| Much attention has been focused on the issue of gene flow from transgenic herbicide-resistant oilseed rape to wild relatives or sexual compatible weeds. Although there are many reports on fitness of backcross generation between transgenic oilseed rape and weedy or wild relatives, there is no clear evidence that the backcross generation carrying resistant gene between wild B. juncea and genetically modified oilseed rape could survive in natural environment. The probability of transgene establishment into another species depends highly on the fitness of the F1 hybrid between a crop and a wild species and the subsequent generations. Fitness may be defined as the relative ability of an individual to survive and successfully reproduce in a given environment, with the most fit leaving the greatest number of offspring. The fitness of inter-and intra-specific plant hybrids depends on not only the transgene, but also the parental genetype, testing environment and their interactions.We obtained the backcross generation between four populations of wild Brassica juncea (Xi'an and Qinghai populations, glyphosate susceptible, Maoshan and Nantong populations, glyphosate tolerant to 675g a.e.ha-1), and transgenic glyphosate-resistant oilseed rape. We measured the frequency of the glyphosate-resistant gene from transgenic oilseed rape across backcross generations under the press of herbicide selection pressure and the backcross generation's fitness components of vegetative growth (plant height, diameter of plant rosette, chlorophyll fluorescence, stem diameter, the first branch number), and reproductive growth (silique length, silique number/plant, seed number/silique, total seed weight and kernel weight) under greenhouse and filed condition. The surviving propability of backcross generations carrying glyphosate-resistant gene under benigh and natural environment was analyzed. The main results were as follows: As for the first backcross generation (BC1),26.3-60.6% reciprocal of BC1 expressed glyphosate resistance and survived under selecting by 1500g a.i.ha-1glyphosate. In greenhouse, composite fitness of reciprocal BC1 of Xi'an and Qinghai, and BC1 using Maoshan wild B. juncea as paternal plants were significantly lower than their respective wild B. juncea. But reciprocal BC1 of Nantong and BC1 using Maoshan wild B. juncea as maternal plants showed similar fitness to their respective wild B. juncea. Four BCl using wild B. juncea as maternal plants showed similar fitness and had no significant difference. Four BC1 using wild B. juncea as paternal plants, composite fitness of Xi'an was much higher than that of Maoshan and Nantong. Composite fitness of BC1 using Maoshan wild B. juncea as maternal plants was much larger than BCl using Maoshan wild B. juncea as paternal plants. The results demonstrated that glyphosate-resistant gene from transgenic oilseed rape maintained across the four first backcross generations. The establishment propabilities of BC1 of Maoshan and Nantong populations were similar to respective wild B. juncea on benigh environment. Backcross direction and genetype had an effected on fitness of BC1.55.6-98% of the first offspring of BC1 and 44.4-82.4% of BC2 expressed glyphosate resistance and survived under selecting by 1500g a.i.ha-1 glyphosate. In greenhouse, composite fitness of the first offspring of Xi'an reciprocal BCl and the first offspring of BC1 using Maoshan wild B. juncea as paternal plants was lower than their respective wild B. juncea. The other first offspring of BC1 showed similar fitness to their respective wild B. juncea. All BC2 demonstrated similar fitness to their respective wild B. juncea. Composite fitness of Xi'an and Qinghai BC2 using wild B. juncea as paternal plants was much larger than that of BC2 using wild B. juncea as maternal plants. Composite fitness of Maoshan and Nantong reciprocal BC2 were similar. All BC2 using wild B. juncea as maternal plants didn't showed fitter than the first offspring of BCl using wild B. juncea as maternal plants. BC2 using Xi'an, Qinghai, Maoshan wild B. juncea as paternal plants behaved better than their respective the first offspring of BC1.In field, fitness of the first offspring of Xi'an BC1 was much lower than that of wild B. juncea. Fitness of the other first offspring of BC1 were similar to or higher than their respective wild B. juncea. The fitness of all reciprocal BC2 were similar to or or higher than their respective wild B. juncea, especially the BC2 using Qinghai, Maoshan wild B. juncea as paternal plants, which were significantly larger than their respective wild B. juncea. The results suggested near 50% or more than 50% of the first offspring of BC1 and BC2 survived under selecting by 1500 g a.i.ha-1 glyphosate. The glyphosate-resistant gene from transgenic oilseed rape maintained across the first offspring of BC1 and BC2. The fisrt offspring of Qinghai, Maoshan and Nantong BC1 and four populations'BC2 could establish on benigh condition and natural environment.Compared the fitness of the first offspring and BC2 of four populations, the first offspring of four populations BC1 showed similar fitness but the fitness of BC2 differed in greenhouse and filed conditions. In field condition, fitness of Maoshan BC2 was the highest in all BC2. It was concluded that the genetype and the environmental conditions effected the fitness. The establishing propability of glyphosate-resistant gene in Maoshan population was much higher.For Xi'an population, composite fitness of the first offspring of BC1 was much lower than wild B. juncea, but BC2 didn't show differences with its wild B. juncea at 5 plants/m2. composite fitness of the first offspring of BC1 and BC2 were all similar with its B. juncea at 10 plants/m2. For Maoshan population, BC2 using wild B. juncea as paternal plants demonstrated higher fitness than the first offspring of BC1 at 5 plants/m2. But there were no difference among all BC at 10 plants/m2. From above results, we concluded that the density had an effect on competition of different populations of BC generation. But further study should be done in order to explore the effects of density on fitness of BC generation.Finally, we also measured Nantong population's fitness components in mixed planting mode. Under 1:1:1:1:1:1:(transgenic oilseed rape:wild B. juncea:the first offspring of BC 1 using wild B. juncea as maternal plants:the first offspring of BC1 using wild B. juncea as paternal plants:BC2 using wild B. juncea as maternal plants:BC2 using wild B. juncea as paternal plants), BC2 using wild B. juncea as maternal plants demonstrated higher fitness than its wild B. juncea and the first offspring of BC1. Under 3:1:1:1:1:1, fitness of BC2 using wild B. juncea as paternal plants was significantly higher than oilseed rape, wild B. juncea and other BC generations. Therefore, BC2 using Nantong wild B. juncea as paternal plants should be pay much attention. The effect of density and frequency on fitness need further experiments under field condition. |
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