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

Introduction
In t he f ramework o f cu rrent r esearch o n t he r isk as sessment o f t he co mmercial r elease o f
genetically modified (GM) crops, one of main concerns is whether transgenes could persist in
the agro-ecosystem [1]. In the case of oilseed rape (Brassica napus), transgenes could escape
through volunteers plants descended from seeds shattered before or spilled during harvest on
previous years and that can survive for years into the soil seed bank [2] and affect both the
habitat [ 3] a nd t he qua lity o f c rop h arvest [ 4]. T hey could a lso e scape vi a s pontaneous
hybridization w ith a nd i ntrogression t o w ild r elatives [ 5, 6] . V olunteers a nd h ybrids w ere
observed in the agro-ecosystem field together with sown crops and in their neighborhoods [7,
8].
The introgression between a genetically modified crop and a wild relative is generally
thought to p otentially modify th e genetic background of t he w ild s pecies, which t hus
generates either concerns about its weediness and competitiveness in the agro-ecosystem or
the risk of its extinction [6, 9, 10 ]. The backcrossing of hybrids with the crop parents could
also oc cur, w hich c ould r esult in th e introgression o f w ild c haracteristics in to f eral a nd
volunteer populations. This process is generally underestimated and little investigated because
the crop type is considered to be unfit to adapt to wild habitats [11]. However, the resulting
plants are thought to be too close to volunteers and to deserve separate studies.
Gene flow between B. napus and B. juncea has received less attention compared to the B.
napus / B . r apa case. B. j uncea, a wild r elative frequently f ound a s a w eed a nd a ruderal
component of roadsides and waste places in China, is a tetraploid species like B. napus and
preferentially s elf-pollinated w ith c onsiderable outcrossing rate. Hybrids a nd s ubsequent
backcross generations b etween B. napus and w ild B. j uncea were s uccessfully obt ained b y
open pol lination [ 12-14]. T he r elatively hi gh compatibility be tween B. napus and w ild B.
juncea raises t he bi osafety concern of t ransgene introgression. D i e t a l. [15] f ound t hat t he
hybrids formed be tween B. napus and w ild B. j uncea revealed m aternal effects, h igh
vegetative fitness and seed dormancy, which could increase the probability of the survival of
hybrids a fter t he oc currence of gene f low. H owever, W ei a nd D armency [ 16] s howed t hat
gene flow could be hampered by low seed size of hybrids because of the low emergence, low
survival r ate a nd d elayed f lowering due t o s maller s eeds. T herefore, i t i s not c lear unde r
which form the progeny of interspecific hybrids between these two species could survive and
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