Zea mays L., corn, is a species of the Maydae tribe, included in the subfamily Panicoidae, family Graminea (Poacea). Genera belonging to the Maydae tribe  include Zea and Tripsacum in the Western Hemisphere.  Corn is a separate species within the Zea subgenus, with a chromosome number 2n = 20,21,22,24(9). The wild  species closest to corn  is teosinte, found in Mexico and  some other places of Central America, where it may cross with cultivated corn in production fields. Cultivated corn may also cross with a more  distant genus, the  Tripsacum.  The crossing seldom happens and results in a sterile male progeny.
Corn has  a history of eight  thousand  years in the Americas. Out of all cultivated plants, corn is probably the  one possessing the largest genetic variability.  Today, about three hundred races of corn are identified and, within each such race, there are thousands of cultivars. Corn is currently the cultivated species that reached the highest degree of domestication and it may only survive in nature when raised by man(4). Normally, the maintenance of  this genetic variability has been achieved through individualized storage, in germplasm banks, under  controlled humidity and temperature. There are several germplasm banks,  in Brazil and all over the world. Embrapa, the Brazilian Agricultural Research Agency, has two germplasm banks,  one at Embrapa Recursos Genéticos e Biotecnologia, Embrapa Genetic Resources and Biotechnology, in Brasília, Federal District, Brazil, and another  at Embrapa Milho e Sorgo, Embrapa Maize and Sorghum, in Sete Lagoas, Brazil. Corn is farmed in over 100 countries, with a total estimated production of 705  million tons per year.
Corn is one of the most important food  sources in the world and  is the raw material  for a large range  of products. From 70% to 80% of corn produced in Brazil is consumed by the swine and poultry productive chain.
Brazil is the world third largest corn producer, with  an output of about 35 million tons  in 2005, behind the United States of America (282 million tons) and China (139 million tons)(11).In Brazil, corn is planted basically in two different crops (summer and safrinha, or  small  crop) and is cultivated in practically all the domestic territory, with 92% concentrated in the Southern Region (47% of production), Southeastern Region (21% of production) and Center Western Region (24% of production)(8).