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oilseed rape and B. oleracea is very low, hybridization could be achieved by hand pollination.
In t he U nited K ingdom, s pontaneous h ybrids be tween B. napus and B. o leracea were
observed i n t he B. oleracea wild popul ation, us ing f low c ytometry a nd c rop-specific
microsatellite markers (Ford et al. 2006). No natural crosses are reported between the three
species an d B. ni gra (Bing et a l. 1996 a), but male s terile B. napus produce s pontaneous
hybrids w hen pl aced i n a B. ni gra stand ( Wei and D armency 2008) , although t here i s no
indication a bout t he r eciprocal c ross. Hybrids f ormed be tween B. r apa and B. ni gra was
obtained by ovule culture (Bing et al. 1996b). Hybridization of B. napus× B. carinata and B.
juncea × B. carinata have been a chieved b y ha nd pollination (Chang et al. 2007). H ybrids
between B. rapa and B. carinata were only obtained when B. carinata was used as the female
parent (Choudhary et al. 2000).
No natural crosses occurred between the three species and Sinapis arvensis (Bing et al.
1996a, Lefol et al. 1996), indicating that direct transgene escape from B. napus to S. arvensis
appears very unlikely (Moyes et al. 2002).Spontaneous hybridization between B. napus and
wild radish (Raphanus raphanistrum, Rr, 2n=18) could occur in the nature, and some hybrids
were reported on male sterile B. napus as mother in Canada and Denmark (Eber et al. 1994;
Baranger et a l. 1995; A mmitzboll a nd J orgensen 2006) a nd a t l ow f requency on R .
raphanistrum as mother in Australia and France (Darmency et al. 1998; Chèvre et al. , 2000;
Rieger et al. 2001 ). The frequency of hybridization depended on environmental conditions,
oilseed rape variety, wild radish populations and their density (Eber et al. 1994; Baranger et al.
1995; Darmency et al. 1998; Chèvre et al. 1996, 2000; Rieger et al. 2001; Ammitzboll and
Jorgensen 2006). Genetic polymorphism for pollen germination and ovule fertilisation also
represented va riation of pr e-zygotic b arriers to in terspecific h ybridisation ( Guéritaine a nd
Darmency 2001).
Several ove rviews on h ybridization be tween B. napus and its w ild r elatives a nd
associated species are available in Rieger et al. (1999), FitzJohn et al. (2007), Andersson and
de Vicente (2010).
1.2 Dispersal of transgenes
Extensive transgene flow between oilseed rape varieties has been detected in Canada resulting
in the generation of volunteers that contain three types of herbicide resistance (Hall et al. 2000;
Beckie et al. 2003; Knispel et al. 2008). The flow of transgenes could have occurred within a
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