Date of Graduation

8-2014

Document Type

Dissertation

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Chen, Pengyin

Committee Member

Clark, John R.

Second Committee Member

Sharpley, Andrew N.

Third Committee Member

Mauromoustakos, Andronikos T.

Fourth Committee Member

Wang, Ya-Jane

Keywords

QTL; Soybean; Stachyose; Sucrose

Abstract

Seed carbohydrate content is an important aspect in breeding for food-grade soybeans commercialized in the soyfood market. Sucrose and stachyose are the primary carbohydrates in soybean seed. Sucrose affects the quality and taste of various soyfoods such as tofu, soymilk, and natto; however, consumption of soy-based products with high stachyose concentrations can cause diarrhea and flatulence. A mutant line (V99-5089) with high-sucrose and low-stachyose has been identified. The objectives of this research were: 1) to identify sucrose QTLs in a F2-derived mapping population; 2) to investigate the genetic relationship between two low-stachyose sources, V99-5089 and the germplasm line PI200508; and 3) to identify stachyose QTLs in a F2-derived mapping population. An allelism test for low stachyose was performed by using 121 F2-derived lines from the cross PI200508 x V99-5089 grown in three different environments. Carbohydrate content was determined by a high performance liquid chromatogram system, and lines were classified as high- or low- stachyose. Chi-square analysis was performed to test for goodness-of-fit of observed segregation to the expected genetic ratio. Results showed a 9 high-stachyose : 7 low-stachyose ratio, indicating that two independent recessive genes conferred the low-stachyose trait in the two mutant lines. Additionally, gene dosage effect was observed; however, further study is required in order to confirm its presence. The sucrose and stachyose QTL studies were carried out in 92 F2:7 lines derived from the cross V97-3000 x V99-5089. Leaf samples were collected at F2:6 for DNA extraction and subsequent molecular analysis using single nucleotide polymorphism (SNP) markers. Seed from F2:7 lines grown in two locations, each one with two replications, were analyzed for sugar content. Results showed two sucrose QTLs located on chromosomes 6 and 10, accounting for 17 and 11% of the phenotypic variation, respectively. Additionally, two stachyose QTLs were found on chromosome 10 and 11, explaining 11 and 46% of the stachyose variation. Results from this research indicate that the two low-stachyose sources may serve as valuable parents in breeding for low-stachyose soybeans. Additionally, V99-5089 may also provide favorable alleles for breeding high-sucrose varieties. The sucrose and stachyose QTLs identified in these studies are stable across environments and will facilitate the marker-assisted selection for both traits.

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