Geographical distribution and diversity of maize (Zea mays L. subsp mays) races in Mexico

The center of origin of maize is in Mexico and maize diversity is very high in many parts of the country. Here we describe and analyze the geographic distribution and diversity of maize using a database of 18,176 georeferenced observations of maize races. The number of observations by race follows the common "hollow curve" distribution, with six races comprising 54 % of the records and 37 races only 10 %. Few races are widespread, and some have a highly localized distribution. The average maximum distance (D (max)) between two records of the same race was 1169 km, but seven races had a D (max) lower than 200 km. The average circular area range size (CA(25)) was 51, but 14 races had a CA(25) lower than 10. Some races have very few observations but were found over a large area. These races may not be valid and their classification should be reviewed. Areas of high race richness and diversity are in mountainous northwest, south central, and southern Mexico in the states of Oaxaca, Jalisco, Michoacan and Chiapas. Six contiguous maize regions were defined using hierarchical clustering. Despite the high sample size, further sampling could improve estimates of race diversity in several regions.