Date of Award

5-2012

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant Sciences

Major Professor

Vincent R. Pantalone

Committee Members

Dean A. Kopsell, Carl E. Sams, Dennis R. West

Abstract

Soybean [Glycine max (L.) Merrill] is an important crop throughout the world. Among the many seed quality traits contained in soybean are isoflavones, which are associated with numerous health benefits, including cancer prevention, improved cardiovascular health, improved bone health, and reduced menopausal symptoms. This study sought to identify quantitative trait loci (QTL) controlling soybean isoflavones genistein, daidzein, glycitein, and total isoflavone content to gain a better understanding of genetic regions controlling production of these compounds. The phenotypic data for QTL detection was generated in 2009 from a population of 274 recombinant inbred lines (RILs) separated into three field tests based on maturity (early, mid, and late) and grown in three locations (Knoxville, TN; Harrisburg, IL; and Stuttgart, AR). Genotypic data was obtained using 1,536 single nucleotide polymorphism (SNP) markers, of which 480 were polymorphic. Overall, 21 QTL were detected for soybean isoflavones, including 7 for genistein, 5 for daidzein, 3 for glycitein, and 6 for total isoflavones. Of these 21 QTL, 8 were newly detected, while 13 were validated from previous studies. Marker-assisted selections (MAS) were made using the QTL for genistein, which is typically the most abundant isoflavone, for comparison with phenotypic selections. Challenges exist when considering MAS for quantitative traits such as isoflavones, including concerns with epistatic interactions and genotype × environment interactions. However, isoflavone improvement with MAS would be useful as phenotyping data is costly and time consuming. Comparisons of MAS and phenotypic selection methods were done in 2010 and 2011 in field tests grown in three locations (Knoxville, TN; Springfield, TN; Milan, TN). Results from this study indicate that phenotypic selections outperformed MAS for genistein. However MAS for genistein did show improvements in relation to parental lines, as well as unselected RILs included in field tests for comparison. Additionally, genistein was significantly correlated with other isoflavones, as well as with yield. More research should be done as the costly and time consuming process of collecting phenotypic data for isoflavones provides incentive to pursue MAS as an improvement strategy.

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