Date of Graduation

12-2016

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Pengyin Chen

Committee Member

Larry C. Purcell

Second Committee Member

Richard E. Mason

Third Committee Member

John Rupe

Fourth Committee Member

David M. Miller

Abstract

Drought causes significant yield reductions in soybean. The development of drought-tolerant cultivars is an effective alternative to overcome this abiotic stress. Slow wilting, prolonged nitrogen fixation, and minimal yield reduction under water stress play an important role in evaluating breeding materials. Despite advances in knowledge about plant responses to drought conditions, there is little information on effective methodologies for phenotype screening in the field, and some QTLs have been identified for drought tolerance. Field screenings under drought and irrigated conditions are necessary to detect drought tolerant lines. In addition, QTLs and molecular makers associated with drought tolerance traits will greatly facilitate the development of tolerant lines through marker-assisted selection (MAS). The objectives of this study were: 1) to evaluate whether selection of high-yielding lines under irrigation in the preliminary stage is a positive predictor of the performance of these lines under drought conditions, and 2) to identify/confirm QTL’s associated with slow wilting and nitrogen fixation for drought tolerance. For the first objective, yield performances of 87 genotypes derived from three different populations were evaluated under rain-fed conditions versus standard irrigation. The second objective was to identify QTLs associated with slow wilting, shoot ureides and nitrogen concentrations in soybeans. For this objective, 148 lines from an F4-derived population (R07-7044 x R01-581) were screened with SNP markers and molecular analysis was conducted. Results for the first project showed four different types of yield performance on the lines. The high-yielding lines under full irrigation also had high yields under drought indicating that the selection of high-yielding lines in initial stages under irrigation is a good indicator of the profitable yielding lines under moderate drought conditions. In the second project, results showed two new QTLs for shoot nitrogen on chromosomes 6 and 11, and confirmed two shoot ureide QTLs on chromosomes 10 and 13. Four new QTLs for wilting were identified on chromosomes 11, 13, 14, and 18. These newly confirmed QTLs and molecular markers will be useful for marker-assisted selection for drought tolerance improvement in a soybean breeding program.

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