Morphological Changes in Parental Lines of Pioneer Brand Maize Hybrids in the U.S. Central Corn Belt

We observed changes over time (1930-2007) for 38 morphological characteristics by examining 78 parental inbreds of hybrids that have been used to measure genetic gain in maize (Zea mays L.) in the central Corn Belt of the United States. Fifty-eight percent of the characteristics changed as new inbreds were successively bred during this period. More recently, during the era of single-cross hybrids, changes occurred for several characteristics either at differential rates or in opposite directions, depending on whether inbreds were used as female or male parents. Founder contributions by pedigree also changed in time and according to usage as females or males in single-cross hybrids. Further conscious selection on some of these characteristics might expedite further improvements in rate of genetic gain.