University of Hohenheim

About: University of Hohenheim is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Population & Soil water. The organization has 8585 authors who have published 16406 publications receiving 567377 citations.

Selection theory for marker-assisted backcrossing.

Abstract: Marker-assisted backcrossing is routinely applied in breeding programs for gene introgression. While selection theory is the most important tool for the design of breeding programs for improvement of quantitative characters, no general selection theory is available for marker-assisted backcrossing. In this treatise, we develop a theory for marker-assisted selection for the proportion of the genome originating from the recurrent parent in a backcross program, carried out after preselection for the target gene(s). Our objectives were to (i) predict response to selection and (ii) give criteria for selecting the most promising backcross individuals for further backcrossing or selfing. Prediction of response to selection is based on the marker linkage map and the marker genotype of the parent(s) of the backcross population. In comparison to standard normal distribution selection theory, the main advantage of our approach is that it considers the reduction of the variance in the donor genome proportion due to selection. The developed selection criteria take into account the marker genotype of the candidates and consider whether these will be used for selfing or backcrossing. Prediction of response to selection is illustrated for model genomes of maize and sugar beet. Selection of promising individuals is illustrated with experimental data from sugar beet. The presented approach can assist geneticists and breeders in the efficient design of gene introgression programs.

SSR and Pedigree Analyses of Genetic Diversity among CIMMYT Wheat Lines Targeted to Different Megaenvironments

Abstract: Improved bread wheat (Triticum aestivum L.) cultivars for diverse agroecological environments are important for success in the effort to increase food production. In the 1980s, CIMMYT introduced the megaenvironment (ME) concept to breed wheats specifically adapted to different areas. Our objective was to analyze the genetic diversity among 68 advanced CIMMYT wheat lines targeted to different MEs by using 99 simple sequence repeats (SSRs) and the coefficient of parentage (COP). The average number of alleles detected was higher for the 47 genomic SSRs (5.4) than for the 52 SSRs derived from expressed sequence tags (EST) (3.3), but gene diversity between MEs was similar for both types of markers. No significant differences among the five MEs were observed for the means of SSR-based genetic similarities (GS), calculated as 1 − Rogers' distance, and COP values. Both measures showed a low correlation (r = 0.43). High levels of genetic diversity were found within the germplasm targeted to each ME. However, principle coordinate analysis based on modified Rogers' distances did not separate the genotypes according to their targeted MEs. We conclude that presence of a single core germplasm can reflect large phenotypic differences. A sufficient number of diverse breeding lines for each ME is required because MEs generally combine various production areas. SSRs represent a powerful tool to quantify genetic diversity in wheat, but genotypic differentiation for adaptation to specific MEs in the CIMMYT program could not be proven.