Date of Graduation

8-2013

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Food Science

Advisor

Larry C. Purcell

Committee Member

Pengyin Chen

Second Committee Member

Trent Roberts

Third Committee Member

Rom Curt

Abstract

In soybean, nitrogen fixation is more sensitive to drought than other physiological processes like photosynthesis. The sensitivity of nitrogen fixation to drought has been associated with high shoot concentrations of ureide and nitrogen under well-watered conditions. Previous research by Hwang et al. (2013) detected quantitative trait loci (QTLs) in a KS4895 by Jackson population associated with shoot ureide and nitrogen concentrations. The present research evaluated the use of these QTLs in selecting genotypes with drought tolerant nitrogen fixation. Our objectives were to compare actual versus expected phenotype of recombinant inbreed lines (RILs) selected using molecular markers, and to evaluate the effects of shoot nitrogen and ureide concentrations on nitrogen fixation and yield under well-watered and drought conditions. We also evaluated differences in ureide concentration in four near-isogenic line sets that were developed based upon preliminary QTL data for ureide concentration. Isolines did not differ in ureide concentration, and subsequently we determined that preliminary QTLs were not associated with shoot ureide concentration. In 2011, field experiments were conducted in Fayetteville using 12 RILs selected using preliminary QTLs. Selection based on preliminary QTL information did not result in the expected phenotypes for ureide and nitrogen concentrations. Under severe drought conditions, however, RILs with low well-watered ureide and nitrogen concentrations had an increase in growth rate, nitrogen fixation rate, and yield (r2>0.50, P<0.001). In Fayetteville and Keiser 2012 field experiments, RILs were selected using QTL detected by Hwang et al. (2013). Selection resulted in the expected phenotypes for ureide and nitrogen concentrations. Under well watered conditions, genotypes with alleles for high ureide and nitrogen concentrations showed higher nitrogen fixation rates, higher percentages of nitrogen derived from the atmosphere and higher yields than genotypes with alleles for low ureide and nitrogen concentrations (r2>0.20, P<0.0001). Since nitrogen concentration may be positively correlated with yield under well watered conditions, genotypes with high yield and low shoot ureide and nitrogen concentrations need to be identified. The QTLs detected by Hwang et al. (2013) are an important tool for identifying these genotypes.

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