The Genomic Tree of Mexican Maize (Zea mays L.)

Diversity of Mexican maize was first described by Wellhausen et al. (1952), who proposed that Mexican maize consisted of 25 well defined races belonging to one of the following groups:  Ancient Indigenous, Prehistoric Mestizos, Pre-Columbian Exotic, and Modern Incipient. After the proposal of Wellhausen et al. (1952), 34 new Mexican maize races have been described up to date. Several morphological studies have confirmed the genetic relationships of the 25 races described by Wellhausen et al. (1952), and have included in the tree most of the new Mexican races. Molecular analyses have showed that Prestoric Mestizos races were developed from the hybridization of the Ancient Indigenous races and the Pre-Columbian Exotic races, as proposed by Wellhausen et al. (1952). However, the genomic tree based entirely on molecular data has not been obtained yet.

In the present research we study the genetic relationships of the 59 Mexican maize races with SSRs. We sampled accessions representative of each race. Twenty plants of each accession were planted and leaf tissue was bulked for DNA extraction. Each accession was represented by a bulk of leaf tissue. The DNA of bulks will be genotyped with 30 SSRs using gel electrophoresis analysis. Only presence or absence of SSR alleles in bulks will be scored to calculate similarity measures and the dendrogram. This research is supported by a grant from the SEP-CONACYT, Mexico. We will show in this paper, the origin and perspective of the discrete allele uniform distribution as the base distribution to obtain a genomic tree.