美国转基因玉米的生产概况和发展趋势

美国是世界上最大的玉米生产国, 种植面积、总产和单产均居世界首位。转基因玉米自1996年引入生产以来，使玉米生产上了一个新台阶。当前推广利用的转基因玉米品种基本上是抗虫和抗除草剂两种类型。抗虫是由在玉米体内表达Bacillus Thuringiensis(Bt)毒素结晶蛋白(cry蛋白)基因所致，除草剂的抗性(Herbicide tolerance, HT)是由外源的或改良的EPSPS基因在玉米体内表达来实现。转基因玉米的种植面积每年都稳步上升，转基因玉米的也由单一的Bt或HT转变为多基因多性状的叠加，将抗玉米螟和抗Rootworm结合，使玉米的地上部和地下部都得到了有效的保护，再加之抗除草剂基因的叠加，使得转基因品种在生产上更具竞争力。转基因玉米的抗虫和抗除草剂等优良性状带来了巨大的经济和环境效益, 并被越来越多的大众所接受。转基因玉米在短短10年间的应用和发展，还不能回答转基因作物对人类和环境的长期影响等问题。因此，对转基因作物的管理和利用仍不能掉以轻心，不能因对生物技术的热情而对人类和环境造成无意的不可挽回的破坏。

Application and Trends of Transgenic Corn in the U.S.

The United States is the number one country in the world in terms of total corn acreage, total corn production and unit yield. Corn yields have been further improved by the introduction of transgenic corn varieties since 1996. The two major transgenic corns are insect-resistant and herbicide-resistant corns. Insect resistance was achieved by expressing in corn cry genes from Bacillus Thuringiensis(Bt) and herbicide tolerance by expressing either modified EPSPS or EPSPS from agrobacterium strain CP4. In the past ten years, transgenic corn acreage has grown steadily, and transgenic corn varieties have been improved from single transgenic traits to double and multiple traits stacked together. Transgenic corn has been proven successful in fighting insects, reducing pesticide application and increasing yield. However, issues about genetically modified organisms' long term effects on human health and environment still remain, and more research and studies are still needed.