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

INTRODUCTION
Genetically modified (GM) plants can hybridize spontaneously with wild or weedy relatives
(Ellstrand e t a l. 1999) , which has t riggered co ncern about t he f ate o f t ransgene escapes.
Transgenes c ould s pread a nd pe rsist i n s tands of w ild r elatives t hrough t ransgenic h ybrids
backcrossing w ith w ild pl ants. T wo i mportant f actors de termining t he l ikelihood of t his
occurrence are i) the initial invasion and persistence of the transgene in wild relatives stand
and, i i) c ompetition of t ransgenic h ybrids w ith t heir ne ighbors ( Hauser et a l. 1998) . M any
transgenes i nducing a c ommercially b eneficial t rait t o cr ops, s uch as herbicide o r i nsect
resistance, may also bring benefits in weeds. In contrast, a fitness cost may be caused by the
transgene expression in terms of resource allocation and also by interspecific h ybridization.
Several s tudies h ave d etected f itness ef fects o f t he t ransgene when i ntroduced i nto
populations of wild relatives (Burke and Rieseberg 2003; Snow et al. 2003).
Herbivore pressure is obviously a factor affecting the fitness of weeds and wild plants.
Insect-resistant h ybrids m ay h ave en hanced f itness v alues i n co mparison to th eir w ild
relatives (Vacher et al. 2004; Moon et al. 2007; Letourneau and Hagen, 2009). Because of this
higher fitness, resistant plants are expected to increase in populations where gene flow occurs.
The rate of the frequency change would depend on the advantage provided by the transgene,
but also on the growth conditions in the habitat, in particular intra-population competition. For
example, plant density has recently been considered as an ecological factor interacting with
fitness ( Weis an d H ochberg 2000; V acher e t al. 2004) . M ore c omplex e nvironments m ight
increase the relative fitness of transgenic hybrids and backcross generations. However, we are
not yet c lear on how he rbivore a nd c ompetition pr essure t ogether a ffect t he f itness
performance of insect-resistant hybrids and wild relatives.
In th is s tudy, w e r eport o n a p reliminary experiment to s imulate th e imp acts o f
herbivore p ressure o n t he f itness o f s tabilized h ybrid p rogeny b etween t ransgenic Brassica
napus and wild B. juncea under different competition intensities. B. juncea is known to b e
able to be fertilized by pollen of B. napus (Roy 1978; Frello et al. 1995) such that interspecific
hybrids are likely to occur, which may in turn transfer the transgenic insect-resistance to the
wild B. juncea populations through backcrossing. Indeed, the absence of fitness cost of the
transgene m ight a llow t he t ransgene t o pe rsist i n t he f ield popul ations ( Di e t al., 2009) .
However, t he s peed a t which t he t ransgene would s pread t hrough t he wild popul ation i s
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