INVESTIGATION OF PUTATIVE GENETIC FACTORS ASSOCIATED WITH SOYBEAN [GLYCINE MAX (L.) MERR.] SEED QUALITY TRAITS
Skoneczka, Jeffrey Allen
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Soybeans are an economically important plant, with an annual crop value that consistently exceeds 20 billion dollars in the United States alone. A recent increase in demand for soybeans, stemming from its diverse applications in products such as animal feed, oil, and biofuel, has created an emphasis for soybean breeders in value added cultivars. These cultivars, have improved, or altered, agronomic or seed composition traits, allowing them to be efficiently utilized in a specific niche of the processing industry. Facilitating the development of such cultivars requires a thorough understanding of the genetic factors that affect the manifestation of value added traits. Value added traits investigated in this study include seed sucrose, raffinose, stachyose, and phytate content, seed weight, and maturity. The objective of the first part of this project was to characterize the source of low seed stachyose in soybean line PI200508. Two F2 populations, developed from PI200508 and soybean introductions which exhibited higher seed stachyose content were utilized in a QTL analysis approach that incorporated the use of the Williams82 whole genome shotgun (WGS) sequence (http://www.phytozome.org) in a candidate gene mapping approach. A predicted soybean galactosyltransferase gene was established as a candidate gene due to its observed segregation with the single low stachyose QTL observed on molecular linkage group (MLG) C2 in both populations. Sequencing of this putative gene revealed a unique 3 bp deletion in PI200508. A marker developed to exploit this deletion accounted for 88% and 94% of the phenotypic variance for seed stachyose content in the two experimental populations, highlighting its potential for use in marker assisted selection of the PI200508 source of low raffinose and stachyose. The second part of this project involved QTL analysis of seed sucrose, raffinose, stachyose, and phytate content, as well as seed weight in a linkage map for a F8 RIL population developed from the Glycine max line V71-370 and the Glycine soja introduction PI40712. Analysis across all 20 soybean MLG identified 25 QTL for these traits on MLG A1, A2, C2, D1b, D2, F, G, H, I, L, M, O. Nine of these QTL were supported across multiple environments, indicating that they, and their associated markers, could be useful to breeders working with these traits. The third part of this project used the same F8 RIL linkage map to investigate time to maturity (Reproductive stage R8). V71-370 and PI407162 differ in time to maturity when grown in Virginia, and the RILs developed from this cross displayed a wide range in maturity. Two major QTL were identified on MLG H and L. Examination of the Williams82 WGS sequence in these QTL regions revealed two predicted genes with homology to Arabidopsis thaliana light response and photoperiodism genes which were investigated as candidate soybean maturity genes. Markers developed from these predicted genes showed close association with the observed QTL, and could facilitate the further investigation of this complex trait.
- Doctoral Dissertations