UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item POSITIONAL CLONING OF BROAD-SPECTRUM LEAF RUST RESISTANCE GENE, LR57, FROM AEGILOPS GENICULATA, A TERTIARY GENE POOL MEMBER OF WHEAT(2023) Schulden, Taylor Francis; Rawat, Nidhi; Erwin, John; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The tertiary gene pool of wheat includes wild relatives like Aegilops geniculata (UUMM, 2n=4x=28) that are valuable genetic reservoirs for novel abiotic and biotic resistance genes. However, modern wheat varieties share limited genomic commonality with these gene pool members presenting barriers to recombination and genetic mapping of desirable genes. We mapped a broad-spectrum leaf rust resistance gene Lr57 located on chromosome 5Mg of Ae. geniculata using a simple but powerful methodology for high-resolution genetic mapping in tertiary gene pool members of wheat. Five gene candidates were revealed all with possible defense related functions. Strategic application of differential expression analysis, Virus-Induced Gene Silencing, and mutagenesis analysis reduced the candidate gene of interest to a singular and novel ID-NLR resistance gene containg a protein kinase, NB-Arc, and LRR domain. Using multiple strategies, validation of Lr57 candidate was completed. Gene complementation by transformation of Lr57 candidate is currently being conducted.Item A NEW APPROACH FOR FINE MAPPING AND CLONING GENES FROM THE TERTIARY GENE POOL MEMBERS OF WHEAT: EXAMPLE OF LR57 FROM AEGILOPS GENICULATA(2020) Steadham, James; Rawat, Nidhi; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wheat is a staple food for 35% of the world’s population, providing more calories and protein to the world’s diet than any other crop. Wheat rust diseases cause yield losses worth billions of dollars annually. Two rust resistance genes, Lr57 and Yr40, conferring leaf rust and stripe rust resistance, respectively, were previously identified in a wild wheat relative, Aegilops geniculata. Mapping these genes within a wheat background is typically impossible, due to the absence of genetic recombination between wheat and wild species chromatin. We devised a novel technique to overcome this barrier, developing a mapping population from a cross between a resistant Ae. geniculata-wheat introgression line and a susceptible Ae. geniculata disomic addition line. Genotyping and phenotyping 162 individuals from this population, we found 11 recombinants within a 6 Mb interval and fine mapped Lr57, demonstrating the high-resolution power of this strategy for mapping genes from wild relatives of wheat.Item Genetic Control of Flowering Time in a Soft Red Winter Wheat Doubled Haploid Population(2015) Miller, Daniela Michelle; Costa, Jose M; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Flowering time in wheat is regulated mainly by response to seasonal environmental cues and controlled by the photoperiod and vernalization pathways. Allelic diversity in genes controlling these pathways is used by breeders to adapt wheat for optimal yield in a broad range of environments. This study characterized genetic loci influencing heading date in a soft red winter wheat doubled haploid population. Two photoperiod insensitivity alleles, Ppd-A1a and Ppd-D1a, were found to have major effects in eight field locations. The Ppd-A1 locus explained up to 16.8% of variation in heading date, whereas the Ppd-D1 locus explained up to 39.7%. In reduced vernalization greenhouse experiments, a QTL in the same region as the VRN-A1 gene explained up to 42.4% of variation in heading date, suggesting that the population differed in this region. Assays for previously-described allelic diversity in the VRN-A1 gene, however, did not detect any polymorphism between parents of the population.Item A GENERALIZED APPROACH TO WHEAT YIELD FORECASTING USING EARTH OBSERVATIONS: DATA CONSIDERATIONS, APPLICATION, AND RELEVANCE.(2012) Becker-Reshef, Inbal; Justice, Christopher C; Vermote, Eric; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In recent years there has been a dramatic increase in the demand for timely, comprehensive global agricultural intelligence. The issue of food security has rapidly risen to the top of government agendas around the world as the recent lack of food access led to unprecedented food prices, hunger, poverty, and civil conflict. Timely information on global crop production is indispensable for combating the growing stress on the world's crop production, for stabilizing food prices, developing effective agricultural policies, and for coordinating responses to regional food shortages. Earth Observations (EO) data offer a practical means for generating such information as they provide global, timely, cost-effective, and synoptic information on crop condition and distribution. Their utility for crop production forecasting has long been recognized and demonstrated across a wide range of scales and geographic regions. Nevertheless it is widely acknowledged that EO data could be better utilized within the operational monitoring systems and thus there is a critical need for research focused on developing practical robust methods for agricultural monitoring. Within this context this dissertation focused on advancing EO-based methods for crop yield forecasting and on demonstrating the potential relevance for adopting EO-based crop forecasts for providing timely reliable agricultural intelligence. This thesis made contributions to this field by developing and testing a robust EO-based method for wheat production forecasting at state to national scales using available and easily accessible data. The model was developed in Kansas (KS) using coarse resolution normalized difference vegetation index (NDVI) time series data in conjunction with out-of-season wheat masks and was directly applied in Ukraine to assess its transferability. The model estimated yields within 7% in KS and 10% in Ukraine of final estimates 6 weeks prior to harvest. The relevance of adopting such methods to provide timely reliable information to crop commodity markets is demonstrated through a 2010 case study.Item Scab Resistance QTLs are Associated with Quality and Agronomic Traits of Soft Red Winter Wheat(2011) Cardwell, Lydia Ann; Costa, Jose; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fusarium head blight (FHB) is a devastating fungal disease affecting Triticum aestivum crops worldwide. While many quantitative trait loci (QTL) responsible for FHB resistance have been reported, some widely used sources are from exotic cultivars that may carry undesirable alleles linked with resistance. Ning_7840, a Chinese hard red spring wheat, contains a major FHB QTL on the 3BS chromosome, along with two minor QTL on the 5A and 2DL chromosomes. Ning_7840 was crossed with Pioneer_2643, a soft red winter wheat, to create 86 recombinant inbred lines. The effect of the Ning_7840 alleles on agronomic traits and milling and baking quality traits was examined over three growing seasons in Maryland. While the 3BS QTL was not associated negatively with other traits, the 2DL and 5A QTL were. This suggests the introduction of FHB resistance QTL on 5A and 2DL into soft red winter wheat may negatively affect agronomic and quality traits.Item Promoting the production and consumption of wheat-based functional foods rich in antioxidants.(2008-11-20) Luther, Marla West; Yu, Liangli; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The present study evaluated the effects of solid state yeast treatment and thermal processing on the extractability and in-vitro bioavailability of antioxidants from wheat bran and whole-wheat pizza crusts, and developed sample outreach materials for promoting the consumption of whole-wheat functional foods. The first section analyzed the effect of solid-state yeast treatment on the extractable antioxidant properties of wheat bran. Wheat bran was treated with ten commercially available food grade yeasts under solid state conditions. Antioxidant properties were evaluated by measuring total phenolic content, and radical scavenging capacities against the cation ABTS, peroxyl (ORAC), DPPH (RDCS), and hydroxyl (HOSC) radicals. Results showed that under the selected conditions, yeast strain LBE.11 was able to increase ORAC and HOSC radical scavenging by 50% and 67%, respectively. The second part of this study evaluated the impact of bran particle size, fermentation time, and baking time and temperature on the 100% ethanol extractable antioxidant capacities of whole wheat pizza crust. Results showed that pizza crusts produced with reduced bran particle size maintained antioxidant capacity throughout thermal processing. At 18 hrs of fermentation RDSC and TPC values of the pizza crusts were increased by 17% and 23%, respectively. Increasing baking temperature increased RDSC values by 14 and 17% for pizza crusts prepared with Lakin and Trego variety wheat, respectively. The third part of this study analyzed the in-vitro bioavailability of wheat antioxidants in baked pizza crusts. Antioxidant properties were evaluated by measuring total phenolic content, and radical scavenging capacities against the cation ABTS, peroxyl (ORAC), DPPH (RDCS), and hydroxyl (HOSC) radicals. Pizza crusts with higher available antioxidants may have a greater level of bio-available antioxidants. The final segment of this research was to develop a tri-fold for promoting the consumption of whole wheat foods. The tri-fold was designed to include food-specific knowledge, consumption consequences knowledge in addition to recipes and directions, and nutritional facts. Integrating research findings into outreach materials may be an effective way to increase functional food consumption. Results from these studies indicate that there are numerous ways to increase antioxidant levels in the diet.Item Enhancing the availability of natural antioxidants in wheat-based food ingredients and food products through improved post-harvest treatments and processing conditions(2007-04-20) Moore, Jeffrey Calvin; Yu, Liangli; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wheat grain has significant antioxidant contents concentrated in the bran fraction, most of which may not be bioavailable in humans because they are not released from matrix materials during digestion. The present study developed solid-state enzymatic and yeast post-harvest treatments, and investigated the effects of these treatments and food processing on the extractable antioxidant properties of whole-wheat based food ingredients and food products. Antioxidant properties investigated in this study included scavenging capacities against cation ABTS radicals, peroxyl radicals (ORAC), hydroxyl radicals, and DPPH radicals, and total phenolic contents and phenolic acid compositions. The first part of this research developed and validated a high-throughput fluorometric hydroxyl radical scavenging capacity (HOSC) assay. The HOSC assay utilized a Fe(III)/H2O2 Fenton-like reaction to generate hydroxyl radicals, fluorescein as detector probe, trolox as an antioxidant standard, and area under the curve measurements to quantify scavenging capacity. The hydroxyl radical purity and potential solvent interference in the assay system were evaluated using electron spin resonance. The HOSC assay was found to have acceptable performance characteristics including linear range, accuracy, and reproducibility. The second part of this study investigated the potential of solid-state enzyme and yeast treatments to improve wheat bran antioxidant properties. Both enzyme and yeast treatments were capable of increasing available wheat bran antioxidant properties. Reaction parameters found to influence the effectiveness of these treatments to enhance wheat bran antioxidant properties included enzyme preparation and reaction moisture content for enzyme treatments, and yeast preparation along with dose and treatment time for yeast treatments. The final part of this research evaluated the effects of processing conditions including bran particle size, fermentation time, and baking conditions on the antioxidant properties of a whole-wheat pizza crust. Baking increased extractable antioxidant properties up to 82%. Fermentation time caused some significant increases, while bran particle size had no influence on extractable whole-wheat pizza crust antioxidant properties. This study suggests that post-harvest treatment of wheat bran and optimized processing conditions for whole-wheat food products are potential approaches for increasing their extractable antioxidant properties.Item PHYTOCHEMICAL PROFILES AND ANTIOXIDANT PROPERTIES OF WHEAT(2005-07-28) Zhou, Kequan; Yu, Liangli; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The present study examined and compared wheat grain, bran, aleurone, and micronized aleurone for their antioxidant properties and phytochemical profiles. The results showed that wheat antioxidants were concentrated in bran fraction, particularly in the aleurone layer of wheat bran. Micronized aleurone demonstrated the highest antioxidant activities (scavenging activities against ABTS+, DPPH, ORAC, and chelating activity), and the highest total phenolics and phenolic acids concentration, suggesting that post-harvest treatment may affect the availability of wheat antioxidants. The present +study also investigated bran samples of seven wheat varieties from four different countries for their antioxidant properties and phytochemical profiles. The bran samples exerted enormous differences in concentrations among their phenolic acids, tocopherols and carotenoids. Their antioxidant activities were also notably different from 13% (scavenging capacity against O2-) to 99% (ORAC). These data suggest that wheat varieties and growing conditions might alter wheat antioxidant properties and phytochemical compositions. In addition, eight selected Maryland grown soft wheat varieties or experimental lines were examined for potential beneficial components and antioxidant properties. These soft wheat varieties significantly differed in their ABTS+ scavenging activity and chelating activity. Significant amount of phenolic acids have been demonstrated in all soft wheat grain. But their phenolic acid content markedly differed among different varieties which mainly (89% - 94%) existed as the insoluble bound form with ferulic acid as the predominant phenolic acid. These data suggest the possibility to produce soft wheat varieties rich in selected health beneficial factors for optimum human nutrition through breeding programs. Finally, five phenolic acids commonly present in wheat grain and fractions were examined and compared for their radical scavenging properties and chelating capacities using spectrophotometric and electron spin resonance measurements. These phenolic acids differed in their properties to react with and quench HO, O2-, ABTS+, and DPPH, as well as their capacities to form chelating complexes with transition metals. Strong structure-activity relationships were observed in the present study. Both substitutes on the phenyl ring and the conjugated carbon skeleton may influence the antioxidant properties of these phenolic acids.