| Commercial release of herbicide-resistant GM rice may bring a series of environmental safety issues. One of the main concerns is the risks of transgenes dispersal to weedy rice through pollen. The initial hybridization between transgenic rice and weedy rice has been confirmed by numerous studies. Therefore, we should concern for the fitness of hybrids with transgene in the natural environment. The probability of transgene establishment into compatible relatives is very dependent upon the fitness of the F1hybrid and the subsequent generations. Therefore evaluating the fitness of hybrids is an important aspect to assess the potential ecological risks of genetically modified crops. In this paper, F1, F2, F3hybrids between japonica glufosinate-resistant GM rice Y0003and six different weedy rice accessions (two japonicas from Dandong and Shenyang; four indicas from Taizhou, Changzhou, Zhanjiang and Zhaoqing) and F3hybrids between indica glufosinate-resistant GM rice86B and the same six accessions of weedy rice were researched on fitness under transplanting and direct-seeding methods with the presence or absence of herbicide selection pressure in the field condition of Nanjing. The tendency of fitness among successive generation of hybrids were analyzed. The dormancy and ability of survival over winter in the field of the seeds of hybrids were also investigated. The potential environmental risks of hybrids were predicted according to the above research results comprehensively. The main results were as follows:1. Fl hybrids derived from controlled crosses between six weedy rice and transgenic rice line were resistant to glufosinate. All F1hybrids displayed heterosis or had similar values for height, flag leaf area, culm diameter, panicle length and100-seed weight, compared with their respective parental weedy rice. In transplanting fields, the fitness of two japonica-japonica F1hybrids (F1DD, F1SY) and one of indica-japonica F1hybrids (F1ZQ) were significantly higher than their respective weedy rice, and the fitness values of the other three F1hybrids were similar to their respective weedy rice. In direct-sowing fields, the fitness of F1SY was greater than WRSY, the fitness of F1DD and F1ZQ had no significant difference with their respective weedy rice, and the other three F1hybrids had lower fitness value than their respective weedy rice. F1hybrids demonstrated a strong advantage on tiller numbers per plant, panicle numbers per plant and seed shattering rate compared with the transgenic rice Y0003. The fitness of Fl hybrids were greater than Y0003or at the same level as Y0003.2. About64.7%of F2ZJ survived under glufosinate selection, deviated from the expected3:1Mendelian segregation, and the other five F2hybrids followed a normal3:1Mendelian segregation. The fitness of F2DD and F2SY were significantly greater than their respective japonica weedy rice. However, the fitness of F2TZ,F2CZ, F2ZJ and F2ZQ were significantly lower than or similar to their respective weedy rice. The fitness of all of the F2hybrids was higher than or similar to the transgenic cultivated riceY0003, except that F2DD, which had a lower fitness value in absence of glufosinate selection pressure in the transplanting field.F2SY、F2TZ、F2CZ、F2ZJ presented greater fitness compared with their respective F1hybrids, while F2DD and F2ZQ had similar fitness to their respective F1hybrids. The two japonica-japonica F2hybrids seeds didn’t have dormancy, and the four indica-japonica F2hybrids seeds were similar in dormancy to their respective weedy rice. The seed survival test showed that about9%,64%and54%seeds of F2DD, F2TZ and F2ZQ respectively survived after having been buried for5months.3. About68.9%of F3CZ survived under glufosinate selection, deviated from the expected5:1Mendelian segregation, and the other five F2hybrids followed a normal5:1Mendelian segregation. The japonica-japonica F3hybrids (F3DD and F3SY) exhibited greater fitness values in both transplanting and direct-seeding. F3ZJ and F3ZQ in transplanting plots had the higher fitness, F3CZ and F3ZQ in direct-seeding plots had the lower fitness than their respective weedy rice. The fitness of the rest indica-japonica F3hybrids had no significant difference with that of their respective weedy rice. In glufosinate selection pressure, Fitness of F3hybrids showed superiority compared with Y0003except that F3CZ, which has similar fitness to Y0003in direct-seeding field. However, in absence of glufosinate selection pressure, only F3ZJ hybrids had greater fitness value than Y0003, the other five experimental F3had similar fitness to Y0003.There is no significant difference between the fitness of F3SY and F2SY, the fitness of the rest five types of F3were improved compared with that of the corresponding F2. Although the dormancy and survival of F3hybrids were weaken compared with F2hybrids seeds, some of F3hybrids seeds still survived over winter in nature.4. Among the F3hybrids between transgenic rice86B and each of six different weedy rice accessions, F3DD, F3TZ and F3ZQ for glufosinate resistance fitted a5:1Mendelian segregation.65.3%-71.1%of F3SY, F3CZ and F3ZJ showed resistance to glufosinate, deviated from the expected5:1Mendelian segregation.The fitness of all F3hybrids were significantly higher than or similar to their respective weedy rice. With the presence of glufosinate pressure, there is no significant difference on fitness between each of the two japonicas-indicas F3and86B, the rest of F3hybrids displayed obvious advantages compared with86B. With the absence of glufosinate pressure, the fitness of F3ZJ was significantly higher than that of86B and the rest five F3hybrids had similar fitness values to86B.In summary, hybrids between transgenic rice and the same type of weedy rice could be potentially more fit and pose a higher ecological risk than their respective parents. Therefore, it is particularly need to prevent the gene drift from transgenic cultivated rice to weedy rice before its’environmental release. Meanwhile, the ecological risks of hybrids between transgenic rice and the different type of weedy rice shouldnot be ignored. From above the results, it is implied that the most important factor to affect the fitness of hybrids is the genetic background of parents. Furthermore, the planting methods and the herbicide selection pressure will also affect the fitness of hybrids. |
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