| If herbicide-resistant(HR)transgenes escape from genetically modified herbicide-resistant(GMHR)crop to their weedy relatives through pollen flow,weeds with the HR trait might produce new problems for weed control.Wild B.juncea(AABB,2n=36)has become a major weed of cropping systems across western China,and extended eastward along the Yangtze River valley.The introgression of the herbicide-resistant gene from to wild B.juncea may cause much serious agricultural effects.However,the study on gene flow between(GMHR)oilseed rape(AACC,2n=38)and wild B.juncea focused only on fitness of F1 hybrids and BC1 and BC2.The researches on HR gene expression and fitness of successive generations are scant.On the basis of previous studies,the fifth and the sixth of-the first backcross generation(BC1F6,BC1F7),the fourth and the fifth of the second backcross generation(BC2F5,BC2F6),the third and fourth progeny of the third backcross generation(BC3F4,BC3F5)of transgenic glyphosate-resistant(DS-Roughrider,Roundup Ready,event RT73)and glufosinate-resistant oilseed rape(Swallow,Liberty Link,event HCN92)and wild B.juncea were researched on expression of herbicide-resistant gene.Furthermore,the fitness of BC1F6-7,BC2F5-6,BC3F4-5 with resistant gene in greenhouse and in field in different densities and planting proportions were researched.The long-term successive results will provide more scientific and deeper basis for safety assessment on gene flow from transgenic oilseed rape to wild B.juncea,The main results are as follow:1.Emergence rates and transgene expression of BC1F7,BC2F6,BC3F5 between glyphosate-or glufosinate-resistant transgenic oilseed rape and wild Brassica junceaThe emergence rates and glyphosate-or glufosinate-resistant transgene expression of BC1F7,BC2F6,BC3F5 between glyphosate-or glufosinate-resistant oilseed rape and wild B.juncea were studied.The results showed that the emergence rates of these backcross generations with either of resistant genes were between 91%and 94.11%.which were similar to that of wild B.juncea.The results implied that the emergence of these backcross generations did not showed weakness compared with that of wild B.juncea.After selectionby 1400 g(a.i.)ha-1 glyphosate or 700 g(a.i.)ha-1 glufosinate,the percentages of surviving plants in the backcross generations of glyphosate-resisitant transgenic rape and wild B.juncea are from 96.05%to 98.8%followed a normal Mendelian segregation,but the percentages of surviving plants in the backcross generations of glufosinate-resistant transgenic rape and wild B.juncea are from 54.85%to 82.47%,deviated from the expected Mendelian segregation.2.Fitness of the BC1F6-7R/L,BC2F5-6R/L,BC3F4-5R/L between herbicide-resistant transgenic oilseed rape and wild Brassica juncea in greenhouseIn order to evaluate potential introgression of transgene from transgenic glyphosate and glufosinate-resistant oilseed rape(Brassica napus)to wild B.juncea,composite fitness of BClmF6-7R/L and BClpF6-7R/L,BC2mF5-6R/L and BC2pF5-6R/L,BC3mF4-5R/L and BC3pF4-5R/L(R denotes glyphosate-resistant transgenic oilseed rape;L denotes glufosinate-resistant transgenic oilseed rape;m denotes backcross progeny obtained with wild B.juncea as maternal plants.p denotes backcross progeny obtained with wild B.juncea as paternal plants.)carring glyphosate-resistant gene or glufosinate-resistant gene in greenhouse were conducted by measuring the fitness components of vegetative variables including plant height,stem diameter,diameter of plant rosette,the first branch number/plant,above-ground dry biomass/plant,and reproductive variables including pollen viability,silique number,silique length and seed number/silique.The results denmostrated that,except for BClmF6R?BClpF6R and BC2pF5R,which had significant lower plant height,the other fitness components of BClmF6R?BClpF6R and BC2pF5R were similar to that of wild B.juncea.Te fitness components of BC3F4-5 were similar to that of wild B.juncea.The composite fitness of BC1F6-7R,BC2F5-6R and BC3F4-5R were similar to that of wild B.juncea.Except for BC1F6-7L and BC2F5-6L,BC1F6L?BC2F5L and BC3F4L,the former generations had significant lower plant height,the latter generations had significant lower stem diameter,the other fitness components of BC1F6-7L>BC2F5-6L and BC3F4-5L were similar to that of wild B.juncea.The composite fitness of BC1F6-7L,BC2F5-6L and BC3F4-5L were similar to that of wild B.juncea.The above results showed that BC1F6-7,BC2F5-6 and BC3F4-5 earring glyphosate-resistant gene or glufosinate-resistant gene had similar composite fitness to wild B.juncea in greenhouse.3.Fitness of BC1F6-7R/L,BC2F5-6R/L,BC3F4-5R/L between glyphosate-or glufosinate-resistant transgenic oilseed rape and wild Brassica juncea in fieldFitness of BClmF6-7R/L and BC1pF6-7R/L,BC2mF5-6R/L and BC2pF5-6R/L,BC3mF4-5R/L and BC3pF4-5R/L in field were studied in pure and mixed plots(wild B.juncea:backcross generation propotion=4:l9 3:2,1:1)at two densities(15 plants/plot and 30 plants/plot).The results showed that,in pure plots,the experimental backcross generations had similar composite fitness,except for BC1F6L and BC2F5L,which displayed significant lower fitness compared with wild B.juncea at high density.In mixed stands,at low density,compared with wild B.juncea,the composite fitness of BC1F6R and BC1F6L were significant lower at three propotions.BC2pF5R and BC2F5L displayed significant lower composite fitness at 4:1 and 3:2 propotions,and at three propotions,respectively.In mixed stands,at high density,the composite fitness of BC1F6R and BC2pF5R,BC1F6L,BC2F5L and BC3F4L were significant lower compared with wild B.juncea at three propotions.BC1F7L,BC2F6L and BC3F5L still were significant lower compared with wild B.juncea at 1:1propotions.In other cases,the composite fitness of backcross generations was as fit as wild B.juncea regardless of density and proportion.Therefore,the backeross generations carrying glyphosate-resistant gene displayed similar or higher composite fitness compared with that carrying glufosinae-resistant gene.Seeds of backcross generations were buried at 3cm and 15cm depth in soil in order to test the maintenance of seed vitality.The results indicated that between 51%and 76%seeds of BC1F7-8,BC2F6-7 and BC3F5-6 kept viability after buried in 3 cm-depth field for 10 months,and between 66%and 83%seeds of BC1F7-8,BC2F6-7 and BC3F5-6 kept viability after buried in 15 cm-depth field for 10 months.These seeds had a potential to become volunteers in field.Therefore we should avoid to backcross between FI(herbicide-resistance GM oilseed rape and wild B.juncea)and wild B.juncea again and to minimize seeds spread of backcross generation in order to reduce ecological risk induced by herbicide-resistance GM oilseed rape. |
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