Management Zone Delineation Techniques On Irrigated Corn In Nebraska, Aaron M. Bereuter

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Increased interest in site-specific management of irrigated corn in Nebraska has identified the need for a decision-making framework for zone delineation. Zones based on static soil and landscape properties provide a valuable foundation for variable rate management strategies. The purpose of this project was to identify the optimal soil and landscape attributes for generating management zones (MZ) of relative productivity potential. Three producer-managed cornfields across Nebraska with varying soil types, topographic characteristics, and climate regimes were identified as research sites during the 2010 growing season. Nine soil and landscape attributes were identified as potential properties for estimation of productivity potential. …

Identification Of Soybean Seed Oil Qtls With Little Or No Impact On Seed Protein, Yu-Kai Sun

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

A QTL (Quantitative Trait Locus) is chromosomal location of a gene controlling a specific phenotypic characteristic (trait). This trait might be governed by two or more genes and may be affected by environmental interaction. The USA soybean seed composition, when averaged over years and states, is 18.7% oil and 35.3% protein. Soybean seed provides cooking oil for humans and protein for livestock. Concurrent genetic improvement of seed protein (pro) and oil content has been difficult to achieve due to the negative genetic correlation of the two traits. This negative correlation could be due to a pair of tightly linked protein …

Impact Of Crop And Residue Management On The Physical And Chemical Stabilization Of Soil Organic Matter At Farm Level, Ana B. Wingeyer

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

This dissertation explores changes over time in soil organic matter (SOM) stabilization of two irrigated production fields: a continuous maize sequence that was converted from no-till to conservation deep tillage (Site 1), and a no-till maize-soybean rotation (Site 2). An integrated approach using humic acid extractions and density-based physical fractionation of SOM within aggregate size classes was developed to evaluate the changes in SOM stabilization (physical protection, organo-mineral associations and humification). At Site 1, loss of SOM in the surface layer was compensated for by increased SOM in deeper soil layers with no net change in C stocks. Whole field …

Integration Of Plant-Based Canopy Sensors For Site-Specific Nitrogen Management, Luciano S. Shiratsuchi

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

The soil’s nitrogen (N) supply can vary drastically in the field, spatially as well as temporally making any soil prediction difficult even with very detailed mapping. Consequently, a plant-based approach wherein the measured canopy can indicate the N needs in a reactive and spatially-variable way can be a better approach than mapping, because integrate the soil N supply and translate the crop need on-the-go. The first experiment evaluated the performance of various spectral indices for sensing N status of corn, where spectral variability might be confounded by water-induced variations in crop reflectance. We found that water and previous crops effects …

Genetics Of Polyphenol Oxidase (Ppo) Activity In Wheat (Triticum Aestivum L.), Somrudee Onto

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

The enzyme activity of polyphenol oxidase (PPO) in grain is regarded as a major factor in time-dependent darkening and discoloration of wheat food products during processing or storage. The darkening phenomena of products reduce the quality of products and affect consumer acceptance. Breeding wheat cultivars with low PPO activity is the best way to reduce the undesirable darkening. The low PPO line PI 117635 was crossed to two low PPO wheats from Idaho, IDO580 and IDO377s to determine whether matings between wheats with low levels of grain PPO would result in complementation, and lines with lower or nil PPO would …

The Rate Of Shattercane X Sorghum Hybridization In Situ, Jared J. Schmidt

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Cultivated sorghum (Sorghum bicolor subsp. bicolor) can interbreed with its close weedy relative shattercane (S. bicolor subsp. drummondii). The introduction of traits from cultivated sorghum into a shattercane population could contribute to the invasiveness of the wild shattercane population. An in situ experiment was conducted across two years to determine the potential for pollen-mediated gene flow from grain sorghum to shattercane. Shattercane with juicy midrib (dd) was planted in a soybean field in concentric arcs at varying distances from a sorghum pollen source with dry midrib (DD). The arcs were placed so …

Disease And Insect Resistance And Quality Characterization Of Six Cimmyt Synthetic Hexaploid Wheats, Kayse Onweller

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

The germplasm sources of common wheat (Triticum aestivum L.) are eroded by selection pressures applied by plant breeders and the disappearance of landraces. The erosion causes a loss of potentially useful resistance genes, among other agronomic and quality genes. Continuously changing pathogen races and insect biotypes affecting the Great Plains requires identification of new sources of resistance. Synthetic hexaploid wheats (SHWs), T. turgidum (BBAA) x T. tauschii (DD) hybridizations, offer ways to utilize resistances trapped in the diploid and tetraploid ancestors of common wheat. Six SHWs were assayed for resistance to a variety of fungal diseases, viruses, and aphids …

Hydrologic Effectiveness And Plant Survivability In The Holmes Lake Rain Garden Pilot Program: Year Three, Marilyn K. Liebsch

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Rain gardens are increasingly being used as small scale stormwater best management practices (BMPs) to reduce stormwater runoff through infiltration and to remove pollutants through filtration. In 2007, as part of a comprehensive water quality restoration process of Holmes Lake in Lincoln, Nebraska, 20 pilot rain gardens were installed in residential and school properties in the watershed. Currently, assessment and monitoring has been limited to participant surveys and cannot be used to determine if hydraulic or vegetative problems exist within the garden area. In this study, visual inspections were conducted to establish a database standard for successful rain gardens, hydraulic …

Gata-Family Transcription Factors In Magnaporthe Oryzae, Cristian F. Quispe

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

The filamentous fungus, Magnaporthe oryzae, responsible for blast rice disease, destroys around 10-30% of the rice crop annually. Infection begins when the specialized infection structure, the appressorium, generates enormous internal turgor pressure through the accumulation of glycerol. This turgor acts on a penetration peg emerging at the base of the cell, causing it to breach the leaf surface allowing its infection.

The enzyme trehalose-6- phosphate synthase (Tps1) is a central regulator of the transition from appressorium development to infectious hyphal growth. In the first chapter we show that initiation of rice blast disease requires a regulatory mechanism involving an …

Evaluation Of Algorithm Thresholds For Crop Canopy Sensor-Based In-Season Nitrogen Application In Corn, Brian T. Krienke

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Nitrogen fertilizer is frequently the most limiting nutrient in corn production. Typically most nitrogen is applied before planting. Since nitrogen can leave the soil system fairly easily, the result can be an inefficient use of nitrogen fertilizer. Previous research has shown increased efficiency with no reduction in yield by applying nitrogen later in the season when the crop is actively growing, with rates regulated spatially through the use of active crop canopy sensors. This study evaluated the potential for N cutoff thresholds using a sufficiency index as the threshold value for areas with poor stand or an unrecoverable N deficiency. …

Transpiration-Use Efficiency Coefficient Of Seven Weed Species As Affected By Fraction Of Transpirable Soil Water And Growth Stage, Venkatarao Mannam

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Transpiration-use efficiency coefficient (Kc) describes the amount of biomass produced per unit transpiration at a given vapor pressure deficit. A series of greenhouse experiments were conducted to determine the K_c values of seven weed species and to measure how K_c values were affected by fraction of transpirable soil water (FTSW) level and plant growth stage. Experiments were conducted using a factorial design with 4 levels of water stress (0.3, 0.4, 0.7, and 1.0 FTSW) and two harvest times (first bloom and seed maturity). After plants attained a predetermined size, each plant was sealed at the base using a …

Remarkable Features Of The Hotdog-Fold Thioesterases Involved In Phylloquinone (Vitamin K1) Biosynthesis, Joshua R. Widhalm

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Phylloquinone (vitamin K₁) is a bipartite molecule, consisting of a naphthoquinone ring attached to a phytyl side chain, that is synthesized by plants and certain cyanobacteria to serve as an electron carrier in photosystem I. The coupling of the ring and isoprenyl moieties relies on the cleavage of the CoA-thioester linkage with 1,4-dihydroxy-2- naphthoate (DHNA). It has long been a mystery if this hydrolysis is an enzymatic or chemical process. Using comparative genomics, protein biochemistry, genetics and metabolic profiling, we identified a cyanobacterial thioesterase responsible for the in vivo hydrolysis of DHNA-CoA. This enzyme bears a signature domain …

Herbicide-Resistant Risk Assessment: Response Of Common Nebraska Weeds To Dicamba Dose, Roberto J. Crespo

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Dicamba-resistant soybeans are being developed to provide an additional herbicide mechanism of action that can be used in soybean, and to provide a tool to help manage or mitigate the evolution of other herbicide-resistant weed populations. The objectives of this thesis were to assess the risk of common Nebraska weeds developing resistance to dicamba, quantify baseline dose-response to dicamba of high-risk weed species, and survey the variability in dicamba dose-response among populations of those species. Twenty-five weed scientists were asked to estimate the risk likelihood of ten weed species evolving resistance to dicamba following the commercialization of dicamba-resistant soybean. Palmer …

Biology, Systematics, Phylogenetic Analysis And Dna Character-Based Species Diagnosis Of The False Root-Knot Nematode Nacobbus Aberrans (Thorne, 1935) Thorne & Allen 1944 (Nemata:Pratylenchidae), Angel Ramirez-Suarez

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

The False Root-Knot nematode Nacobbus aberrans is a plant parasitic nematode that causes yield losses in several crops and plant protection agencies have established regulations to prevent infestations from spreading to new agricultural areas. The taxonomic status of the nematode has been the subject of controversy due to wide degree of variation exhibited by the species. This variability has led to the suggestion that N. aberrans is actually a species complex rather than a single species. In order to test this hypothesis, we compared twelve N. aberrans populations, which include isolates from western Nebraska, two distinct regions of Mexico and …

Evaluating Commercially Available Diagnostic Tests For The Detection Of Clavibacter Michiganensis Subsp. Nebraskensis, Cause Of Goss's Bacterial Wilt And Leaf Blight In Corn, Kevin A. Korus

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Goss’s wilt and blight of corn, caused by the bacterium Clavibacter michiganensis (Cm) subsp. nebraskensis (Cmn), is currently diagnosed by symptom identification and successful isolation onto CNS selective medium. An ELISA test kit and ImmunoStrips (Agdia^®) specific to Cm michiganensis (Cmm) reportedly give a cross-reaction with Cm subspecies. Also, the GEN III OmniLog Identification system (Biolog Inc., Hayward, CA) is said to provide accurate identification of Cm subspecies. These tests would provide a quick and inexpensive method for diagnosis of Cmn but have not been previously validated. ELISA test kits were provided by Agdia for the detection of …

Impact Of Student Motivation In Online Learning Activities, Amy Lathrop

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

With the prevalence of online learning in education for both distance and campus-based students, it is critical to determine how to design electronic learning materials that tailor to student motivation and facilitate learning. Students were asked to complete an online plant breeding activity, motivation survey and an online learning quiz related to the activity. The control group of students was those who elected not to complete the activity, while the experimental group of students chose to complete the activity. Motivation scores were compared between control and experiment groups, courses, and gender using independent sample t-tests. Pearson correlations were also used …

Characterizing The Chemoprevention Potential Of Amenity Grass Phenolic Extracts In Vitro And The Corresponding Nutraceutical Targets Within Hepg2 Carcinoma Cells, Casey J. Wegner

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

This research has revealed significant chemopreventive potential belonging to the planet’s most renewable and abundant plant source: amenity grasses. The characterization results from Chapter 1 demonstrated the potential chemoprevention attributes of supina bluegrass and bermudagrass crude extracts linked to the extensive phenolic acid profiles of these amenity grasses. In contrast to cereals, amenity grass phenolic extracts (AGPE) offer appreciable amounts of unbound/free ferulic acid that would be available for rapid in vivo absorption. The literature has shown ferulic acid to be a highly available and health benefitting phenolic compound. Chapter 1 in vitro studies demonstrated AGPE-induced antiproliferation and apoptotic induction …

Twin-Row Production And Optimal Plant Population For Modern Maize Hybrids, Mitchell J. Novacek

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Maize (Zea mays L.) is widely grown for food, feed, and fuel, and optimal yield will be required to meet increasing demand due to world population growth and increased biofuel usage. This requires matching of the best maize hybrids with optimal plant population and spacing. Modern maize hybrids have increased “crowding stress” tolerance, and Bt (Bacillus thuringiensis) hybrids now resist European corn borer and corn rootworm which has created interest in altering row configuration and increasing plant population.

Three Bt hybrids were evaluated from 2009 to 2010 near Mead, NE at target populations from 69136 to 106173 …