Corn’s unique biology and history contributes to the crop’s worldwide distribution and productivity today. About 8-10000 years ago, probably in the Balsas River valley of Mexico, someone or perhaps several people, found a mutant teosinte plant in which the hard fruit casing did not extend fully around the enclosed single seeded grain, the kernel. Someone realized that this made the kernel very edible and consequently propagated some of the seed. It was recently discovered that a single mutation in the TGA1 gene in Teosinte, changed a single nucleotide in the DNA code of this gene. This resulted in an amino acid change (asparagine instead of lysine) component of a protein critical to the development of the seed case in Teosinte and corn. Not only were the starch components of the seed more easily extracted by humans, but removal of the hard case allowed for greater growth of the kernels. This was only one of several mutations that ultimately resulted in we know as maize but we are appreciative that people a very long time ago, recognized the advantage of this mutation. A description of the mutation is in http://phys.org/news/2015-07-tiny-genetic-tweak-corn-kernels.html.
Other mutations assisted humans as they moved from a plant with about 20 seeds per ‘ear’ encased in a hard covering, into a plant that were easily used for food. It is notable that the initial mutation was to an annual plant version of Teosinte, thus allowing for selection of new genetics each year. A thousand years could equal 40-50 generations of humans but is 1000 generations of corn, allowing a lot of opportunity for genetic changes as humans made selections for adaptation to the environments and their food.
There is archeological data supporting that the early corn, although originating in a valley in south central Mexico, was moved to the highlands of Mexico.
The first European exposure to corn was about 500 years ago. Europeans called it corn because that was the common name for other grains. Seed was moved to Europe where it spread from even further to Africa and Asia, again with locals selecting for adaptation to their conditions. This included a wide range of required time from planting to harvest, disease pressure and local food uses.
Within the USA, corn that moved through the Southwest and then north and east tended to be flint types whereas the Southeast corn was floury types perhaps with genetics influenced by Caribbean corn migration. Flint corns in the Northeast USA tended to have fewer kernel rows than the semi-dent types of the southeast. As people became more stationary, with each farmer having the opportunity to saved seed that favored their environment, food and livestock needs, multiple uniquely genetic varieties developed across the continent. Although local selections were based upon gross performance, ultimately selections were having effects on root structures, photosynthesis parameters, moisture stress tolerance, germination in cool soils, and disease resistance. Separation of the male and female flowers of corn became a major asset to avoid complete inbreeding as farmers kept desirable ears to save for the next season. Most pollen from an individual corn plant does not fall on its own silk, almost guaranteeing cross pollination in open fields. Until 80 years ago, open pollinated varieties were the sources of corn, with yields in the USA usually less than 30 bushels per acre.
Those corn breeders contributed to the wide genetic diversity for current corn breeders to tap into for the latest traits needed for successful crops.
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.