Changes in pedigree backgrounds of Pioneer brand maize hybrids widely grown from 1930 to 1999

Surveys of pedigree usage indicate that breeding programs can generate genetic diversity in time. There are also concerns that genetic diversity is being lost. Previous studies of pedigree usage in U.S. maize (Zea mays L.) production have reviewed usage of publicly bred inbred lines. However, proprietary inbred lines were already contributing over 90% of U.S. maize production by 1985. This chronological study of germplasm usage compliments previous studies of genetic diversity in U.S. maize production by reporting the pedigree backgrounds of 68 proprietary, widely used maize hybrids released by Pioneer Hi-Bred International during the period 1930 to 1999. Objectives are to identify founder sources for the hybrids and to reveal changes in founder contributions through time. We also compare founder usage with pedigrees of widely used U.S. public inbred lines to measure the extent of their reliance on common germplasm backgrounds. Pedigrees of the hybrids collectively traced to at least 61 founders. Several founders of the hybrids had complex pedigrees. Founder backgrounds of the hybrids could be traced to at least 22 landraces with additional contributions from other populations or landraces. Public lines used for comparison traced to 14 founders. Nine founders of the public lines were common in the era hybrids; five were unique to the public lines. Differences in founder contributions were evident for the era hybrids and the public lines. Significant contributions from both the private and public sectors were evident in the pedigrees of the era hybrids. Diversity in time was evident. Hybrids tended to associate by decade of initial release. Most new founder contributions occurred in the 1940s (35%), 1960s (36%), and 1980s (20%). Breeding networks have allowed germplasm that was once exotic to the central Corn Belt to contribute improved productivity in that region.