Costs of transgenic herbicide resistance introgressed from Brassica napus into weedy B. rapa

Abstract

Wild relatives of genetically engineered crops can acquire transgenic traits such as herbicide resistance via spontaneous crop–wild hybridization. In agricultural weeds, resistance to herbicides is often a beneficial trait, but little is known about possible costs that could affect the persistence of this trait when herbicides are not used. We tested for costs associated with transgenic resistance to glufosinate when introgressed into weedy Brassica rapa. Crosses were made between transgenic B. napus and wild B. rapa from Denmark. F1 progeny were backcrossed to B. rapa and BC1 plants were selected for chromosome numbers similar to B. rapa. Further backcrossing resulted in a BC2 generation that was hemizygous for herbicide resistance. We quantified the reproductive success of 457 BC3 progeny representing six full‐sib families raised in growth rooms (plants were pollinated by captive bumblebees). Pollen fertility and seed production of BC3 plants were as great as those of B. rapa raised in the same growth rooms. Segregation for herbicide resistance in BC3 plants was 1:1 overall, but the frequency of resistant progeny was lower than expected in one family and higher than expected in another. There were no significant differences between transgenic and nontransgenic plants in survival or the number of seeds per plant, indicating that costs associated with the transgene are probably negligible. Results from this growth‐chamber study suggest that transgenic resistance to glufosinate is capable of introgressing into populations of B. rapa and persisting, even in the absence of selection due to herbicide application.

From Microphysics to Mesophysics: Obtaining Effective Properties from Microscopic Behaviors

“…Genes inserted by recombinant DNA technology and selected for plant breeding programmes demonstrate Mendelian segregation and recombination and 'flow' from plant to plant exactly as resident genes. Experiments in which crosses have been made between transgenic crops and wild relatives show segregation patterns consistent with the expectation that transgenes are inherited in the same way as naturally occurring genes (Snow et al 1999, Halfhill et al 2002in these examples for herbicide tolerance and Bt in Brassica and Bt in sunflowers). Evidence that past gene flow has had an impact on the population biology and survival of wild species in the UK is difficult to find, although the potential impact globally of modern crops on local land races of several species is a widely acknowledged problem and the presence of genes derived from crops has been established in a number of wild species (e.g.…”

Monitoring the escape of transgenic oilseed rape around Japanese ports and roadsides

“…The fitness of the resulting hybrids or backcrossed plants is typically reduced in early generations; the F 1 and BC 1 generations usually exhibit reduced pollen fertility and seed production (Brown and Brown, 1996;Frello et al, 1995;Mikkelsen et al, 1996b). However, Snow et al (1999) found that the magnitude of the fitness disadvantages in hybrid progeny of the cross between B. rapa and B. napus diminished with successive generations of backcrossing. They also showed that the benefits or costs associated with the transgenic glufosinate resistance were negligible in the absence of selection caused by herbicide application.…”

Male fitness of oilseed rape (Brassica napus), weedy B. rapa and their F1 hybrids when pollinating B. rapa seeds

“…Hybrids were thus hemizygotic for the bargene giving tolerance to the herbicide glufosinate. The parents and production of their hybrids are described in Snow et al (1999).…”

“…Among the backcross offspring, sired by hemizygous transgenic F 1 parents, half are expected to carry the bar gene and thus be tolerant to glyphosinate (references in Snow et al, 1999). To evaluate tolerance, 5 × 5 mm filter papers wetted with a 0.2% glufosinate solution (Basta) were placed on a leaf of each plant (when ෂ5 leaves were present).…”