Background of U.S. Hybrid Corn

Understanding the history of a crop helps plant breeders select. This historical narrative discusses the background of hybrid corn (L.) in the USA. It attempts to explain why certain open-pollinated cultivars persisted into today's hybrids. Domesticated corn originated by selecting larger, non-shattering ears in tropical, southern Mexico. Corn moved to temperate areas requiring adaptation to more variable, more stressful conditions. Flint corn arrived in the USA about 1000 BC and dent corn arrived after Columbus 2500 yr later. The first southern Corn Belt of the 1830s (Tennessee, Kentucky, and Virginia) moved northwest (Iowa, Illinois, and Missouri) by 1880; shorter-season, more drought tolerant cultivars were developed. About 1000 open-pollinated cultivars resulted from natural and artificial selection in flint × dent backgrounds. A few cultivars were widely adapted and became popular. Virtually all 1000 cultivars became parents of inbred lines. Yellow corn (containing vitamin A) proved better for feeding; white corn production diminished from 50% in 1920 to 1% of total in 1970. Earlier planting, higher plant densities, more nitrogen application, and wider adaptation affected hybrid selection. Pedigree background frequencies of 33 Pioneer Hi-Bred International Inc. proprietary, elite inbred lines directly estimate background Of >40% of U.S. hybrid corn hectarage and indirectly estimate the rest. Forms of ‘Reid Yellow Dent’(‘Iodent Reid’, ‘Troyer Reid’, ‘Osterland Reid’, ‘Stiff Stalk Synthetic’, Reid Yellow Dent per se, and ‘Funk Yellow Dent Reid’) are 50%. ‘Minnesota 13’ is 13%. ‘Northwestern-Dent’ is 5%. ‘Lancaster Sure Crop’ is 4%. ‘Learning Corn’ is 4%. These cultivars were widely adapted and popular. The results are consistent with evolutionary (adaptation) expectations. Genes for adaptedness to the temperate, U.S. Corn Belt (longer days, cooler minimum temperatures, and shorter, drier, more stressful seasons) were naturally and artificially selected; first, in widely adapted, open-pollinated cultivars then, in widely adapted hybrids. Old cultivar and inbred line background sources, few in number, indicate adaptedness is more important than diversity to increase yield.