Date of Award
Doctor of Philosophy
Zoology and Genetics
Randy C. Shoemaker
The purpose of this dissertation was to retrospectively analyze the process of soybean cultivar development from a molecular perspective, by following the inheritance of RFLP markers in a pedigree analysis. Five methods of analysis are included in this dissertation;Sixty-four plant introductions, cultivars, and breeding lines were analyzed to define a core set of 97 probes with a high likelihood of detecting a polymorphism in elite germplasm. The ability to trace regions of chromosomes from parent to offspring and the application of pedigree-based mapping was demonstrated, which is the cosegregation of phenotypic traits and RFLP markers based on pedigree information. Three qualitative traits were associated with molecular markers;The second analysis evaluated recombination events which occurred during cultivar development. Twenty-six cultivars were analyzed at 89 RFLP loci. Between one and eleven recombination events were detected per cultivar. Large linkage blocks, inherited intact, were identified, as well as recombination "hot-spots";The third analysis compared values of genetic relatedness based on RFLP markers with values based on coefficient of parentage, metric measurements, and isozyme patterns. RFLP similarity values were most similar to coefficient of parentage values, and least similar to values derived by measuring metric characters;In the fourth analysis, RFLP allele frequencies were calculated for each generation of cultivar development and each maturity group. Regression analysis identified six and ten loci with linear trends among generations and maturity groups, respectively. The observed loss of genetic diversity after four generations of cultivar development was 10.6%. Previous literature reported a loss of 20%, based on coefficient of parentage values. Thus, the rate of genetic diversity loss observed was much slower than previously predicted;In the final analysis, 108 soybean lines, related to 18 ancestral "types", were evaluated at 50 RFLP loci to determine if early cultivar selections made from plant introductions were derived by mutation, outcrossing, accidental seed mixture, or a heterogeneous plant introduction. Mutation was not a primary factor in the derivation of selections from ancestral lines, and evidence of a heterogeneous seed mixture was seen in one ancestral line previously thought to be homogeneous.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Lisa Lou Lorenzen
Lorenzen, Lisa Lou, "Soybean cultivar development: a genome perspective " (1994). Retrospective Theses and Dissertations. 10626.