Mitochondrial DNA variation in races of maize indigenous to Mexico.

Mitochondrial DNAs have been examined in accessions of 25 Mexican races of maize and compared with the mitochondrial DNAs previously found in inbred lines from the USA. Many variants were found. Low molecular weight DNA components, not previously found in US lines, were found in many of the accessions. Accessions classified as belonging to the same race, and plants from a single accession, sometimes had different mitochondrial genomes. Mitochondrial genomes similar to those in T and S cytoplasms were found in Mexican accessions.A low molecular weight linear DNA species has partial homology with a sequence in the high molecular weight mitochondrial genome. All plants with a shorter version of the linear molecule had a correspondingly altered region of homology in the high molecular weight genome.There is evidence that the geographical distribution of mitochondrial DNA types within Mexico is not random. One type, found in the oldest races, appears to be widely dispersed but another less common type appears to be confined largely to coastal regions. The potential value of these findings in maize breeding and for evolutionary studies is discussed.