Principles of Plant Genetics and Breeding

Taxonomy
Kingdom Plantae
Subkingdom Tracheobionta
Superdivision Spermatophyta
Division Magnoliophyta
Class Lilliopsida
Subclass Commelinidae
Order Cyperales
Family Poaceae
Genus Zea L.
Species Zea mays L.
Economic importance
Corn or maize is the single most important crop in the
USA. It is grown on more than 20% of the cropland.
Most of the production occurs in the region of the US
called the Corn Belt where six states, Iowa, Illinois,
Nebraska, Minnesota, Indiana, and Ohio, account for
about 80% of national production. Corn is grown in
every state except Alaska. Iowa leads the nation with
22% of the total production. Corn is the fouth most
important crop in the world, behind wheat, rice, and
potato in total production. More than 327 million acres
of corn are planted each year, worldwide. World yields
average about 42 bushels per acre (see Appendix 2 for
conversion rates of units).
There are six “corn belts” in the world – the US
Corn Belt, Danube basin (southwest Germany), Po
valley (north Italy), plains of north China, northeast
Argentina, and southeast Brazil. On the world scene,
the USA, China, Brazil, Mexico, France, and Argentina
together account for 75% of the world’s corn production,
the US accounting for about 40% of this total.
Other producers include Romania and South Africa.
In 1866, the US Department of Agriculture (USDA)
28
Breeding corn
reported 30 million acres of corn were harvested at an
average yield of about 24 bushels/acre. In the early
1990s, about 100 million acres were grown, with an
average harvested yield of 28 bushels/acre. However, in
2000, USDA reported 67 million acres of harvested
corn with an average yield of 118 bushels/acre. The
dramatic increase in yield over the period is attributed to
the adoption of hybrid seed and the use of fertilizers.
Corn has the highest value of production of any crop
in the USA, averaging 8 billion bushels worth US$20
billion per year.
Origin and history
Corn is arguably the most completely domesticated of
field crops. Modern corn is incapable of existing as a
wild plant. No wild form of corn is known. Its origin is
probably Mexico, or Central America. It was produced
as early as 6000 bc in Tehuacan, Mexico by the Mayan
and Aztec Indian civilizations. It was taken north by
the native Americans. Corn was dispersed to the Old
World in the 16th and 17th centuries. The explorers
introduced Indian corn to Europe and Africa. Modern
varieties have larger cobs and a greater number and
weight of kernels per ear as compared to the original
Indian corn. The modern cultivated plant is believed to
have been obtained through the process of mutation,
coupled with natural selection, and mass selection by the
American Indians. It is proposed that corn’s progenitor
may be a domesticated version of teosinte, a wild grass
that occurs in Mexico and Guatemala.
Adaptation
Corn has a wide geographic adaptation. It is grown from
as far north as 58°N latitude to 35–45°N latitude. It is