Degree Type

Dissertation

Date of Award

2003

Degree Name

Doctor of Philosophy

Department

Agronomy

First Advisor

E. Charles Brummer

Abstract

As part of an ongoing effort to implement a semi-hybrid breeding scheme Medicago sativa subsp. falcata genotypes from across the subspecies range were testcrossed to elite subsp. sativa populations to determine hybrid performance. The goal was to determine, which falcata germplasm created the most superior hybrids. Factors such as falcata parental morphology, molecular fragment differences, and climate of origin variables were used to group the falcata genotypes. European falcata germplasm displayed superior biomass yield and heterosis compared to Asian falcata germplasm. The superior European performance was likely due to genetic differentiation between European and Asian material. In addition climate of origin variable selection on parental falcata genotypes caused genotypes from climates with low June photosynthetically active radiation to create better yielding and more heterotic sativa-falcata hybrids. Improved morphology was not correlated with heterosis, but was correlated with improved biomass yield. However, it was observed that visually pre-selected genotypes for autumn vigor had increased biomass yield and heterosis performance when compared with randomly chosen genotypes from the same population. Falcata morphological variation overlapped elite-sativa variation for most morphological traits. However, for regrowth in particular no falcata populations were found that came anywhere near sativa regrowth, suggesting the need for intense selection for this trait. Despite slower regrowth, after first and second harvest, average sativa-falcata hybrids performance, by 30 days post-harvest, had reached the expected mid-point between their parental subspecies means after which time they showed increasingly outperformed the mid-parental subspecies mean. Based on this study focused falcata germplasm selection for testcrossing can be implemented.*;*This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.

DOI

https://doi.org/10.31274/rtd-180813-11475

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu

Copyright Owner

Heathcliffe Riday

Language

en

Proquest ID

AAI3085885

File Format

application/pdf

File Size

151 pages

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