Degree Type


Date of Award


Degree Name

Master of Science



First Advisor

Walter R. Fehr


Glyphosate is a popular herbicide for weed control in fields planted to soybean [Glycine max (L.) Merr.] cultivars with a transgene that provides tolerance to the chemical. A transgenic event MON89788, known commercially as Roundup Ready 2 Yield y, was developed by the Monsanto Co. as an alternative to the event 40-3-2 for glyphosate tolerance in soybean. The objective of our study was to compare the agronomic and seed traits of glyphosate-tolerant (GT) lines and glyphosate-susceptible (GS) lines from populations segregating for MON89788. The transgene was backcrossed into three GS cultivars to develop BC2 populations. There were 27 GT and 27 GS BC2F2-derived lines from each backcross population evaluated at four Iowa environments in 2010. The means of the GT lines were not significantly different from the GS lines in any of the populations for seed yield, lodging score, and palmitate, oleate, and linoleate concentrations. The maximum significant difference between the means of the two types was 0.4 d for maturity date, 2 cm for plant height, 5 mg sd-1 for seed weight, and 2 g kg-1 for protein, 1 g kg-1 for oil, 1 g kg-1 for stearate, and 0.2 g kg-1 for linolenate concentrations. The significant differences among lines within each type and the overlap in their distributions for all of the traits indicated that it would be possible to select GT or GS lines with comparable performance from populations developed by crossing a GS parent to a GT parent with the MON89788 event.

Reduction of the palmitate concentration in soybean oil is desirable for reducing the amount of saturated fat in the human diet. Chemical mutagenesis was used to develop the line A22, with the mutant allele designated fap3(A22) that reduces palmitate concentration in the seed oil. The objective of our study was to determine the molecular basis of the fap3(A22) mutation and develop a corresponding molecular marker to assist in future efforts for developing soybean cultivars with low saturated fat. DNA sequence analysis of GmFATB1a, the major 16:0-ACP thioesterase gene of soybean, revealed a single nucleotide polymorphism (SNP) resulting in a nonconservative amino acid substitution that is likely to be detrimental to enzyme function. An association analysis was conducted using F2-derived lines from a cross between the cultivar Archer (Fap3Fap3) and A22 (fap3fap3) that had been analyzed for their palmitate concentration by gas chromatography. Molecular genotyping of these lines established a perfect correlation between lines phenotypically classified as homozygous for the Fap3 allele or homozygous for the fap3(A22) allele based on their palmitate concentration. The polymorphism in the GmFATB1a gene was used to develop a functional, co-dominant marker that could be used to distinguish the Fap3 and fap3(A22) alleles in segregating populations. This marker will be useful for breeders who are developing low-saturate cultivars with the fap3(A22) allele.

Copyright Owner

Brian De Vries



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143 pages