Environmental and landscape effects on cross‐pollination rates observed at long distance among French oilseed rape Brassica napus commercial fields

Abstract

Summary 1.Evaluation of our ability to predict cross-pollination rates (CPR) at long distance using dispersal functions estimated in experimental set-ups differing by either their scale or their environmental conditions is crucial to establish appropriate management rules following the release of genetically modified (GM) crops. 2. From 1998 to 2004 we measured oilseed rape CPR in commercial fields for 44 donor-recipient couples separated by 220 up to 2000 m, from up to three different pollen donor cultivars in two French oilseed rape production areas. We followed the same sampling and screening designs and tested the effect of region, year, size, cultivar and distance on the observed CPR. 3. We then compared observed CPR to predictions from six empirical pollen dispersal models based on dispersal kernels that were fitted previously at the local and landscape scales. These predictions allowed us to test the possibility to extrapolate and up-scale dispersal kernels. 4. The observed CPR varied from 0% to 0·092%. They were higher in Champagne-Ardennes, where they depended negatively on distance, than in Bourgogne where they did not depend on distance. CPR also differed among years, being nil for the last 3 successive years, partly because of different environmental conditions and detection issues. CPR depended further on the source cultivars due to differences in pollen production. Dispersal kernels fitted at the local scale lead to systematic and huge underestimation of CPR, when observed. The power-law kernel fitted at the landscape scale under-estimated CPR by two orders of magnitude above 400 m but followed the rate of decrease of the observed pollination with distance. 5. Synthesis and applications . Caution should be taken when extrapolating and up-scaling dispersal kernels and models because predictions may differ greatly from observations. Models should rely at least upon dispersal kernels estimated from landscape-scale data obtained in different regions. Models should also integrate several phenomena at the agro-ecosystem scale including the dispersal by insects and become more mechanistic to account for variations observed among years, environments and distance to borders.

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).…”