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

more flowers and larger plant size than the lines with small flowers. Therefore, if white color
petal allele is lost during the process of introgression when pollinators are selecting for yellow
petals, l arger f lower an d l arger pl ant w ill be i nfrequent i n a popul ation. B ased on t his, i f
transgenes related with white petal are transferred from the crop to the wild plant, the risk of
transgene in trogression is lo w in f ields w here p ollinators s elect f or yellow p etals, a nd
inversely, it is high.
Thus, in turn, introgression of transgenes from crops to wild r elatives also could be
influenced by morphological traits. Seed size is another example. Gene flow and introgression
might be hampered by small seed size of hybrids between crops and wild relatives (Wei and
Darmency 2008) because certain studies indicated that interspecific hybrids are present only
among seeds with a diameter less than 1.6 m m (eg. Eber et al. 1994; Baranger et al. 1995;
Chèvre e t a l. 2000) . For e xample, m ost crosses b etween o ilseed r ape ( Brassica napus ) a nd
wild r elatives o nly p roduced s mall s eeds, s uch as B. j uncea (Bing et a l., 1996) , B. r apa
(Jørgensen and Andersen, 1994), Hirschfeldia incana and R. raphanistrum (Eber et al., 1994;
Chadoeuf et al., 1998). Wei and Darmency (2008) employed male sterile B. napus and five
wild relatives to obtain hybrids and found all seeds of four hybrids were small. Small seeds
perform d isadvantage b ecause s eed m ass affects t he em ergence and i nitial s eedling s ize
(Aparicio et al. 2002; Westoby et al., 2002). This could decrease the plant fitness of smallseeded
pl ants ( Gardner and va nderlip 1989; V erdu a nd T raveset, 2005) , e specially und er
particular hazard conditions (such as high density, shade, drought or herbivory).
1.5.2 Consequences of interspecific introgression on population dynamics
Gene f low a nd i ntrogression pl ays a c rucial r ole i n t he e volution of natural popul ation
(Postma a nd N oordwijk 2005; Lenormand 2002 ), be cause gene f low c ould c ounteract t he
negative effects of genetic drift, inbreeding (Ebert et al. 2002), genetic differentiation (Postma
and Noordwijk 2005), and local selection (Lenormand 2002), on genetic variation and thus on
the evolution of local adaptations. Over short time-scales, invading h ybrid populations may
experience s trong s election ( Sakai e t a l., 20 01; A llendorf & Lundquist, 2003) . T he
evolutionary t rajectory of w eed popul ations m ay persistently be a ltered b y t he l ong-term
introgression of c rop alleles into weed populations, such as with sunflower (Whitton et al.,
1997), oi lseed r ape ( Hansen e t a l., 2001) and r adish ( Snow e t al., 200 1). T he i nteraction
28