Hybridization and backcrossing between transgenic oilseed rape and two related weed species under field conditions

Abstract

Determining the frequency of crop-wild transgene flow under field conditions is a necessity for the development of regulatory strategies to manage transgenic hybrids. Gene flow of green fluorescent protein (GFP) and Bacillus thuringiensis (Bt) transgenes was quantified in three field experiments using eleven independent transformed Brassica napus L. lines and the wild relatives, B. rapa L. and Raphanus raphanistrum L. Under a high crop to wild relative ratio (600:1), hybridization frequency with B. rapa differed among the individual transformed B. napus lines (ranging from ca. 4% to 22%), however, this difference could be caused by the insertion events or other factors, e.g., differences in the hybridization frequencies among the B. rapa plants. The average hybridization frequency over all transformed lines was close to 10%. No hybridization with R. raphanistrum was detected. Under a lower crop to wild relative ratio (180:1), hybridization frequency with B. rapa was consistent among the transformed B. napus lines at ca. 2%. Interspecific hybridization was higher when B. rapa occurred within the B. napus plot (ca. 37.2%) compared with plot margins (ca. 5.2%). No significant differences were detected among marginal plants grown at 1, 2, and 3 m from the field plot. Transgene backcrossing frequency between B. rapa and transgenic hybrids was determined in two field experiments in which the wild relative to transgenic hybrid ratio was 5-15 plants of B. rapa to 1 transgenic hybrid. As expected, ca. 50% of the seeds produced were transgenic backcrosses when the transgenic hybrid plants served as the maternal parent. When B. rapa plants served as the maternal parent, transgene backcrossing frequencies were 0.088% and 0.060%. Results show that transgene flow from many independent transformed lines of B. napus to B. rapa can occur under a range of field conditions, and that transgenic hybrids have a high potential to produce transgenic seeds in backcrosses.

Genetic structure and relationships within and between cultivated and wild sorghum (Sorghum bicolor (L.) Moench) in Kenya as revealed by microsatellite markers

“…verticiliflorum being well documented within and around cultivation in Africa (Dogget and Majisu 1968;Dogget and Prasada Rao 1995;Tesso et al 2008). In a study related to the present one, Mutegi et al hybridisation as has demonstrated between GM oilseed rape (Brassica napus L.) and its wild relatives (Halfhill et al 2004). …”

The biology of Canadian weeds. 132. Raphanus raphanistrum L.

“…In Australia (Rieger et al 2001), no hybrids were detected when R. raphanistrum served as the female parent in experimental field plots of imidazolinoneresistant B. napus, and only two hybrids (both fertile amphidiploids AACCRrRr, 2n = 56) when R. raphanistrum served as the pollen donor (hybridization frequency of <4 × 10 -8 ). In contrast, no hybrids were detected in Swiss (Thalmann et al 2001) and US (Halfhill et al 2004) field studies. Polymorphism for interspecific hybridization ability was detected among individuals of wild radish in France (Guéritaine and Darmency 2001), as well as among canola cultivars (Baranger et al 1995;Guéritaine et al 2003b).…”

Quantifying the introgressive hybridisation propensity between transgenic oilseed rape and its wild/weedy relatives

“…Within B. napus fields, hybridisation frequencies range from 0 to 69% of the seeds harvested on B. rapa plants depending on the ratio of parental species, parental genotypes, synchrony in flowering times, chromosome location of the (trans)gene, spatial distribution of species, environment and agricultural practices (Jørgensen and Andersen 1994;Jørgensen et al 1996;Landbo et al 1996;Mikkelsen et al 1996b;Warwick et al 2003;Halfhill et al 2004;Norris et al 2004;Leflon et al 2006;Simard et al 2006). Although B. rapa is suggested to be widespread at low levels of infestation in oilseed rape fields in the UK, Wilkinson et al (2003a) estimated that -for a mean of 876,000 weedy B. rapa plants -17,000 hybrids would be formed annually in agricultural habitats.…”