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Introduction
Plant divergence is generated by isolation by distance (genetic drift) or by changes in mating
systems and adaptation driven via natural selection (Hey 2006; Ross-Ibarra et al. 2009; Zheng
and G e 2010) . In c ontrary, gene f low pl ays a ke y r ole i n m aintaining c ohesion a mong
geographically s eparated popul ations a nd m akes s pecies t o e volve a s uni tes ( Morjan and
Rieseberg 2004; Abbott and Comes 2007; Hey 2006; Nosil 2008). Introgression of wild plants
by genes from crops could result in poor divergence when gene flow is strong enough, with
no correlation b etween genetic d ifferences and geographic d istances (Kercher a nd C onner
1996; Sahli et al. 2008).
Although it is a natural phenomenon associated to crop development, gene flow and
introgression f rom c rops to th eir w ild r elatives r eceive n ow in creasing a ttention in th e
framework of the commercial release of genetically modified (GM) crops. Because GM crops
confer new traits, such as resistance to insects, herbicides and diseases, they could result in
undesired consequences of e ventual t ransgene i ntrogression t hrough t he di spersal of
interspecific h ybrids and their progeny. Introgression after hybridization between GM crops
and their wild relatives may result in increasing: (1) genetic variation that promotes adaptive
evolution ( Rattenbury 1 962; P ostma a nd V an N oordwijk 2005), ( 2) weediness of w ild
species ( Darmency 199 4; P ilson a nd P rendeville 2004) , ( 3) c ompetitiveness or c olonizing
abilities through hybrid vigor or new traits (Ellstrand et al. 1999; Ramachandran et al. 2000),
(4) i nvasiveness vi a e nhanced f itness ( Vacher et a l. 2004) , a nd ( 5) a bility t o m atch new
environment (Campbell et al. 2006; Whitney et al. 2006), which eventually could result in the
displacement o f n atural c ommunity e quilibriums, in cluding th e elimination o f d esirable
species through competition (Tiedje et al. 1989).
Several studies have found long-term introgression from crops to their wild relatives,
such as in rice (Suh et al. 1997), radish (Snow et al. 2001; Hedge et al. 2006), oilseed rape
(Hansen et al. 2001) and sunflower (Whitton et al. 1997; Linder et al. 1998). The crop-wild
introgression ma y a lter morphological a nd lif e history tr aits a s w ell as th e e volutionary
trajectory of w ild popul ations ( Lee a nd S now1998; S now e t a l. 2001; Lenormand 2002;
Campbell e t a l. 2009a ), w hich c ould l ead t o popul ations e xhibiting pe culiar t raits a nd
population dynamics. In addition, local natural selection exerted on new genetic backgrounds
could make introgressed wild populations to converge to or diverge from their parental taxa,
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