Corn Inbreeding

​Before intentional production of hybrid corn seed, corn growers selected varieties of seed best suited for growth in their environment and grain use. Leaf disease resistance was a more important character in the southeast United State, whereas ability to silk when under dry conditions became more significant in the western areas of the central USA. Other regional environment differences resulted in selection of different genetics in corn varieties.
 
This tendency for corn growers to select seed that best met their desired characteristics led to distinct regional varieties but also inadvertently led to some homozygosity of some negative genes.  This was happening worldwide as corn was distributed and then locally selected annually for desired characteristics.  As seed was selected locally and annually, the desired characters were expressed, and genetics affecting those characteristics became ‘fixed’, inbreeding caused homozygosity of not only the desired genes but also of some other genes.  That affect ultimately limited the total grain production of the saved seed variety.
 
Occasional experiences of mixing of races showed the extra vigor the yield repression when ‘races’ of corn were crossed. It is written that an Ohio corn grower accustomed to planting a southern dent variety supplemented the poor emergences in his field with planting a northern flint corn in the gaps of the field. He saved seed from that field after harvest, as usual, for the next season.  That seed resulted in a largest grain yield, the plants having the advantage of the dominant genes of one variety overcoming the recessive negative genes of the other variety.
 
This phenomenon was commonly noted by professional corn breeders as understanding of corn genetics became better understood.  Vigor repression in corn was clearly linked to inbreeding and restoration of vigor was understood to occur when some varieties were crossed. Inbreeding was needed to get expression of some characteristics but also led to homozygosity of some negative recessive genes. If crossed with the certain other varieties that had dominant forms of those genes, the resulting progeny did not express the negative characters.  This attracted the attention of academic and commercial people in the early 1900’s as they began to experiment with the practicality of corn hybrids.