Date of Graduation

5-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Ehsan Shakiba

Committee Member

Leandro A. Mozzoni

Second Committee Member

Larry C. Purcell

Third Committee Member

Trenton L. Roberts

Fourth Committee Member

Fernando Grignola

Fifth Committee Member

Christopher G. Henry

Keywords

Breeding, Drought, Genetics, Irrigation, Protein, Soybean

Abstract

Soybean [Glycine max (L) Merr.], a legume species native to East Asia in the Fabaceae family, ranks among the most important food crops in the world. It is widely grown and known for its high protein and oil concentration. Soybean is valuable because its seeds have multiple applications in food, feed, pharmaceutical, and industrial enterprises. Even though seed yield is the most important trait, breeders have recently given a significant attention to quality traits, such as high protein or modified oil concentration. Soybean seed protein inheritance has been extensively studied; however, genetics of high-protein ‘BARC-7’ soybean are still unknown.On the other hand, soybean production in the United States Mid-South relies heavily on irrigation with 85% of soybean surfaces are supplemented with water in Arkansas. The most common irrigation practice in the U.S. Mid-South is furrow irrigation. Furrow irrigation could add an extra dimension of variation because of water gradients on the front and back of field, and potentially unequal flows between rows. However, the National Centers for Environmental Information reported a water shortage in eastern Arkansas, causing a reduction in water levels at irrigation reservoirs and generating concern on water availability for crop irrigation during reproductive stages. A reduction in groundwater availability could result in farmers having to skip or delay irrigation at a certain reproductive stage. Reduction in irrigation due to water quantity restrictions will significantly affect soybean yield, making variety selection increasingly important. Also, exploring molecular approaches to increase yield genetic gain has been one of the main challenges for soybean breeders and geneticists. Therefore, the objectives of this study were 1) to map of high-protein ‘BARC-7’ gene using F2-derived lines 2) to assess if irrigation onsets at different reproductive stages affect wilting, seed yield and key agronomic traits on determinate maturity group 5 (MG 5) soybean 3) to conduct a nested association mapping (NAM) for wilting, maturity, and seed yield and to identify superior individuals in seed yield using genomic approach under different irrigation onsets 4) to evaluate the spatial variability of furrow-irrigated soybean for seed yield, wilting, and maturity under four different irrigation onsets. Results suggested that QTL for protein and oil inherited from ‘BARC-7’ were identified on chromosomes 6, 13, and 20. The known major QTL on chromosome 20 was not detected. Results also indicated significant differences in wilting and yield but no significant differences in maturity, protein, oil content, and 100-seed weight across different irrigation onsets. Results revealed that a total of 4, 39, and 7 SNPs were found to be significantly associated with canopy wilting, maturity, and seed yield, respectively, using the combined data under different irrigation onsets obtained over four environments (location-year combination). Overall genomic selection accuracy was moderate ranging from 0.39 to 0.44, and genomic selection was efficient to select superior soybean lines under reduced irrigation. The spatial models displayed better data fitting (lower AIC and/or BIC) than the block model in each different irrigation level across different environments and traits. Indeed, genotype ranking for seed yield was different between the block model and the best spatial model, suggesting that spatial adjustment may be necessary for soybean breeding operations under furrow irrigation. Further validation in a breeding yield trial demonstrated similar results of the effectiveness in terms of AIC and/or BIC of the spatial model compared to the block model for soybean seed yield. The results from this study could contribute to proceed to a fine-mapping to the regions associated with high protein and oil in ‘BARC-7’ genetic background, to better understand mild drought on populations in order to define the breeding objectives and subsequent deployment of soybean lines under limited irrigation, and to suggest a spatial adjustment for soybean breeding operations under furrow irrigation.

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