Understanding and effectively leveraging the genetic diversity present in breeding programs is decisive for increasing genetic gain and rapidly responding to changes in breeding objectives. In this work, a set of 472 representative lines from the Argentine National Institute of Agricultural Technology (INTA) temperate maize (Zea mays L.) breeding program was genotyped with a mid-density DArTag panel to assess genetic diversity, degree of linkage disequilibrium (LD) and population structure. In addition, a breeding core set that captured the program’s genetic diversity was selected to facilitate future functional studies. After curation of the genotypic matrix, 461 lines and 2,199 single nucleotide polymorphisms (SNPs) remained in the analysis. SNPs were highly informative, with an average polymorphic information content of 0.32. Inbred lines exhibited low heterozygosity (1.6

The maize inbred line B73 has been extensively studied at the molecular level. Researchers now have access to the genome sequence of B73 as well as to databases of biallelic and multiallelic markers where functional polymorphisms between B73 and a public inbred line population can be compared to relate genotypes to phenotypes. This indicates the importance to determine the genetic fidelity of the germplasm during preservation and propagation processes, in particular, when seeds of reference inbred lines such as B73 are maintained. The aim of this study was to assess the genetic uniformity among three different sources of the B73 inbred line by means of 75 Simple Sequence Repeats (SSRs). The three B73 sources showed homozygosis; however, some accessions differed greatly from the expected locus size predicted at the reference B73 genomic sequence. A particular haplotype was prevalent in the USDA accession PI550473. The error rate of the allele size determination was estimated. The genotyping technique used in this work allowed the separation of alleles of +/- 2 bp range difference within the same electrophoresis run, whereas allele size estimations between experiments, within the laboratory, differed in +/- 4 bp range difference. Besides experimental errors in genotyping, the putative cause of differences among accessions could be attributed to seed contamination and genetic drift. The B73 accessions evaluated in our work can be shared among laboratories to precise genotyping and phenotyping of maize inbred lines.

The genetic diversity of maize (Zea mays L) is a valuable and strategic natural resource that plays a key role in the breeding progress. However, exploitation of genetic variability from landraces has not reached a significant level of utilization in breeding programs in Argentina yet. In order to establish their breeding potential, the best 15 out of a group of about 300 landraces from Argentina, were evaluated for various agronomic characters in testcrosses with five lines representing different heterotic groups. Testcrosses were evaluated in nine environments during two growing seasons. A factorial array of those landraces and tester lines was used. Differences for landraces, testers, and landrace x tester interactions were detected for ear diameter and length, ear attachment and plant height, and grain yield. Yield data were further analyzed following additive main effects (landrace and tester) and multiplicative interaction (landrace x tester) models. The first two principal components were significant and accounted for 67% of that interaction. The first axis was consistent with the Argentine flint vs. US dent (Mo17), and US dent (B73) vs. US dent (Mo17) heterotic patterns. The second axis exhibited a contrast between Argentine flint and US dent (B73 or B73 derived line) heterotic groups. The first two principal components of the landrace x tester interaction and mean performance of testcrosses were considered to identify eight landraces as parents of three composite populations.