Corn inbreeding

​As it became apparent to some corn breeders in the early 1900’s that consistency and repeatability of genetics in corn required creating homozygous inbreds from populations frequently expressing heterosis.  The enigma was that inbreeding greatly reduced the volume of hybrid seed to be planted but the production of grain from those hybrid seed was greater than produced by indigenous varieties.  A few academic corn breeders pushed the idea of using the hybrids as parent seed to make double cross hybrids to overcome the seed volume problem.  They encouraged several farmer seed producers to adapt this concept in the 1930s.  The significance of heterosis resulting from crossing specific inbreds became obvious to many during the 30’s, stimulating investigation into the genetics and botany of corn in academia and entrepreneurship among farmer breeders.  
 
As more farmers switched to using hybrid seed, public and private corn breeders increased inbred breeding programs.  New synthetic populations were created by breeders by crossing seed from existing varieties, selecting for heterosis by crossing with opposing inbreds, recycling the best, testing again and repeating the cycle to create new improved populations from which new inbreds could be created.  Stiff stalk synthetic population created at Iowa State University became and continues to be a powerful source of new inbreds that commonly used as female parents of hybrids.  Populations derived from varieties with origin in Eastern USA and grossly identified as Lancaster often became sources of inbreds expressing heterosis with stiff stalk derived inbreds.  
 
Breeding efforts to select more productive seed parents, improved seed production methods and economics of corn grain led to the introduction of single cross hybrids in the USA in the late 1960s.  A similar pattern developed in the multiple environments on other continents as well.  Continual selection by humans from the diverse genetics selected by previous human generations has led to continual improvement of grain productivity of this species. Its biological features of separation of male and female flowers, C4 photosynthesis, easily transported seed and 30-40000 genes has served us well.