UNIVERSITE DE BOURGOGNE THÈSE Yongbo LIU - Université de ...

Introduction
The invasion of transgenic plants and transgenes into wild populations is a major biosafety
issue linked to the release of genetically modified (GM) plants, most notably for oilseed rape,
cotton, maize, sunflower, and soybean (Pilson, & Prendeville, 2004; Snow et al., 2005). For
many crops, spontaneous hybridization allows transgenes to spread to wild/weedy populations
of r elated t axa t hat o ccur n earby ( Ellstrand et al ., 1999). N umerous s tudies s upport t he
hypothesis th at h ybridization is a n in vasiveness s timulus ( in r eview b y E llstrand &
Schirenbeck, 2000), a lthough pl ant a daptation doe s not g uarantee s ubsequent i nvasion.
Transgenic crops or hybrids and backcrosses can escape from the field and establish in other
habitats as volunteer or feral plants via both pollen- and seed-mediated gene flow (Crawley &
Brown, 1995; 2004; Hall et al., 2000; Warwick et al., 2003; Knispel et al., 2008).
Long-term p ersistence o f v olunteer an d feral p lants, GM s eeds, an d crop al leles can
occur in fields. In Canada, one introgressed, glyphosate-resistant individual of Brassica rapa
was detected four years after the last GM oilseed rape (B. napus) was grown on the field, even
in the absence of glyphosate selection pressure (Warwick et al., 2008). Transgenic wild plants
were found three years after accidental escape of pollen and seeds from transgenic creeping
bentgrass (Agrostis stolonifera) in the USA (Zapiola et al., 2008). Herbicide-tolerant oilseed
rape seedlings emerged ten years after a field trial conducted in 1995, confirming the long-
term persistence of transgenic seeds in the seed bank in Sweden (D’Hertefeldt et al., 2008).
Multi-herbicide-resistant oilseed rape volunteers were found five to eight years after the last
GM cu ltivar was grown as p art o f a m ulti-year farm-scale s tudy i n France (Méssean et al.,
2007). In a recent study, Snow et al. (2010) found that crop-specific alleles persisted for ten
years in four weedy populations of hybrids between wild radish (Raphanus raphanistrum) and
R. sativus, suggesting that neutral or even detrimental genes can quite often persist in the wild.
Though t hese s tudies s how t hat t ransgenes c an invade a nd p ersist i n c rop vol unteers a nd
wild/weedy populations, there are few studies of the dynamics of the invasion process and the
impact on popul ations ( Ramachandran et al ., 2000; S utherland et al ., 2006; D amgaard &
Kjaer, 2009).
Several studies have demonstrated that the Bt-transgene for insect resistance in oilseed
rape confers hi gh relative f itness i n response t o i nsect he rbivory (Stewart et al ., 1997;
Ramachandran et al., 2000; Letourneau & Hagen, 2009). In the absence of selection pressure,
100