The studies on gene flow from GM herbicide-tolerant rapeseed to cruciferous weeds
2005; Elsevier BV; Linguagem: Inglês
ISSN
1000-0933
Autores Tópico(s)Transgenic Plants and Applications
ResumoEight common Chinese cruciferous weeds were grown in pairs with the glyphosate-tolerant GM rapeseed variety Q3. The frequency of gene flow from the herbicide-tolerant GM rapeseed to these cruciferous weeds was studied under either natural or manual pollination conditions. This study is to provide scientific evidence for the evaluation of the ecological safety of growing herbicide-tolerant GM rapeseed. Firstly, we studied the gene flow from glyphosate-tolerant GM rapeseed to cruciferous weeds under natural pollination conditions. Eight cruciferous weed species including Capsella bursa-pastoris, Crdamine hirsuta, Descurainia sophia, Orychophragmus violaceus, Rorippa palustris, Thlaspi arvense, Rorippa montana and B.juncea were grown in pairs with glyphosate-tolerant GM rapeseed variety Q3. The row ratio was 3∶3. The seeds of the selected eight weeds were sown three times, each with a 20-days gap. The first time was 20 days earlier, the second period was at the same time and the third period was 20 days late when compared to the sowing date of rapeseed. This is to ensure that at least some plants from each weed species could be at the synchronized flowering period with rapeseed. The planting area of each pair is 30m~2. All plants were allowed to pollinate naturally. Each weed species was harvested separately after maturity. The screening of glyphosate-tolerant weeds contaminated by the pollen drift of GM rapeseed was carried out in field conditions in the following autumn. Seeds were pretreated with GA_3 to break dormancy. Seedlings at 3~4 leaves stage were spread with 0.15% glyphosate at a rate of 450 kg/hm~2. The survival rate of spread weeds were investigated 15 days after the spread and the rate of gene flow through pollen drift from rapeseed were calculated. The results demonstrated that under natural pollination conditions, there was no gene flow from glyphosate-tolerant GM rapeseed to seven out of the eight weed species examined. These weeds are Capsella bursa-pastoris, Crdamine hirsuta, Descurainia sophia, Orychophragmus violaceus, Rorippa palustris, Thlaspi arvense and Rorippa montana. The total sample size of these seven weeds was 240,000 plants none of which survived the herbicide spread. In contrast, 205 out of 23,157 B. juncea plants examined survived the herbicide spread, and it's the rate of the gene flow through pollen drift was estimated as 0.885%. Secondly, we have also studied the gene flow from glyphosate-tolerant GM rapeseed to cruciferous weeds with the assistance of manual pollination in addition to natural pollination. The seven cruciferous weed species were grown in pots, about 10~20 plants in each pot. The weeds-growing pots were surrounded by glyphosate-tolerant GM rapeseed Q3 plants which were sown in three time periods each with a 15-days gap to ensure the synchronized flowering between the rapeseed plants and each of the weed species. During the whole flowering season, in addition to natural pollination, manual pollination of each of flowering weed plants using rapeseed pollen was carried out between 9 am to 4 pm daily. The harvested mature weed seeds were screened for glyphosate-tolerance in the following autumn. Seedswere pretreated with GA_3 and germinated in Petri dishes prior to sowing to the field. Weed seedlings at 3-4 leaves stage were spread with 0.15% glyphosate herbicide at 450 kg/hm~2. None of the 5234 weed plants survived the glyphosate spread, indicating that gene flow by pollen drift from glyphosate-tolerant rapeseed to the seven cruciferous weeds examined did not occur, even with the assistance of manual pollination. This is perhaps because of the high level of sexual incompatibility between rapeseed and each of the seven weed species examined. This clearly demonstrated the biosafety of growing GM rapeseed in relation to the seven cruciferous weeds examined in this study. However, there is a relatively high level of sexual compatibility between rapeseed and the wild B. juncea and subsequently the rate of gene flow through pollen drift reached as high as 0.885% in the cur
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