Date of Graduation

5-2021

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Leandro Mozzoni

Committee Member

Ehsan Shakiba

Second Committee Member

John Rupe

Third Committee Member

Lisa Wood

Keywords

flood tolerance, genomic selection, marker-assisted selection, soybean

Abstract

Waterlogging can be detrimental to soybean [Glycine max (L.) Merr.] growth and development, with effects ranging from chlorosis and stunting to yield loss and plant death. Soybean responses to, and the effects of, waterlogging are dependent on the growth stage of the plant at the initiation of waterlogging. The objectives of this study were: (1) to assess the effectiveness of Genomic Selection (GS), Marker Assisted Selection (MAS) and Phenotypic Selection for flood tolerance at the progeny row stage as compared to random selection, for the development of high-yielding flood-tolerant lines; and (2) to compare field-screening and hydroponic greenhouse screening methodologies for hypoxia tolerance. For the first objective, 391 individuals from four populations at the F4:5 generation were either: 1) screened for waterlogging tolerance at the R1 growth stage in observation or first-year yield trial stages; 2) subjected to genomic selection using two different training approaches; 3) underwent marker-assisted selection; or 4) were advanced purely based on agronomic adaptation under non-flooded condition. Subsequently, the tagged selections together with the base populations (control) were entered in a multi-location trial where flood tolerance and yield were assessed, and the responses were compared across the different selection methods. Results from this experiment indicated significant differences between visual selection and the base population, and between genomic selection and base population when long-rows experiment was used in the training set. Random selection and base population were also significantly different on the identification of flood tolerant lines, assessed as tolerance index and probability of discard. Random selection method resulted in the lowest tolerance index and highest probability of discard. We also observed that visual or genomic selection derived from hill plots did not outperform the control in terms of flood tolerance. In addition, all six methods and base populations had similar performance in terms of mean yield. This suggests that breeders must focus on selecting for flood tolerance early in the breeding stages, without major risk of reducing yield potential. For the second objective of this study, a total of 17 soybean genotypes were screened for waterlogging tolerance at the V2 growth stage and under a hydroponic system. Plots of responses by cultivar and test method were analyzed. We observed consistency in results between field and hydroponic system for most of the cultivars, enabling us to discard based on flood susceptibility. Identification of the most efficient selection method for flood tolerance, and the development of a greenhouse screening methodology, will aid plant breeders in developing new flood-tolerant cultivars.

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