Tracing the Genomic Tree of Mexican Maize (Zea mays L.) By Analyzing DNA Pools.

Diversity of Mexican maize was first described by Wellhausen et al. (1952), who proposed that Mexican maize consisted of 25 well defined races. After the proposal of Wellhausen et al. (1952), 34 new Mexican maize races have been described up to date. Molecular analysis has been extensively used to study the molecular diversity and genetic relationships of maize races; nevertheless, the molecular tree of the Mexican maize has not been obtained yet.   

In the present research, we study the genetic relationships of 58 Mexican maize races with the analysis of SSRs. Seeds of representative accessions of each race were grown in the greenhouse and harvested individually. Bulks of leaf tissue of 20 plants of each accession were obtained for DNA extraction. The bulks are being genotyped with SSRs using acrylamide gel electrophoresis analysis. Allele frequencies in bulks are not determined, instead, only presence or absence of amplified bands in bulks is scored. The genomic pools of the different races are obtained from the DNA fingerprints of the representative accessions, and they are the basis to estimate a genomic tree. We will show in this paper the theoretical advantage of using presence-absence scores over the allele frequency data to calculate a distance matrix. We also show how genomic pools are formed, and some results of the analysis of the 25 Mexican races described by Wellhausen et al. (1952). This research is supported by a grant from the SEP-CONACYT, Mexico.