Modelling and estimating pollen movement in oilseed rape (Brassica napus) at the landscape scale using genetic markers

Abstract

Understanding patterns of pollen movement at the landscape scale is important for establishing management rules following the release of genetically modified (GM) crops. We use here a mating model adapted to cultivated species to estimate dispersal kernels from the genotypes of the progenies of male-sterile plants positioned at different sampling sites within a 10 x 10-km oilseed rape production area. Half of the pollen clouds sampled by the male-sterile plants originated from uncharacterized pollen sources that could consist of both large volunteer and feral populations, and fields within and outside the study area. The geometric dispersal kernel was the most appropriate to predict pollen movement in the study area. It predicted a much larger proportion of long-distance pollination than previously fitted dispersal kernels. This best-fitting mating model underestimated the level of differentiation among pollen clouds but could predict its spatial structure. The estimation method was validated on simulated genotypic data, and proved to provide good estimates of both the shape of the dispersal kernel and the rate and composition of pollen issued from uncharacterized pollen sources. The best dispersal kernel fitted here, the geometric kernel, should now be integrated into models that aim at predicting gene flow at the landscape level, in particular between GM and non-GM crops.

Scientific Opinion on a request from the European Commission related to the prolongation of prohibition of the placing on the market of genetically modified oilseed rape event GT73 for import, processing and feed uses in Austria

“…Since feral plants derived from cultivation (as distinct from import) occur at too low a frequency to affect the tolerance threshold of 0.9% in the EU, even if they were assumed all to be transgenic, several authors concluded that feral GMHT plants resulting from seed import spills will have little relevance as a potential source of pollen or seed for GM admixture in conventional oilseed rape crops (Messéan et al, 2009;Squire et al, 2011;Devos et al, 2012 (Colbach et al, 2001a(Colbach et al, ,b, 2005Devaux et al, 2005Devaux et al, , 2007Devaux et al, , 2008Gruber and Claupein, 2006;Knispel et al, 2008;Colbach, 2009)" (EFSA, 2009b.…”

“…Using male-sterile plants (which produce no pollen of their own) as recipients tends to overestimate the actual frequency of cross-fertilisation that would occur between the crop plants and pollen-fertile ferals by more than 10-fold (Ramsay et al, 2003; GR Squire, unpublished data), but demonstrates the potential for its occurrence. This approach combined with modelling work confirmed that cross-fertilisation levels usually decline very steeply with distance from one field to an adjacent or nearby field Beckie and Hall, 2008), but they occur at low frequency over several kilometres (Rieger et al, 2002;Ramsay et al, 2003;Devaux et al, 2005Devaux et al, , 2007Devaux et al, , 2008Chifflet et al, 2011). It is expected that crossing of the order of 1 to 10% will occur to feral plants a few metres from a donor, and of 0.1 to 0.01% to ferals that are 100 m away (SIGMEA, 2010).…”

“…Few direct measurements to quantify crossings between commercially grown oilseed rape and feral plants have been made so far, but the fact that crossing occurs, and hence genomes of old and new varieties combine, was demonstrated at several localities in the EU (Charters et al, 1999;Bond et al, 2004;Dietz-Pfeilstetter et al, 2006Pascher et al, 2006Pascher et al, , 2010Elling et al, 2009). More generally, the potential for cross-fertilisation of feral plants by the crop plant simultaneously in flower over a range of distances has been demonstrated by the use of small groups of male-sterile recipient plants distributed in the landscape (Ramsay et al, 2003;Devaux et al, 2005Devaux et al, , 2007Devaux et al, , 2008Chifflet et al, 2011). Using male-sterile plants (which produce no pollen of their own) as recipients tends to overestimate the actual frequency of cross-fertilisation that would occur between the crop plants and pollen-fertile ferals by more than 10-fold (Ramsay et al, 2003; GR Squire, unpublished data), but demonstrates the potential for its occurrence.…”

Scientific Opinion on a request from the European Commission related to the prolongation of prohibition of the placing on the market of genetically modified oilseed rape events Ms8, Rf3 and Ms8 × Rf3 for import, processing and feed uses in Austria

“…Few direct measurements to quantify crossings between commercially grown oilseed rape and feral plants have been made so far, but the fact that crossing occurs, and hence genomes of old and new varieties combine, was demonstrated at several localities in the EU (Charters et al, 1999;Bond et al, 2004;Dietz-Pfeilstetter et al, 2006Pascher et al, 2006Pascher et al, , 2010Elling et al, 2009). More generally, the potential for cross-fertilisation of feral plants by the crop plant simultaneously in flower over a range of distances has been demonstrated by the use of small groups of male-sterile recipient plants distributed in the landscape (Ramsay et al, 2003;Devaux et al, 2005Devaux et al, , 2007Devaux et al, , 2008Chifflet et al, 2011). Using male-sterile plants (which produce no pollen of their own) as recipients tends to overestimate the actual frequency of cross-fertilisation that would occur between the crop plants and pollen-fertile ferals by more than 10-fold (Ramsay et al, 2003;GR Squire, unpublished data), but demonstrates the potential for its occurrence.…”

CMS Lines for Evaluation of Pollen Flow in Sunflower Relevance for Transgene flow Mitigation

“…During the last two decades a number of studies were devoted to the assessment and modeling of pollen flow in different crops in order to evaluate the possibility for coexistence between transgenic and nontransgenic plants (sunflower (1); trees (6); maize (3); oilseed rape (4,5,23).…”