Maize Germplasm

​A ‘Compilation of North American Maize Breeding Germplasm’ published in 1993 by Crop Science Society of America includes a list of more than 500 distinct, open-pollinated dent and flint varieties that existed in North America. Their locations of origin and use illustrate the varied environments corn occupied in one temperate zone continent. 
 
Adaptation of corn to a wide range of environments included a range of length of growing seasons. This included selections by people for varieties that would flower with minimal accumulation of heat, such as the Gaspe Flint variety used by indigenous people on the Gaspe peninsula in north Eastern Quebec at least as early as the year 1524.  This variety, growing in relatively cool environment, manages to mature with minimum heat units.  If the same variety is grown in Central United States, it matures in only 40-50 days after planting at a height of only 30 inches (76cm).  Tropical hybrids respond to short day lengths rather than heat accumulation to trigger flowering and thus cannot complete a generation in Central USA unless artificially given short days.
 
Diversity encouraged by the world-wide selection of desirable genetics adapted to local conditions not only affected factors affecting time to maturity in corn, but also multiple metabolic and structural aspects of the species.  It is probable that size of vascular systems in stems, affecting movement of minerals and photosynthates, root structures and efficiency of absorption of individual minerals, number and reactivity of stomata, number and efficiency of chloroplasts and mitochondria must have been among the multiple inadvertent selections made by those early corn breeders as they selected for adaptation to their environments.  This variability is offered to current corn breeders as sources for continual adaptation to human needs.
 
A Germplasm Enhancement of Maize (GEM) project, a collaborative effort by USDA-ARS and public and private research scientists cross USA adapted maize germplasm with exotic germplasm in attempt to expand adaptation of traits selected under diverse environments.  These new combinations are intended to be sources of new gene combinations for future corn hybrids available to all potential corn growing environments. More information about GEM can be found at https://usda-gem.public.iastate.edu/GEM_Project/GEM_Project.htm