History of corn’s origin in tropical environments to its spread around the earth is fascinating to me. Not only did the people in Mexico select mutants that held onto the seed instead of instantly shattering and scattering seed before harvest, but they also found mutants in the Teosinte plants that stored more starch in endosperm. As people migrated through that part of Mexico carrying the seed to their environments. They identified and selected mutants that allowed reproduction in the new locations.
Among the most significant is adaptation the reduced length of growing season in the temperate zones of earth. Tropical corn, such as those originally in Mexico, flowered when day light time was reduced, the daylength sensitivity that affects many flowering species. Those short days occur too late in tropical corns life, resulting in tropical corn in temperate zones to not complete filling of grain before frost. Adaptation to temperate zones require emphasis on accumulation of heat to trigger the change of the apical meristem from producing more leaves to production of flowers.
One study that I did many years ago compared the heat units to time of apical meristem showing a tassel to the maturity rating for many commercial hybrids. Timing of that differentiation, occurring in June correlated very closely with our final maturity ratings for those hybrids. This supported the hypothesis that it is the heat units beginning immediately after planting that is most significant in determining the maturity of a corn crop. Heat after switching the growing points from producing stem and leaf tissue to tassel and ear tissue has an influence, but the earlier season affect is greater. Maturity in most corn belt corn is controlled by several genes affecting response to accumulating heat soon after planting. Tropical corns are also influenced by heat but other genes affecting response to number of hours of continuous darkness have a greater effect on time to flowering.
As our climate changes the genetic diversity available to us will allow further adaptations in corn.
The changing environments and dynamics of genetics allows and demands a continual need for diversity in corn and, actually, all other aspects of life, including humans. There is no reason to think these dynamics will end. Genetic mutations allowed the origin of Homo sapiens and its adaptation to many environments including those caused by pathogens. Genetic mutations allowed the origin of corn from a weedy grass species in central Mexico and further adaptations to grain production around the earth. Natural mutations in this annual plant species and slight changes in the DNA code frequently has no recognizable affect but some provides the needed resistance to a future pathogen, perhaps also undergoing mutations.
Efforts of corn breeding programs to continually select the best genotypes for today’s environments, as well as those by corn growers to provide good environments will be critical each year. This requires continual effort to select those best genetics for the time and place. We celebrate diversity in corn and humans.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.