三、玉米改良现状和发展趋势美国的玉米改良组织完善,分工合理,各种层次的研究都有人负责。目前有玉米育种课题的大学和农业研究机构50多家,还有600多家种子公司,一部分还承担不同规模的育种工作.一些大型种子公司育种试验站的设备和人员甚至超过大学.此外还有与玉米有关的边缘学科,如玉米螟、玉米病害、遗传、生理、推广方面的人员参加玉米育种工作. 当前美国玉米育种的目标,简单地讲是在强秆上结一个好穗。他们从探讨过去50年来玉米达到高产的形态和生理基础出发,重点选择高密植条件下的高产类型,即最适株型或理想型。重视株形紧凑,叶片上冲,秆强,多抗类型的选择。一个简单的方法就是在压力条件(高密植)下选空秆少、倒伏少的类型. Third, the current situation and development of corn improvement The improvement of the organization of corn in the United States, a reasonable division of labor, people at all levels of research. There are more than 50 universities and agricultural research institutes that currently have maize breeding programs and more than 600 seed companies, some of whom also undertake breeding work of different sizes. Some large-scale seed companies have even surpassed universities in their equipment and personnel in breeding test stations. Corn-related marginal disciplines such as corn borer, maize disease, genetic, physiological, and extension personnel are involved in maize breeding. The current goal of maize breeding in the United States is simply to make a good spike on strong stalks. Starting with a discussion of the morphological and physiological basis for high-yielding maize in the past 50 years, they focused on the high-yielding types of plants under high-density conditions, namely the optimum plant type or ideal type. Emphasis on plant shape compact, leaves on the red, straw strong, multi-type anti-choice. A simple method is to select the type of stubble less, lodging less under pressure conditions (high density).