| Transgenic herbicide-resistant trait has been the main resistant traits of genetically modified(GM)crops,since it was globally released.Herbicide-resistant transgenes may escape from genetically modified herbicide-resistant(GMHR)crops to their wild relatives and cause environmental problem,which have been widely concerned.Brassica napus is one of the main commercial cultivated GMHR crops.It has been confirmed that transgenic oilseed rape(Brassica napus)hybridized with its wild relatives spontaneously,including wild B.rapa,B.juncea,Raphanus raphanistrum and B.juncea var.gracilis.And researches related to frenquecy of gene flow,inheritance of transgene and fitness of hybrids or backcross generations between transgenic oilseed rape and wild or weed relatives have been conducted.However,continuous tracking researches on inheritance of transgene in backcross generations of glyphosate-resistant oilseed rape and wild B.juncea,and fitness of these backcross generations with transgene in greenhouse and field are lacking.On the basis of previous studies,the fourth,the fifth of the first backcross generation(BC1F5,BC1F6),the third,the fourth of the second backcross generation(BC2F4,BC2F5),the second,the third progeny of the third backcross generation(BC3F3,BC3F4)of transgenic glyphosate-resistant oilseed rape(DS-Roughrider,Roundup Ready,event RT73)and wild B.juncea were researched on inheritance of herbicide-resistant gene.Furthermore,the fitness of BC1F4-5,BC2F3-4,BC3F2-3 in greenhouse and in field in different densities and planting proportions were researched.The main results are as follow:1.The germination rate and inheritance of transgene in Backcross progeniesThe emergence rates and glyphosate-resistant transgene inheritance of BC1F5-6,BC2F4-5,BC3F3-4 between glyphosate-resistant oilseed rape and wild B.juncea were studied.The results showed that,the emergence rates of these progenies were between 87%and 93%,which were similar to that of wild B.juncea.The results implied that the emergence of these progenies did not showed weakness compared with that of B.juncea.After spraying with 1400 g a.i.ha-1 glyphosate,the percentage of surviving plants in diferent backcross generation were as follow:BC1mF5 and BC1pF5 were 96.21%and 93.01%,BC1mF6 and BC1pF6 were 98.63%and 94.88%,BC2mF4 and BC2pF4 were 90.13%and 93.53%,BC2mF5 and BC2pF5 were 91.99%and 96.61%,BC3mF3 and BC3pF3 were 92.36%and 79.55%,BC3mF4 and BC3pF4 were 86.06%and 86.16%.The results demonstrated that glyphosate-resistant gene were transferred to these backcross generations with high frequencies.But transgene inheritance in backcross generations deviated from the expected Mendelian segregation except for BC2mF4,which followed a normal 9:1 Mendelian segregation.2-Fitness of backcross generations between transgenic oilseed rape and wild B.juncea in greenhouseThe composite fitness of BC1F4-5,BC2F3-4 and BC3F2-3 carring glyphosate resistance 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,the plant height of BC1F4-5,BC2F3-4 were significant lower than that of wild B.juncea,and the other fitness components of BC1F4-5,BC2F3-4 were similar to that of wild B.juncea.All the fitness components of BC3F2-3 were similar to that of wild B.juncea.The composite fitness of BC1F4,BC2F3 and BC3F2 were among 0.97 and 1.04,and were similar to that of wild B.juncea.The composite fitness of BC1F5,BC2F4 and BC3F3 were among 0.96 and 0.99,and were also similar to that of wild B.juncea.The above results showed that BC1F4-5,BC2F3-4 and BC3F2-3 had similar composite fitness to wild B.juncea in greenhouse.The backcross direction did not affect the composite fitness of these backcross generations.3.Fitness of backcross generations between transgenic oilseed rape and wild B.juncea in fieldThe fitness components of BC1F4-5,BC2F3-4 and BC3F2-3 between transgenic oilseed rape and wild B.juncea in field under two densities and four different planting proportions were measured.The seeds survival ability of backcross generations in field was also investigated.When BC1F4,BC2F3,BC3F2 were planted in pure plots in 2013,the composite fitness of BC1F4?BC2F3 were significant lower than that of wild B.juncea at two densities,and BC3F2 was similar to that of wild B.juncea.When BC1F4,BC2F3,BC3F2 were planted at the 4:1 propotion,the composite fitness of BC1F4,BC2F3 and BC3F2 were significant lower than that of wild B.juncea at two densities.When BC1F4,BC2F3,BC3F2 were planted at the 3:2 and 1:1 propotion,the composite fitness of BC1F4,BC2F3 were significant lower than that of wild B.juncea,and BC3F2 were similar to that of wild B.juncea at low density;the composite fitness of all backcross generations were significant lower than that of wild B.juncea at high desity.When BC1F5,BC2F4,BC3F3 were planted in pure plots in 2014,the composite fitness of all backcross generations were also similar to that of wild B.juncea at low density.But at high density,the composite fitness of BC1F5,BC2pF4 were significant lower than that of wild B.juncea and BC2mF4,BC3F3 was similar to that of wild B.juncea.When BC1F5,BC2F4,BC3F3 were planted at the 4:1,3:2 and 1:1 propotion,the composite fitness of BC1F5,BC2pF4 were significant lower than that of wild B.juncea at two densities,while BC2mF4,BC3F3 were similar to that of wild B.juncea.From the above results,the composite fitness of BC1F4 and BC2F3 was significant lower than that of wild B.juncea under different plant conditions.It implied that BC1F4 and BC2F3 could not establish population in natural condition as wild B.juncea as did.However,planting density and propotion affected the composite fitness of BC3F2 significantly.In second year,the composite fitness of BC1F5 and BC2pF4 were significantly lower than wild B.juncea except for in pure plot at low density.The composite fitness of BC2mF4 and BC3F3 was similar to wild B.juncea at two densities and different propotions.It implied that planting density and propotion did not affect their fitness significantly.The backcross generations seeds were buried at 3cm and 15cm depth in soil in order to test the maintenance of seed vitality.The results indicated that,more than half and more than 60%of seeds of BC1F5,BC2F4 and BC3F3 kept viability after buried for 11 months in soil at 3cm depth and 15cm depth,respectively.The seed viabilities of backcross generations were similar to that of wild B.juncea.More than 36%and more than 70%of BC1F6,BC2F5 and BC3F4 kept viability after buried in soil for 9 months at 3cm and 15cm depth respectively.From the above results,more than 36%seeds of the backcross generations survived after buried in field for 9 months,and seeds kept higher seed viability buried in 15cm than in 3 cm depth in soil.It was concluded that the glyphosate-resistant gene transferred to BC1F5-6,BC2F4-5 and BC3F3-4 backcross generations with more than 79.55%frequency.The composite fitness of all the backcross generations was similar to that of wild B.juncea in greenhouse.The composite fitness of the backcross generations obtained by 2 times backcross and 3 times self-pollination,3 times backcross and 1 time self-pollination were similar to that of wild B.juncea in field.More than 36%seeds of the BC1F5-6,BC2F4-5,BC3F3-4 survived after buried in field for 9 months.Therefore the backcross generations had the potential of weediness in natural environment. |
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