Study On Fitness Of Backcross Generations Between Two Herbicide-Resistant Transgenic Oilseed Rape And Wild Brassica Juncea

One of the concerns about releasing genetically modifed herbicide-resistant (GMHR) crops is that herbicide-resistant (HR) transgenes may escape from GMHR crops to their weedy relatives through pollen flow. If this happens, weeds with the HR trait might produce new problems for weed control. Therefore, predicting potential gene flow from GMHR crop to weed species before GMHR crops are released into the environment is necessary. Many researchers have reported that transgenic oilseed rape(Brassica napus) may hybridize with many of its related wild plants spontaneously, including with wild B. juncea. And there are many documents on fitness of backcross generations between transgenic oilseed rape and wild or weed relatives. However, continuous tracking research on inheritance of transgene in backcross generations of different transgenic herbicide-resistant oilseed rape varieties and wild Brassica juncea, and fitness of these backcross generations with transgene in greenhouse and in field are lacked. Therefore, the second, the third and the fourth progeny of the first backcross generation(BClF2, BC1F3, and BC1F4), the first, the second and the third progeny of the second backcross generation (BC2F1,BC2F2,BC2F3), the first, the second progeny of the third backcross generation (BC3F1,BC3F2) of transgenic glyphosate-resistant oilseed rape (DS-Roughrider, Roundup Ready, event RT73)or glufosinate-resistant oilseed rape(Swallow, Liberty Link, event HCN92) and wild B. juncea were researched on inheritance of herbicide-resistant gene and fitness in greenhouse and in field in different densities and planting proportions. Furthermore, the difference on potential introgression of two herbicide-resistant gene of two different transgenic oilseed rape varieties to wild B. juncea were also discussed. The main results are as follow:1. The germination percentages and inheritance of herbicide-resistant gene of BC progeniesThe germination percentages and the frequency of transgenes transfer in BC1F2-4, BC2F1-3, BC3F1-2 were researched. The results showed that, for glyphosate-resistant oilseed rape, the germination percentages of BC1mF2-4and BC1pF4 were similar to that of wild B. juncea. while the germination percentages of BC1pF2and BC1pF3 were 87%,92.97% respectively, lower than that of wild B. juncea significantly. However, for glufosinate-resistant gene oilseed rape, the germination percentages of BC1mF4 were similar to that of wild B. juncea. The germination percentages of other progenies were from 86-93%, lower than that of wild B.juncea significantly.For glyphosate-resistant oilseed rape, BC2F1 and BC3F1 followed a normal 1:1 Mendelian segregation. BC2F2 and BC3F2 followed a normal 3:1 Mendelian segregation. The other BC generations deviated from the expected Mendelian segregation. For glufosinate-resistant gene oilseed rape, all experimental backcross generations deviated from the expected Mendelian segregation. The herbicide-resistant plant percentages of backcross generations increased with the increasing of the self-pollination times. However, the percentages of glyphosate-resistant plants were much higher than that of glufosinate-resistant plants in backcross generations.2-Fitness of backcross generations between two transgenic oilseed rape varieties and wild B.juncea in greenhouseThe composite fitness of BC1F2, BC1F3, BC2F1, BC2F2 between two transgenic oilseed rape varieties and wild B.juncea were studied under greenhouse conditions. We measured the fitness components of vegetative growth including plant height, stem diameter, diameter of plant rosette, the first branch number/plant, chlorophyll fluorescence, above-biomass, and the fitness components of reproductive growth including pollen viability, silique number, silique length and seed number/silique.The results demonstrated that the composite fitness of backcross generations had no significant differences with that of wild B.juncea. However, the most backcross generations still did not produced as many seeds per silique as did self-pollinated wild B. juncea. The plants of BC1F2, BC1mF3 with lower seed setting rate and BC1pF3 with glyphosate-resistant gene produced less seeds per silique than wild B. junce. While the plants of BC1mF3 with higher seed setting rate, BC2F1 and BC2F2 with glyphosate-resistant gene produced as many seeds per silique as did wild B. junce. However, the backcross generations with glufosinate-resistant gene, except for BC2mF1, which produced as many seeds per silique as did self-pollinated wild B. juncea, produced less seeds per silique (2.09-9.91) than didn’t wild B. junce.3. Fitness of backcross generations between two transgenic oilseed rape varieties and wild B. juncea in fieldThe fitness components of BC1F3, BC2F2 between two transgenic oilseed rape varieties and wild B juncea in field under different densities and different planting proportions were measured. The ability of survival over winter in the field of the seeds of backcross generations was also investigated.The results showed that, in pure plots, the backcross generations at different density and planting proportion had significant lower composite fitness than wild B. juncea, except for BC2mF2 with glyphosate-resistant gene at low density, which had no significant differences with that of wild B juncea. The BC1pF3 with glufosinate-resistant gene had lowest composite fitness (0.67). In mixed plots, all experimental backcross generations at different densities and planting proportions had significant lower composite fitness than wild B. juncea. The composite fitness difference between BC2F2 with glyphosate-resistant gene and wild B. juncea was least. And BC2F2 with glyphosate-resistant gene had significant higher composite fitness than BC1F3 with glufosinate-resistant gene. But the values of silique number per plant, above-biomass and seeds weight per plant of backcross generations at high density plots were less than at low density plots. The germination percentages of backcross generations decreased from initial 80% to 60% eight months after being buried, and decreased gradually to close to 30% in May next year. The germination percentages of backcross generations did not differ with wild B. juncea.From the above results, the inheritance of the two herbicide-resistant genes from different transgenic oilseed rape in backcross generations differed significantly. The glyphosate-resistant gene from transgenic glyphosate-resistant oilseed rape was transferred to its backcross generations more easily than did glufosinate-resistant gene from transgenic glyphosate-resistant oilseed rape. The backcross generations with glyphosate-resistant gene had higher composite fitness than the backcross generations with glufosinate-resistant gene. And composite fitness of backcross generations increased with their self-pollination to close to that of wild B. juncea. The seeds of all backcross generations survived after having been buried for 10 months. And had the potential of weediness.