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Gene flow in the environment - genetic pollution?
... Le canola transgénique tolérant aux herbicides représente, à cet égard, un cas bien documenté. Proche parente d'espèces sauvages colonisant les zones cultivées (Chèvre et al. 2000), cette plante produit une quantité abondante de pollen capable de se déplacer sur des distances importantes par l'action du vent et des insectes pollinisateurs (Lavigne et al. 1998; Rieger et al. 2002; Squire et al. 2000). Ce mouvement du pollen, couplé à une dispersion des graines dans les champs au moment de la récolte et des premières étapes de manutention des graines (Gulden et al. 2003), crée un contexte favorable aux phénomènes d'hybridation dans les champs d'origine, les champs voisins et les zones proximales non cultivées (Chèvre et al. 1997; Lefol et al. 1996). ...
... Ce mouvement du pollen, couplé à une dispersion des graines dans les champs au moment de la récolte et des premières étapes de manutention des graines (Gulden et al. 2003), crée un contexte favorable aux phénomènes d'hybridation dans les champs d'origine, les champs voisins et les zones proximales non cultivées (Chèvre et al. 1997; Lefol et al. 1996). Plusieurs études ont rapporté, par exemple, la présence d'un transgène de tolérance aux herbicides dans le génome d'espèces proches du canola (Chèvre et al. 2000; Jorgensen et Andersen 1994; Mikkelsen et al. 1996; Pinder et al. 1999; Simpson et al. 1999; Squire et al. 2000; Warwick et al. 2003). Comme le processus d'hybridation, l'établissement et la propagation d'individus hybrides dans l'environnement sont toutefois soumis à des contraintes variées incluant le mode de propagation de l'hybride considéré, la fertilité du pollen et des ovules qu'il produit, son efficacité à produire des descendants, la viabilité et le nombre de ses graines ainsi que son efficacité à se propager en présence d'organismes compétiteurs, prédateurs ou pathogènes (Conner et al. 2003). ...
The large-scale adoption of transgenic crops over the last ten years has led several groups to question the possible impacts of these new plant lines on agricultural and natural ecosystems. In particular, questions have been raised about the impact of the transgenes on the environment, and about an eventual "pollution" of the overall genetic pool of living organisms at the ecosystem level. After an introduction on the possible environmental impacts of transgenic plants, this review summarizes the current knowledge on the fate - or migration - of transgenes in the environment. Hybridization and introgression processes involving transgenic crops and their close relatives are first considered. Transgene integration in non-related organisms by horizontal gene transfer is then considered. A companion review in this same issue addresses the environmental impacts of recombinant proteins encoded by the transgenes (Michaud 2005).
... Le canola transgénique tolérant aux herbicides représente, à cet égard, un cas bien documenté. Proche parente d'espèces sauvages colonisant les zones cultivées (Chèvre et al. 2000), cette plante produit une quantité abondante de pollen capable de se déplacer sur des distances importantes par l'action du vent et des insectes pollinisateurs (Lavigne et al. 1998;Rieger et al. 2002;Squire et al. 2000). Ce mouvement du pollen, couplé à une dispersion des graines dans les champs au moment de la récolte et des premières étapes de manutention des graines (Gulden et al. 2003), crée un contexte favorable aux phénomènes d'hybridation dans les champs d'origine, les champs voisins et les zones proximales non cultivées (Chèvre et al. 1997;Lefol et al. 1996). ...
... Plusieurs études ont rapporté, par exemple, la présence d'un transgène de tolérance aux herbicides dans le génome d'espèces proches du canola (Chèvre et al. 2000;Jorgensen et Andersen 1994;Mikkelsen et al. 1996;Pinder et al. 1999;Simpson et al. 1999;Squire et al. 2000;Warwick et al. 2003). En bref, ces travaux démontraient que des hybridations interspécifiques surviennent à des taux mesurables en milieu agricole entre le canola et des espèces proches comme la moutarde des oiseaux (Brassica rapa L.) ou la moutarde indienne (B. ...
L’adoption à grande échelle des cultures transgéniques depuis dix ans a soulevé de nombreuses questions quant aux impacts possibles de ces nouvelles lignées végétales sur les écosystèmes agricoles et naturels. Des questions ont été soulevées, en particulier, sur le devenir des transgènes dans le milieu et sur une possible « pollution » du patrimoine génétique des organismes vivants à l’échelle des écosystèmes. Après une énumération des impacts environnementaux associés aux végétaux transgéniques, cet article de synthèse dresse un aperçu des connaissances actuelles sur le devenir – ou la migration – des transgènes dans le milieu. Les phénomènes d’hybridation et d’introgression génique en direction d’espèces ou de lignées apparentées sont d’abord abordés, après quoi sont considérés les phénomènes de transfert horizontal des transgènes en direction d’organismes non apparentés. Un article complémentaire publié dans ce même numéro traite de l’impact environnemental des protéines recombinantes encodées par les transgènes (Michaud 2005).
... (13) These large-scale field observations, typically combining a variety of scientific disciplines with painstaking observation (including many hours dedicated to counting pollen grains), brought insect-mediated gene flow to the fore thanks to their ability to pay attention to minor actors and occurrences. (14) In the words of a research team, ``the crux [of the landscape-scale studies] is detecting and interpreting rare events and small numbers'' (Squire et al, 2000, page 46). By lowering the threshold of observability while extending the area under investigation, these analyses not only raised the estimates of gene flow, both in terms of its quantity and the spatial distance over which it occurs, but were also able to take into consideration , even if only in a tentative fashion, the flying ranges of bees and other pollinating insects. ...
Over the last decade the flying patterns and foraging behavior of bees have become a matter of public policy in the European Union. Determined to establish a system where transgenic crops can ‘coexist’ with conventional and organic farming, the EU has begun to erect a system of demarcations and separations designed to minimize the extent of ‘gene flow’ from genetically modified plants. As the European landscape is regimented through the introduction of isolation distances and buffer zones, bees and other pollinating insects have become vectors of ‘genetic pollution’, disrupting the project of cohabitation and purification devised by European authorities. Drawing on the work of Michel Serres on parasitism, this paper traces the emergence of bees as an object of regulatory scrutiny and as an interruptor of the ‘coexistence’ project. Along with bees, however, another uninvited guest arrived unexpectedly on the scene: the beekeeper, who came to see his traditional relationship to bees, crops, and consumers at risk. The figure of the parasite connects the two essential dynamics described in this paper: an escalation of research and the intensification of political attributes.
The present paper reports on three sets of experiments exploring the persistence of seeds of oilseed rape (Brassica
napus). The first, where known numbers of seeds were buried in September 1991 in two field experiments, demonstrated substantial initial losses of seeds, such that only 0·2 and 3·8% of seeds were still present after 4 months. In these experiments, which were not disturbed by mechanical cultivation, there was little evidence of further decline over the following 13 months. In the second of the two experiments, seeds were then left undisturbed for a further 136 months. A mean of 1·8% of seeds were still present after this period, providing further confirmation of the lack of decline in seed numbers in these undisturbed conditions. In the second pair of experiments, known numbers of seeds of three rape cultivars were broadcast onto plots and then either ploughed into the soil immediately after the start of the experiments, or were exposed to weekly shallow tine cultivation followed by ploughing after 4 weeks. The former created a larger seedbank than the latter. The experiments were then ploughed, annually (Expt 1) or at less frequent intervals (Expt 2); appreciable numbers of seeds survived for 65 months in both. Calculations based on exponential decline curves indicated that 95% seed loss would take 15–39 months, depending on the site, cultivar and initial post-harvest stubble treatment. The third part of the paper is based on more detailed studies of persistence of seeds of six cultivars in Petri dishes and buried in 25 cm pots. This work confirmed that cultivars differed in their persistence, as Apex was confirmed as highly persistent, whereas Rebel was short-lived. There were inconsistencies in the response of cultivar Synergy between the Petri-dish and pot experiment, which need further study. This experiment also reinforced the conclusion of the initial field experiments that little seed loss occurs in the absence of cultivations. Appreciable numbers of rape seeds will persist up to 4 years, in normal cropping conditions and in the absence of cultivation one experiment has confirmed persistence for over 11 years.
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