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competition diminished the difference between the hybrid progeny and wild plants, although
hybrids produced lower fitness than wild radish under no competition conditions. Alternately,
one c ould i magine t hat DM pl ants a lso di splayed s ome i ntrogressed c rop ge nes, e .g. t he
intense yellow f lower c olor, a nd t hese genes c ould he lp t hem t o ove rcome t he c ompetition
from t he c rop e asier t han non -introgressed pl ants. W ith a rtificial p opulations o f w ild and
hybrid r adishes i n a rable fields i n U SA, C ampbell e t a l. ( 2006) f ound that introgressed
hybrids showed greater survival and fitness after four generations of introgression than wild
plants i n a ne w ha bitat. Introgression vi a h ybridization m ay l ead t o adaptive e volution
(Ellstrand a nd S chierenbeck 2000) , be cause i ntrogression m ay generate nove l a daptations
enhancing the fitness of weedy hybrid lineages in certain environments (Rieseberg et al. 1999;
Lexer et al. 2003).
Conclusion
Our r esults s howed t hat t he m orphological traits discriminated th e wild radish populations.
Synthetic ch aracteristics o f t he m ultivariate an alyses showed B T a nd N M popul ations
different from BG and DM, although NM w as often intermediate. The geographic distance
was the shortest between BT and NM, which could explain that they showed less difference
between t hem t han w ith t he i nland B G or f arthest D M popul ations. H owever, t he di stance
cannot a ccount f or t he grouping of BG and D M. W hen a nalyzing s pecific ch aracteristics
separately, some arguments were equally in favor of the interaction between introgression and
natural selection or distance-mediated divergence on m orphology traits, as observed in other
cases (Lenormand 2002; Postma and van Noordwijk 2005). However, the long exposition of
the N M popul ations t o pollen of oi lseed rape, for a t l east 200 years, had no a pparent or
discriminant effect on the morphology, growth and reproduction of the wild radish plants in
that r egion. A part, pe rhaps, t he hi gher pol ymorphism, t here i s no evidence o f a dr amatic
evolution of t he popul ations of t hat r egion w ith regard t o t he va riability found i n t he t hree
other regions. Molecular evidence of ancient introgression is necessary to confirm that some
population would have been introgressed, and this is difficult because both B. napus and R.
raphanistrum share a large part of their genetic background within the Brassica tribe. In case
introgression were detected, future study should focuses on the benefit and cost associated to
these genes and their role for field adaptation compared to the potential role of the transgenes
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