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

Introduction
One potential risk that is associated with commercial release of transgenic crops, most notably
canola a nd c otton, i s t ransgene f low b etween c rops a nd t heir w ild r elatives ( Pilson &
Prendeville 2004) . E llstrand et a l. (1999) reviewed t hat 12 out of t he w orld’s 13 m ost
important c rops could h ybridize w ith wild r elatives, s uggesting t ransgene c ould escape vi a
spontaneous hybridization with and introgression to wild relatives, even though this full list
has n ot b een realized (Stewart et al. 2003). The escape o f transgenes into wild populations
could e nhance t he w eediness or t he i nvasion of ne w h abitats, s ince t he t ransgenes pr ovide
adaptive t raits s uch as resistance t o p ests, h erbicides, d iseases an d v arious en vironmental
stresses ( Darmency 1 994). V olunteers a nd h ybrids w ere obs erved a groecosystems t ogether
with sown crops and in their neighborhoods (Knispel et al. 2008; Warwick et al. 2008), and
one of the causes was the occurrence of gene flow via pollen dispersal (Hall et al. 2000).
Generally, gene flow can occur mainly via pollen and seed. Although more attention has
been pa id t o t he pot ential of pol len di spersal, t he i ntentional m ovement of s eed dur ing
harvesting, transportation and commerce may be of greater importance for the long-distance
dispersal of t ransgenes. Seed l oss c an oc cur b ecause of t he pods s hattering be fore- and/or
post-harvest op eration. The s maller t he s eed, t he greater t he r isk of gene flow i s t hrough
dispersal m echanism b y w ind, a nimals or hum an a ctions. A ctually, m ost h ybrids b etween
oilseed rape (OSR, Brassica napus) and wild relatives produce a plethora of small seeds (Eber
et a l. 1994; C hadoeuf et a l. 1998; W ei & D armency 2008 ). S ome s tudies s howed t hat
interspecific hybrids are present only among seeds with a diameter less than 1.6 mm (Eber et
al. 1994; Baranger et al. 1995; Chèvre et al. 2000). For example, most crosses between OSR
and wild relatives such as B. juncea (Bing et al. 1996), B. rapa (Jørgensen & Andersen 1994),
Hirschfeldia i ncana and Raphanus r aphanistrum (Eber et a l. 1994; C hadoeuf et a l. 1998)
only produced small seeds. Wei and Darmency (2008) found all hybrid seeds formed between
a ma le s terile OSR c ultivar a nd f our w ild s pecies w ere s mall. It w as s uggested th at s mall
seeds would result in a fitness disadvantage since seed mass would affect the emergence and
initial seedling size (Aparicio et al. 2002; Westoby et al. 2002). Subsequent decrease of plant
fitness of small-seeded plants might be exacerbated unde r stressful conditions such as hi gh
density, shade, drought or herbivory (Gardner & Vanderlip 1989; Verdu & Traveset 2005).
Thus, the hypothesis was proposed that gene flow might be hampered by small seed size of
hybrids between transgenic crops and wild relatives (Wei & Darmency 2008). In that paper
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