oilseed rape populations on roadsides and along other semi-natural habitats contribute to the uncertainty regarding the potential risk of transgene escape from genetically modified (GM) oilseed rape to wild or weedy populations. Knowledge about the underlying mechanism of establishment, persistence, and the evolutionary potential of feral populations is a prerequisite for a successful risk assessment and of high policy relevance. We analysed the origin, persistence, and genetic variation of feral oilseed rape populations in northwest Germany based on a field survey (2004-2007) and nuclear microsatellite markers. A maximum-likelihood approach was used to allocate individuals of feral populations to their source varieties and to hybrids between these varieties. The majority (72%) of the analysed sites was inhabited by oilseed rape for at least 2 years. The proportion of feral populations setting seeds varied between years (30-48%) and was higher than in comparable studies. Within-population genetic diversity of feral oilseed rape populations was higher than that of the common grown varieties studied. Repeated escapes of different varieties and hybridisation between these varieties were identified as the most important sources of genetic variation in feral oilseed rape populations. Up to four different source varieties were identified in feral populations. The detection of three hybrids between different varieties indicates that feral oilseed rape populations may persist via self-recruitment. Our results highlight the evolutionary potential of feral oilseed rape populations and have consequences for approaches to regulate the coexistence of genetically modified and non-GM oilseed rape varieties in the same region. Feral populations may serve as stepping stones for intraspecific and interspecific gene flow and can promote persistence of transgenes outside cultivation. The likelihood of introgressive interspecific hybridisation depends on the abundance of crossing partners, which may vary strongly from region to region. (C) 2009 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.