Impact Of Insect-resistance Transgene Bt/CpTI On Fitness Of Different Crop-weedy Rice F₂Progeny

Research and development of insect-resistant transgenic cultivated rice provides benefit for rice production, which offers a good opportunity for the ensuring of China’s food security. But the undesired ecologic effects brought by the transgene have aroused widely concern worldwide. Weedy rice is a kind of con-specific weeds of cultivated rice, and is one of the three most noxious weeds co-existing in paddy rice fields. These years as the transform of cultivation form from transplanting to direct seedling in some of the rice planting regions, acompanied by the lack of field management, the density of weedy rice is increasing year by year, which brings great harm to rice cultivation and production.It is shown that genes from cultivated rice can pass on to weedy rice via gene flow, and escaped transgene can express normally in rice population, thus whether the insect-resistant transgene can fixed and spread in weedy rice populations mainly depends on its fitness effects. Analysis of fitness effects of transgene under different environmental is important for the prediction and control of transgene escape.Fitness of a transgene can measure the ability of the gene adapting to the environment and the ability to produce fertile offsprings, and it can be influenced by the characteristics of transgenes, the genetic backgrounds of the populations, the natural environmental conditions.Previous study is limited about the ecologic impacts of insect-resistant transgenes flow from cultivated rice to its wild relatives. Given that rice has pivotal position in the world food production, and insect-risistant transgenic rice is waiting for commercial production, in-depth study about the fitness effects is very important.For better assessment of the fitness effects of different factors such as insect-resistant transgenes, the genetic backgrounds of weedy rices, and planting patterns, we used five weedy rice strains collected from the world’s different cultivated rice-growing areas, with large phenotypic and genetic differences, we got F1hybrids with the transgenes (Bt/CPTI) through artificial hybridization and then the F2progeny by self-pollination, which included its progeny with or without the transgenes, they are basically the same except for the transgenes, thus the influence of differences in genetic backgrounds on the results can be excluded. It is feasible to assess the fitness changes of the weedy populations brought only by the transgenes. In addition, we set up differential insects-control methods, and used different density cultivation modes of weedy rices under different tillage patterns, which can help better understand the cultivation modes effects on fitness.The purposes of this experiment are to:(1) compare fitness change of F2populations with or without the transgenes under different insect-control methods;(2) assess fitness effects of different cultivation modes (pure, mixed and dense-mixed);(3) analyze the impact of different weedy rice genetic backgrounds (strains) on transgene fitness. The experimental results show that:1. Compared with the F2populations without the transgenes, those contain the transgenes can bring fitness advantages under higher level of insect pressure, mainly on number of seeds per plant and plant height. Three-way ANOVA results show that the presence of insect-resistant transgenes had significant effects on insect pressure of the population and fitness-related traits.2. Different cultivation modes had significant impact on nearly all fitness related traits except for seed set and insect pressure. Under dense-mixed cultivation mode (15cm×15cm), the major traits we measured such as number of tillers, panicles per plant, number of seeds showed poor performances compared to mixed mode (20cm x20cm). Besides, Fitness difference brought by the transgenes is amplified to a certain extent:with increase in planting density, differences were more obvious in F2containing the transgenes than those had no transgenes. These results indicate that different cultivation modes would influence fitness effects.3. Weedy rices with different origins performed differently in insect-resistant ability, and three-way ANOVA also demonstrated significant influences on insect index and nearly all fitness-related traits in the experiment by different weedy backgrounds, suggesting that when assessing the ecological impact of gene flow, we must consider that genetic variation in recepients may affect the natural selection, thus a case-by-case analysis should be followed for different genetic backgrounds.In addition, no significant interaction is found among transgenes, weedy rice backgrounds, and cultivation modes, which told us that those three factors may play independent role in influencing insect pressure and fitness-related traits of the populations. In this study, we used F2progeny of five weedy rice strains and compared the fitness effects of F2with and without transgenes under different cultivation modes and insect-control measures. The following conclusions are made. First, the insect-resistant transgenes can bring fitness benefit to F2progeny in relatively high insect pressure environments. Second, fitness witness difference influences in different cultivation modes. Third, the fitness effects of insect-resistant transgenes are affected by different genetic backgrounds of weedy rice. Consequently when assessing the fitness effects of gene flow, we should take all factors that influences fitness into consideration. Results of this study will provide valuable information to assessment of the ecological impacts of transgenic escaped.