title: Locus-dependent selection in crop-wild hybrids of lettuce under field conditions and its implication for GM crop development.
abstract: Gene escape from crops has gained much attention in the last two decades, as transgenes introgressing into wild populations could affect the latter's ecological characteristics. However, different genes have different likelihoods of introgression. The mixture of selective forces provided by natural conditions creates an adaptive mosaic of alleles from both parental species. We investigated segregation patterns after hybridization between lettuce (Lactuca sativa) and its wild relative, L. serriola. Three generations of hybrids (S1, BC1, and BC1S1) were grown in habitats mimicking the wild parent's habitat. As control, we harvested S1 seedlings grown under controlled conditions, providing very limited possibility for selection. We used 89 AFLP loci, as well as more recently developed dominant markers, 115 retrotransposon markers (SSAP), and 28 NBS loci linked to resistance genes. For many loci, allele frequencies were biased in plants exposed to natural field conditions, including over-representation of crop alleles for various loci. Furthermore, Linkage disequilibrium was locally changed, allegedly by selection caused by the natural field conditions, providing ample opportunity for genetic hitchhiking. Our study indicates that when developing genetically modified crops, a judicious selection of insertion sites, based on knowledge of selective (dis)advantages of the surrounding crop genome under field conditions, could diminish transgene persistence.
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam Amsterdam, The Netherlands ; Centre for Ecology and Hydrology Wallingford, UK.
authors.forename: Danny A P
authors.initials: DA
authors.lastname: Hooftman
authors.affiliation: University of Dundee at SCRI Dundee, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Flavell
authors.affiliation: Biometris Wageningen UR, Wageningen, The Netherlands.
authors.forename: Hans
authors.initials: H
authors.lastname: Jansen
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam Amsterdam, The Netherlands.
authors.forename: Hans C M
authors.initials: HC
authors.lastname: den Nijs
authors.affiliation: University of Dundee at SCRI Dundee, UK.
authors.forename: Naeem H
authors.initials: NH
authors.lastname: Syed
authors.affiliation: Keygene N.V Wageningen, The Netherlands.
authors.forename: Anker P
authors.initials: AP
authors.lastname: Sørensen
authors.affiliation: Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam Amsterdam, The Netherlands ; Keygene N.V Wageningen, The Netherlands.
authors.forename: Pablo
authors.initials: P
authors.lastname: Orozco-Ter Wengel
authors.affiliation: Wageningen UR Plant breeding Wageningen, The Netherlands.
authors.forename: Clemens C M
authors.initials: CC
authors.lastname: van de Wiel
keywords: Lactuca; crop breeding; gene flow; genetic modifications; hitchhiking; introgression; linkage disequilibrium; transgenic plants