| One of the concerns about releasing genetically modified herbicide-resisitant (GMHR) rice is that herbicide-resistant transgenes may escape from GMHR rice to their weedy relatives-weedy rice through pollen flow. If this happens, weedy rice with the herbicide-resistant trait might produce new problems for control. Therefore, predicting potential gene flow from GMHR rice to weedy rice before GMHR rice released into the environment is necessary. In order to assess the risk of gene flow from glufosinate-resistane transgenic hybrid rice125S/Bar68-1, produced by the Institute of Subtropical Agriculture of the Chinese Academy of Sciences, to weedy rice, the gene flow frequency was determined using the concentric circular and alternating cultivation design. The effective spraying period and dosage in herbicide application are keys for ensuring high and stable yield, therefore it is necessary to research on herbicide application techniques in herbicide-resistant transgenic rice field, including spraying period and dosage. The herbicide application techniques in glufosinate-resistant transgenic rice Y0003direct-seeding and transplanting field was explored. The main results are as follows:1. Gene flow from glufosinate-resistant transgenic hybrid rice125S/Bar68-1to weedy rice and conventional cultivated riceUnder concentric circular cultivation condition, the glufosinate-resistant transgenic hybrid rice125S/Bar68-1was used as pollen donor and six weedy rice accessions (WRCS, WRZQ, WRTZ, WRCZ, WRSY, WRGL) and conventional cultivated rice CR204as pollen recipients, the distance and frequency of gene flow from pollen donor to pollen recipients were measured. The results indicated that the maximum transgene flow from transgenic hybrid rice125S/Bar68-1to seven recipients occurred at1m in the prevailing wind direction and was highest (0.302%) with WRCS, and the lowest transgene flow of0.011%occurred with WRCZ at12m for the donor in the prevailing wind direction. The gene flow frequency declined considerably with increasing distance from the pollen source for all recipients. The maximum distance at which gene flow was detected was14m for the donor in the prevailing wind direction (for WRCS). By the result of gene flow frequencies at different geographic locations, a clear asymmetric distribution with hybridization event favored in plants placed under the local prevailing wind direction for both weedy rice and conventional rice. Correlation analysis showed that the gene flow frequency was significant relevant to the flowering overlap duration between the pollen donor and recipients. This study revealed that there were potential gene flow from glufosinate-resistant hybrid rice125S/Bar68-1to weedy rice and cultivated rice, and the risk of gene flow to WRCS was highest, and lowest to WRGL. Therefore, the gene flow from glufosinate-resistant hybrid rice125S/Bar68-1must take a prevention measure after large-scale environmental release.Under alternating cultivation condition, the glufosinate-resistant transgenic hybrid rice125S/Bar68-1was used as pollen donor and two weedy rice accessions (WRCS and WRTZ) as pollen recipients, the transgene flow frequencies were detected. More than20000seeds were randomly selected from the four replicates of each harvested recipient (WRCS and WRTZ) overlapping in flowering with the transgenic donor.28and34seedlings carrying the transgene came from WRCS, which overlapped in flowering period with the first batch and the second batch of transgenic rice, respectively;32seedlings carrying the transgene came from WRTZ, which overlapped in flowering period with the second batch of transgenic rice. The average frequency of gene flow from the first and second batch of transgenic rice to WRCS was0.402±0.055%,0.470±0.065%, respectively. The average gene flow frequency of from the second batch of transgenic rice to WRTZ was0.395±0.039%. Correlation analysis indicated that the longer flowering overlap duration (FOD) of the pollen recipients with the pollen donor resulted in increased gene flow frequency significantly. There were high probability of gene flow from glufosinate-resistant hybrid rice125S/Bar68-1to weedy rice; therefore, some measures must be taken to reduce the risk of gene flow before large-scale environmental release or commercial planting of glufosinate-resistant hybrid rice125S/Bar68-1.2. Bioassay on effect of weed control and safety of glufosinate-resistant transgenic rice by different glufosinate application techniquesThe effect of weed (weedy rice and barnyard grass) control and safety of glufosinate-resistant transgenic hybrid rice125S/Bar68-1were bioassayed in direct-seeding and transplanting rice field by glufosinate application of different dosage at different rice growth stages. The results showed that the weed control efficiency at the dosage of 75ml/667m2was worst (<50%), but the weed control efficiency reached100%at the dosage of150ml/667m2and300ml/667m2whatever the spraying period of3-4leaf stage,5-6leaf stage and1-2tiller stage in direct-seeding rice field. Compared with the weed-free control, the height and yield of transgenic rice were reduced significantly with the glufosinate application of different dosage. The plant height and yield of transgenic rice treated at5-6leaf stage with dosage of150ml/667m2were higher than that treated by the same dosage at other growth stage and different dosage at any growth stage. In transplanting rice field, weed control efficiency at the dosage of75ml/667m2was worst (about50%) whatever spraying period of1-2tiller, booting and heading-blooming stage. The weed control efficiencies of150ml/667m2and300ml/667m2at1-2tiller stage and booting stage were both above90%, but were50%-60%and80%-90%respectively at heading-blooming stage. Compared with weed-free control, the plant height and yield of transgenic rice was not affected at rice booting stage with the dosage of150ml/667m2, while were reduced significantly with the same dosage at1-2tiller and heading-blooming stage, and with the dosage of75ml/667m2and300ml/667m2at any experimental stage.3. The study on glufosinate application techniques in the field of glufosinate-resistant transgenic rice Y0003The effect of different spraying periods (3-4leaf,5-6leaf and tiller rice growth stage) and dosage of glufosinate on weed control and growth of transgenic rice were studied in the direct-seeding field of glufosinate-resistant transgenic rice Y0003. The results showed that the weed control efficiency were low at3-4leaf stage under three experimental dosage,75ml/667m2,150ml/667m2or300ml/667m2. The main reason was due to the competition from subsequent emerged weed, which inhibited growth of transgenic rice and reduced rice yield significantly. Weed control efficiencies of75ml/667m2were low at5-6leaf and tiller stage, and the weed competition inhibited growth of transgenic rice and reduced rice yield seriously, while weed control efficiency of150ml/667m2or300ml/667m2at5-6leaf stage was more than90%, no any injury for rice was observed and the yield of rice increased significantly compared with the weed-free control. However weed competition seriously inhibited the growth of transgenic rice and reduced the rice yield significantly at tiller stage with the dosage of150ml/667m2or300ml/667m2. No matter which spraying period, soil treatment with application of glufosinate at150ml/667m2provided ideal weed control effect, but the yield was reduced because of injuries occurred on the transgenic rice. Therefore the application at5-6leaf stage with the dosage of150-300ml/667m2was recommended for weed control in direct-seeding glufosinate-resistant transgenic rice field. The effect of different spraying periods (5-6leaf and tiller rice growth stage) and dosage of glufosinate on weed control and growth of transgenic rice were studied in the transplanting field of glufosinate-resistant transgenic rice Y0003. The results demonstrated that the weed control efficiencies were low at five-six leaf or tiller stage under the dosage of75ml/667m2, this was due to weed competition which seriously inhibited the growth of transgenic rice and induced rice yield reduction seriously compared with weed-free control. The weed control efficiencies were more than90%, however compared with weed-free control, the growth and yield of transgenic rice were affected at different extent at the dosage of150ml/667m2and300ml/667m2on the two spraying period. In contrast, the yield of transgenic rice treated by the dosage of150ml/667m3at5-6leaf stage was significant higher than the other treatment. The transgenic rice yield was reduced due to injury by soil treatment with glufosinate application of150ml/667m and subsequent weed emergence at the two spraying period compared with weed-free control. Therefore the application at5-6leaf stage with the dosage of150ml/667m2was recommended for weed control in transplanting glufosinate-resistant transgenic rice field. |
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