Isozymatic diversity in the races of maize of the Americas

To determine the genetic diversity of the races of maize of the Americas, 1 080 accessions representing more than 300 races were analyzed for 13 enzyme systems encoded by 23 genetic loci. The analysis of the data revealed very different levels of genetic diversity across countries. A total of 329 :al leles were recorded; however, about 81% of the alleles found in the :access ions studied were rare, occurring at frequencies below 0.01; some were obse rved in only one accession or only one race. There are two geographical reg ions where allelic diversity is concentrated: Mesoamerica and the Andean Re gion. In general, the levels of racial diversity can be attributed to geo g raphic range. The uses by human groups and sample sizes of the seed lots us ed by farmers from one cycle to the next are factors which likely affect th is diversity.