Impacts Of Insect-Resistant Tansgenes On Fitness Of Cultivated And Weedy Rice

Severe food security problem exists as about 15% global populations are in hunger or undernourishment status. The transgenic biotechnology and the application of genetically modified (GM) crops may be one of the solutions and have made great progress over the last two decades. The insect-resistant GM crop is one of the most important and successful transgenic crops, which occupied about 15% of the total cultivated area and 40% of the total economic benefit by GM crops. Insect-resistant transgenic rice is developed to save yield from the severe damage from insect pest, expecially the stem borers and leaf-rollers. Two certificates were issued to Huahui-1 and Bt-Shanyou-63 (two insect-resistant GM rice lines) by the Ministry of Agriculture in the later 2009, which means the commercial application of insect-resistant GM rice in the near future. However, the commercial cultivation of insect-resistant GM rice also bring some concerns including:(1) how to adjust the agricultural patterns and managements to effectively utilize the GM crops, and (2) the biosafety concerns, such as the transgene escape and its ecological impacts, and their scientific assessments.Wild relatives of cultivated rice, including common wild rice and weedy rice, are distributing among rice cultivation areas in China, which allows the transgene escape through natural hybridization. Once the insect-resistant transgenes escaped into wild/weedy rice populations and altered their fitness, they may cause further ecological risks. Scientific evaluation of the ecological consequences brought by transgene escape requires studying three aspects step by step:(1) the frequency of transgene escape, (2) the expression of transgenes in wild relatives, and (3) the fitness impacts brought by transgenes on wild relatives.Given that researches on transgene escape from cultivated rice to wild/weedy rice were sufficient for determining its freqeuncy, the expression of insect-resistant transgenes in wild/weedy rice and their fitness impacts require serious assessments. Theoretically, the fitness impacts of insect-resistant transgenes contain two aspects:(1) insect-resistant transgenes may bring fitness advantage to rice plant in environments with high target insect pressure, which can be considered as the fitness benefit; (2) insect-resistant transgenes may cause fitness decrease in environments with low target insect pressure, which can be considered as the fitness benefit. To evaluate the fitness benefit-cost effects of insect-resistant transgenes can smooth our knowledge gap from better utilizing of insect-resistant GM rice and environment risk evaluation and regulation.This research, based on the fitness evaluation of insect-resistant transgenes in cultivated and weedy rice, studied the expression of insect-resistant transgenes in cultivated rice and common wild rice in the first and followed by the evaluation of the fitness impacts of insect-resistant transgenes on cultivated rice and cultivated×weedy rice hybrids and its F2 progenies. The main results and findings were exhibited as below:1. The insect-resistant transgene can express normally in cultivated rice common wild rice F1 hybrid and F2 progeny compared with that in cultivated rice, which means the insect-resistant transgene can express normally in wild relatives of cultivated rice once its escape. Consequencesly, it is very necessary to evaluate the fitness change in wild relatives once the transgenes escaped.2. The insect-resistant transgene can provide great fitness benefit when there was considerable level of target insect occurrence, which reflected by the superior yield pefomance of insect resistant GM rice compared with non-GM rice.3. Some insect-resistant GM rice lines had poor yield performance than non-GM rice under low target insect pressure, which means the cryptic fitness cost of insect-resistant transgene. Given the results, the alternately strategic deployment of GM and non-GM rice depending on precise insect prediction can optimize the benefit of GM rice and avoid the cryptic yield loss.4. The non-target insect pests can cause the yield reduction to insect-resistant GM rice and should be controlled when planting the GM rice.5. The insect-resistant transgene also provides great fitness advantage (up to 109%) to weedy rice with the occurrence of target insects, but have no detectable fitness cost in segerated F2 progenies. This result confirmed that the insect-resistant transgene escape from GM rice to weedy rice could lead ecological consequences.6. The fitness enhancement by insect-resistant transgenes under severe insect pressure varied among weedy hybrids derived from different genotypes of weedy rice, suggesting the genetic background of weedy populations may have some impacts on the selective advantage of insect-resistant transgenes.In general, the insect-resistant transgenes can express normally in wild relatives of cultivated rice after its escape and can provide considerable fitness benefit in environmemts with high target insect pressure to weedy rice populations. In further studies, the frequency dynamic of insect-resistant transgenes and transgenic individuals in weedy rice population should be studied.