Graduate Thesis Or Dissertation


Wheat (Triticum aestivum) Kernel Polymers as Breeding Targets for Improved End-Use Quality Public Deposited

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  • Wheat is a staple food crop with many applications. The composition and quantity of major and minor flour components greatly influence functional dough properties, processing quality, and end-use suitability. Seven to 15% of the weight of wheat flour is protein and the gluten proteins comprise 80-85% of that. The gluten proteins play key roles in bread-making, as they provide the viscoelastic properties needed for dough expansion during fermentation. Gluten mostly consists of two protein types: gliadins and glutenins. High-molecular-weight glutenin subunits (HMW-GS) are a subclass of glutenins. The allelic composition of HMW-GS present in a cultivar strongly influences end-use quality. The overexpression allele Bx7OE at Glu-B1 has been associated with increased dough strength and improved mixing properties. Unlike protein composition, protein quantity is greatly influenced by environmental factors. Wheat grown in the Pacific Northwest (PNW) often produces high grain yield but low grain protein. Thus, the production of hard wheat at the desired percent grain protein is difficult and usually requires high nitrogen (N) input. The goal of the study “The Effects of Field-Applied Nitrogen and High-Molecular-Weight Glutenin Subunit Bx7OE on Baking Quality” was to investigate the potential effect of Bx7OE on bread and bread-making quality. For this purpose, Bx7OE was introgressed from the wheat cultivar ‘Red River 68’ into four different genetic backgrounds from the Oregon State Wheat Breeding Program. Lines with and without the overexpression allele were selected for comparison and analyzed. Field trials were conducted over two years at two locations. Nitrogen was applied at protein-limiting (112 kg ha-1; “low”) and protein non-limiting (336 kg ha-1; “high”) rates to test whether Bx7OE effects dough properties and loaf volumes under sub-optimal grain protein levels. No considerable improvements in mixing properties were observed under the low N treatment. Under the high treatment, Bx7OE significantly (p<0.05) improved dough strength in comparison to no Bx7OE, as measured by midline peak time (MPT), peak force (Rmax), and large unextractable polymeric protein (LUPP). Lines carrying the allelic combination Bx7OE and Dx5+Dy10 produced the strongest doughs. No significant differences in loaf volume between lines with (900.5 ml) and without Bx7OE (866.7 ml) were observed. Bx7OE showed additive effects with alleles at Glu-D1 for most traits. Arabinoxylans (AX) are the major non-starch polysaccharides in wheat. They are minor flour components in terms of quantity, but major components in terms of their impact on wheat flour functionality. They greatly impact dough characteristics due to their water absorption capacity and ability to form gels. They are dietary fiber and hence, are an important component of human diets and have attracted attention for their potential health benefits. In spite of their significance, little is known about their underlying genetic control. The purpose of the study “Genome-Wide Association Studies of Arabinoxylan Content in Wheat Using a Recombinant Inbred Line Population” was to identify phenotypic variation within a recombinant inbred line (RIL) population and to identify single nucleotide polymorphisms (SNPs) associated with arabinoxylan content. The RIL population of 148 individuals was created from a cross between the soft white winter wheat cultivars Xerpha and Bobtail. Plants were grown in two environments. Phenotypic analysis involved the measurement of total arabinoxylans (Total-AX), water-extractable arabinoxylans (WE-AX), and water-unextractable arabinoxylans (WU-AX). A genome-wide association study (GWAS) was performed for SNP identification. Total-AX and WE-AX content ranged from 1.94%-7.46% and from 0.08%-0.82%, respectively. The growing environment had a significant impact on AX content. SNPs associated with Total-AX and WU-AX were found on chromosomes 2B, 3B, and 6A. SNPs associated with WE-AX were found on chromosomes 1D and 7A. Based on our results, we conclude that arabinoxylan content and composition is strongly influenced by the environment and that only little selection gain is to be expected in wheat breeding.
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