Corn (Zea mays L.) breeding for hybrid development was begun in the early 1900s with the work of Shull (1909), East (1908), and others, but a primitive type of breeding was conducted for thousands of years by the American Indians before the European colonists began settlement in the New World. The U.S. Corn Belt dents were derived from crosses that included germ plasm of the northeastern flint and southern dent or gourdseed types, beginning about 1850, with subsequent selection that developed the U.S. Corn Belt dents. Open-pollinated cultivars, such as Reid Yellow Dent, Krug, Learning, and Lancaster Sure Crop were developed by a type of mass selection that was based on plant, ear, and grain type. This early work, which was done primarily by farmers and seedsmen, provided the germp1asm sources from which were developed the inbred parental lines that were used to produce the first double-cross hybrids used in the USA. Even to the present time, relatively little germ plasm from other countries has been used in corn breeding programs in the USA (Brown, 1975).