Agronomy and Crop Sciences Commons^™

Deciphering The Genetic Architecture Of Key Female Floral Traits For Hybrid Wheat Seed Production, Juan Jimenez

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

Wheat (Triticum aestivum L.) is a staple cereal that provides 20% of the calories and proteins in human intake (Ray et al., 2013). Global population is projected to increase to 9.7 billion by 2050. Food production must increase by 70% to feed this future population. Wheat production is in crisis due to political and environmental challenges and is projected to decline by 0.8% in 2022 (FAO, 2022). To ensure food security yield genetic gain must increase by around 1.4% annually. Taking advantage of heterosis, hybrid wheat has the potential to boost grain yield. However, hybrid wheat seed production systems …

Nitrification Inhibitor, Nitrogen Source, And Herbicide Effects On Soil Nitrogen Transformations And Corn Yield, William Neels

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

Nitrogen fertilizer management continue to be challenging due to potential nitrogen losses under variable weather conditions. The objective of this was to evaluate the performance of nitrification inhibitors, nitrogen sources and herbicides on in-season nitrogen availability and agronomy indicators. A two site-year field experiment was conducted in silty clay loam soil in corn phase of the corn-soybean rotation at Central Nebraska. The treatments included three herbicide (no pre-emergence, Acuron, Resicore) and five nitrogen treatments: 1) control, 2) anhydrous ammonia, 3) anhydrous ammonia without nitrification inhibitor, 4) urea with nitrification inhibitors, and 5) urea without nitrification inhibitors. Results indicated that nitrogen …

Addressing Challenges Of Dryland Production Of Sunflowers And Corn In The Semi-Arid High Plains Of Nebraska, Zhan Orazov

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

Corn and sunflower are value crops for America. Cultivation of corn and sunflower often vary depending on growing environment. Selecting appropriate planting dates, hybrids and plant density frequently concerns farmers. This concern is understandable because the decision made directly impacts final income. The objectives were to evaluate interaction of corn and sunflower planting dates and hybrid maturity and evaluate interaction of corn flex hybrids and plant density under conditions of western Nebraska. Nine corn hybrids with relative maturity ranging from 86 to 105 days were sown between early May and late June in first and between late April and early …

Mycorrhizae In Maize (Zea Mays L.) Cropping Systems Respond Differently To Nitrogen Fertilization Under Increasing Crop Rotational Diversity, Morgan Mcpherson

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

Arbuscular mycorrhizal fungi (AMF) remain a vital obligate symbiont of nearly all plants. It is well established that the symbiosis between AMF and host plant improves plant nutrient acquisition, alleviates abiotic and biotic environmental stressors, defends against plant pathogens, and contributes to overall plant fitness and productivity through modification of the soil habitat. Modifications include increased soil aggregation and stability, carbon sequestration through provision of fungal wall precursors to soil organic matter (SOM) formation, and enhanced nutrient cycling in the mycorrhizosphere. The goal of this dissertation was to assess how AMF respond to nitrogen (N) fertilization regimes in maize cropping …

Optimization Of Nozzle, Application Height, And Speed For Uass Pesticide Applications, Trenton Houston

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

Unmanned aerial spray systems (UASS) applications have the potential to be efficient pesticide application platforms under conditions that are not accessible or fit for typical pesticide application equipment. Although this type of application is still under development in the U.S., UASS pesticide applications are common in Asia, as they have replaced backpack sprayers. There is limited literature on the optimization of UASS applications and many parameters need to be investigated to identify the best combination of application variables such as flight height, flight speed, and nozzle selection. The objectives were to identify the deposition patterns of a four rotor UASS …

Characterization And Selection Of Hop Cultivars Adapted To Nebraska, Kristina Alas

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

Hop (Humulus lupulus L.) is an ingredient in the beer brewing industry that provides beer its flavor and aroma. High demand from the brewing industry has encouraged production outside of the traditional Pacific Northwest, the primary production region. Producers in the Midwest are attempting to grow cultivars adapted to the Pacific Northwest, but environmental differences have caused low yields and changes in secondary metabolite content. To aid producers, a regional breeding program was initiated to develop cultivars adapted to the Midwest. Success of any breeding program relies on the selection of genetically superior parents to generate progeny with the …

Dicamba Tank Mixtures And Formulations And Their Effects On Sensitive Crops During Cleanout Procedures, Vinicius Velho

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

The introduction of dicamba-tolerant (DT) soybeans (Glycine max L. Merr) and cotton (Gossypium hirsutum L) in 2017 provided an additional tool for herbicide resistant weeds management. In the subsequent years, off-target movement of dicamba allegedly caused damage to sensitive crops and vegetation.

Possible causes of off-target movement include tank contamination, physical drift, and volatility. Additional products, such as herbicides to control grass, are often added to tank with dicamba, which is used to control broadleaf weeds, to increase the spectrum of control and application efficiency. Dicamba products registered for DT crops require the use of drift reducing …

Recombination Hotspots In Soybean [Glycine Max (L.) Merr.], Samantha J. Mcconaughy

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

Recombination allows for the exchange of genetic material between two parents which plant breeders exploit to make new and improved varieties. This recombination is not distributed evenly across the chromosome. In crops, it mostly occurs in the euchromatic regions of the genome and even then, recombination is focused into recombination hotspots flanked by recombination cold spots. Understanding the distribution of these hotspots along with the sequence motifs associated with them may lead to methods that enable breeders to better exploit recombination in breeding.

In chapter 1 background information on recombination, recombination hotspots detection methods, landscape of recombination (describe recombination patterns …

Water Quality, Carrier Volume And Droplet Size Effects On Herbicide Efficacy And Drift Potential, Barbara Houston

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

Herbicide performance is directly related to the amount of active ingredient that has been deposited on the plant. Hence, spray solution characteristics and application parameters are crucial in determining the efficacy of an herbicide application. To maximize the effectiveness of chemical control, methods to deliver full chemical dose must be utilized: allowing the active ingredient to be readily absorbed once added to the carrier and mitigating off-target movement and low herbicide doses. Water is the most frequently used carrier in herbicide applications. Chemical parameters, such as water hardness and pH, can have a critical role in herbicide performance. It is …

Regional Plant Community Differences In The Nebraska Sandhills, Travis Millikan

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

The Nebraska Sandhills is very valuable to the state of Nebraska, representing one of the most in-tact and largest grassland ecosystems in temperate regions in the world. Rangeland managers must understand plant community dynamics across the Sandhills to better inform management decisions. The first objective of this study was to evaluate plant community variability on upland Sands ecological sites across different precipitation zones in the Nebraska Sandhills. The second objective of our study was to utilize the Rangeland Analysis Platform (RAP) to examine spatial and temporal variability in biomass production and cover on pastures of ranches analyzed in the first …

Exploration Of Genes Controlling Grain Yield Heterosis In Hybrid Wheat (Triticum Aestivum L.) Utilizing 3ʹ Rna Sequencing, Nichole Miller

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

The implementation and future success of hybrid wheat (Triticum aestivum L.) is impacted by breeders’ inability to create consistent high yielding, high heterosis hybrids. This research addresses this problem by conducting an exploration of transcriptomes from hybrids and parent lines to determine what genes are active in heterotic or non-heterotic hybrids and how their level of expression can explain the phenotype of grain yield heterosis. Using hybrids that showed positive mid-parent heterosis (MPH), classified as heterotic in our study, and negative or no difference MPH hybrids, classified as non-heterotic, differentially expressed genes (DEGs) potentially related to heterosis and hybrid …

Evaluating Traits Influencing Hybrid Wheat Seed Production Using A Double Haploid Population Derived From Freeman X Camelot, Emre Karahan

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

Hybrid wheat (Triticum aestivum L.) cultivars are preferred for their advanced agronomic traits such as a yield improvement increase up to 20%. However, hybrid cultivars remain difficult to produce on a commercial scale due to inadequate pollen dispersal, the closed nature of the wheat floret and the high cost of inducing sterility or restoring fertility in cleistogamous wheat. Redesigning parent-specific traits and understanding their potential interactions with related agronomic traits are needed to breed improved male lines in hybrid seed production fields. To better understand the genetic control of anther extrusion (AE), 174 double haploid lines derived from Freeman …

Winter Cover Crop Impacts On Weed Dynamics In Eastern And Central Nebraska, Elizabeth Ann Oys

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

Reducing tillage in cropping systems causes weed management to be dependent on chemical and cultural methods for weed control. Over time, herbicide-resistant weeds have developed due to the continuous selection pressures from herbicides, particularly in the Midwest Corn Belt. Integrated weed management strategies, such as cover crops, can be used to mitigate some of these issues. Cover crops are primarily known for their soil health benefits, but there is evidence that cover crops can suppress weeds. However, less research has been done at the field-scale level to address cover crop impacts on the weed seedbank and aboveground weeds during the …

Cattle Diet Selection During The Growing Season On Upland Sandhills Rangelands, Alejandro Orozco-Lopez

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

The Sandhills is a diverse and complex ecosystem comprised of different topographic positions (i.e. slopes and interdunes) that influence grazing distribution, plant species composition, and cattle diet selection. The first objective of this study was to evaluate how grazing intensity influences species composition on slopes and interdunes on native rangeland within the Hillside pasture (160 ha) at the UNL Gudmundsen Sandhill’s Laboratory (GSL). The second objective of this study was to evaluate forage quality of individual species from three plant functional groups (i.e. warm-season grasses, cool-season grasses, and forbs/shrubs) on native rangeland within the Hillside pasture (160 ha) at GSL. …

Characterization Of Salt And Drought Tolerance In Sunflower (Helianthus Annuus L.), Sevgi Saylak

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

Consequent to the increasing world population, food sources are needed to be increased to meet the nutritional needs. However, due to natural processes and agricultural activities, the most destructive environmental factors that limit crop production, soil salinity, and drought-exposed areas are growing. As one of the major oilseed crops, sunflower (Helianthus annuus L.), is considered to be moderately tolerant to salt and drought. Although it can grow in arid to semi-arid regions, increasing salinity and drought might adversely affect sunflower production. This study aimed to investigate several sunflower germplasms' morphological responses to salt and drought stresses. For this purpose, …