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/Mentor

Purcell, Larry C.

Committee Member

Chen, Pengyin

Second Committee Member

Roberts, Trenton L.

Third Committee Member

Rom, Curt R.

Keywords

Biological sciences; Drought; Drought tolerance; Nitrogen fixation; Soybean

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, P0.20, P

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