The emergence of high-throughput, high-density genotyping methods combined with increasingly powerful computing systems has created opportunities to further discover and exploit the genes controlling agronomic performance in elite maize breeding populations. Understanding the genetic basis of population structure in an elite set of materials is an essential step in this genetic discovery process. This paper presents a genotype-based population analysis of all maize inbreds whose Plant Variety Protection certificates had expired as of the end of 2013 (283 inbreds) as well as 66 public founder inbreds. The results provide accurate population structure information and allow for important inferences in context of the historical development of North American elite commercial maize germplasm. Genotypic data was obtained via genotyping-by-sequencing on 349 inbreds. After filtering for missing data, 77,314 high-quality markers remained. The remaining missing data (average per individual was 6.22 percent) was fully imputed at an accuracy of 83 percent. Calculation of linkage disequilibrium revealed that the average r2 of 0.20 occurs at approximately 1.1 Kb. Results of population genetics analyses agree with previously published studies that divide North American maize germplasm into three heterotic groups: Stiff Stalk, Non-Stiff Stalk, and Iodent. Principal component analysis shows that population differentiation is indeed very complex and present at many levels, yet confirms that division into three main sub-groups is optimal for population description. Clustering based on Nei’s genetic distance provides an additional empirical representation of the three main heterotic groups. Overall fixation index (FST), indicating the degree of genetic divergence between the three main heterotic groups, was 0.1361. Understanding the genetic relationships and population differentiation of elite germplasm may help breeders to maintain and potentially increase the rate of genetic gain, resulting in higher overall agronomic performance.

Maize (Zea mays, L.) breeding research in the public sector involves identifying novel genes, alleles, and breeding procedures that have promising commercial applications, but this role is stymied due to limited access to commercial quality lines and hybrids. Use of lines recently released from Plant Variety Protection (PVP) may be a solution. Our overall goal was to investigate the extent and nature of the allelic diversity in elite maize germplasm at the molecular level and gain insight into how this allelic diversity relates to the performance of superior hybrids. The specific objectives were to (i) characterize the genetic composition of 12 selected elite inbreds, (ii) evaluate these inbreds and their 66 F1 hybrids and segregating F1 derived F2 populations for an extensive number of leaf, tassel, and ear traits, including yield, and (iii) perform a statistical and quantitative genetic analysis to identify significant genetic variation thereof. Cluster analysis based on pedigree relationships and molecular markers indicated that the selected elite inbred parents are genetically diverse. Applying the Eberhart and Gardner general model we confirmed the presence of substantial additive, dominance, and epistatic variation in the elite germplasm selected and developed for this experiment. Experimental material derived from Ex‐PVP lines will be an important component of maize breeding research on increased productivity. In this research, hybrid mapping populations will prove to be invaluable for detection of nonadditive quantitative trait loci and association effects in yield related traits.

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In 1994-95, sources of heat tolerance were identified in common beans after screened several germplasm and advanced lines nurseries in Choluteca and Nacaome (≤ 50 masl), in the southern region of Honduras. The best heat tolerant genotypes were validated under greenhouse controlled conditions (35/27 °C day/night) in Geneva, New York. Afterward, crosses were made to develop small-red bean lines with heat tolerance and resistance to BGMV and other limiting factors. The F2- F5 segregant populations were evaluated for multiple traits including BGMV, common bacterial blight, angular leaf spot, rust, low fertility conditions, and selected for agronomic performance and commercial value. In 1998, 217 F6 and F7 advanced lines were evaluated in the irrigation district Lempa-Acahuapa (20 masl), in the Pacific region of El Salvador for heat tolerance and BGMV. The same nurseries were evaluated in Liberia, in the Northwest region of Costa Rica, for tolerance to high temperatures; and at Zamorano, Honduras for resistance to common bacterial blight, angular leaf spot and rust. A group of lines were identified having superior yield and adaptation than commercial checks, under high temperature conditions in El Salvador and Costa Rica. Some of these lines were also resistant to BGMV in El Salvador, and moderate resistant to web blight in Costa Rica, and they had excellent agronomic performance and good commercial value.