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Association mapping is a powerful strategy for identifying genes underlying quantitative traits in plants. We have assembled and characterized genetic and phenotypic diversity of a sorghum [Sorghum bicolor (L.) Moench] panel suitable for association mapping, comprised of 377 accessions representing all major cultivated races (tropical lines from diverse geographic and climatic regions), and important U.S. breeding lines and their progenitors. Accessions were phenotyped for eight traits, and levels of population structure and familial relatedness were assessed with 47 simple sequence repeat (SSR) loci. The panel exhibited substantial morphological variation and little genotypic differentiation was observed between the converted tropical and breeding lines. The phenotypic and genotypic data were used to evaluate the performance of several association models in controlling for spurious associations. Our analysis indicated that association models that accounted for both population structure and kinship performed better than those that did not. In addition, we found that the optimal number of subpopulations used to correct for population structure was trait dependent. Although augmentation of the genotypic data with additional SSR loci may be necessary, the association models, genotypic data, and germplasm panel described here provide a starting point for sorghum researchers to begin association studies of traits and markers or candidate genes of interest. [ABSTRACT FROM AUTHOR]

The genetic structures of the Iowa Corn Borer Synthetic #1 (CB) and Iowa Stiff Stalk Synthetic (SS) maize (Zea mays L.) populations are important because these populations serve as the model for development of modern commercial hybrids. In 1949, CB and SS were used to start a reciprocal recurrent selection (RRS) breeding program at Iowa State University. This study was conducted to analyze more thoroughly the genetic diversity within this RRS program and illustrate how the RRS program has changed over time at the molecular level. The progress of this program was measured by analyzing the variation at 86 SSR loci among 28 progenitor lines and 30 plants sampled from each of seven cycles (Cycle 0, Cycle 1, Cycle 3, Cycle 6, Cycle 9, Cycle 12, and Cycle 15) in each population. The progenitors of these populations show a high amount of variation on the basis of expected heterozygosity (0.557). As the RRS program proceeded, this variation decreased (Cycle 15, 0.245). In total, a larger amount of genetic variation was found among plants within cycles (66%) than among cycles (13%) or between populations (21%). The repartitioning of variation from within populations (96% in progenitors) to between populations (58% in Cycle 15) over time is consistent with theoretical expectations of divergence between the populations. By sampling intermediate time points, we gained a comprehensive genetic view of CB and SS permitting evaluation of the molecular-level changes occurring as a result of reciprocal recurrent selection. [ABSTRACT FROM AUTHOR]

Examines the role of inbred lines in maize in the U.S. Genetic diversity of Zea mays; Use of molecular variance of gene frequencies in determining maize lines; Sources of inbred lines.