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

more easily sieved out by harvesters and fall onto the soil, and further buried in the seed
bank of soil. In addition, the small seed dispersed more easily through wind and animals,
such that the survival of small-sized seeds of weeds could be higher in conventional tillage
systems and arable habitats. These seeds could be volunteers in the subsequent years, and
they might represent the main risk of transgene escape in the field. Hence, the small size in
hybrids might not be a counterbalancing force exposing them to higher competition from
the neighborhood but be possible resources for further gene flow (Chapter 2.2).
We did not study the successive generations of these plants with different seed size
in fields. Backcross progeny with pollens of oilseed rape (Brassica napus) is more easily
formed and produces more seeds than that with pollens of mustard (B. juncea). Hence, the
progeny that has traits of oilseed rape will be produced in or outside of arable fields. Most of
plants backcrossed with oilseed rape pollen had crop-like traits, for example larger flower
that permit pollinators more easily to access and produced more seeds. Their seeds were
larger and germinated better than the seeds produced with B. juncea pollen, suggesting they
show a similar survive dynamic and emergence with oilseed rape. In our experiment with
herbicide resistance, their chromosome number followed a Normal distribution, and the
herbicide-resistance gene was consistent with Mendelian ratio. However, this is not
automatic, and it depends on the insertion loci of transgene on A or C genome and on the
backcrossing with A or B genome in mustard (Frello et al. 1996). This transgene could also be
resistant to insects or others that permit them continue survive in fields. Pollen flow to
susceptible plants within the mixed stand was occurred. These results suggest that the
resistant BC1 produced with B. napus pollen could frequently occur and easily establish as a
false feral crop population within cultivated fields and along roadsides. The establishment of
crop-like progeny is much more rapid and hosts a large genetic variability compared to crops,
which could be the source of further rapid adaptation and evolution (Chapter 2.3).
Does the hybridization effects on morphology will exist after long term introgression
of crop gene in wild relatives, even without transgene conferring new traits? We first
propose the hypothesis that gene flow increases with the increasing coexistence between
two species, oilseed rape and wild radish (Raphanus raphanistrum). The putative ancient
introgressed populations showed polymorphism and intermediate characteristics in silique
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