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Cover Crop Effects On Maize Productivity: Insights From Statistical And Process-Based Models, Guillermo Marcillo Jan 2018

Cover Crop Effects On Maize Productivity: Insights From Statistical And Process-Based Models, Guillermo Marcillo

Graduate Theses and Dissertations

Winter cover crops can be an effective strategy to buffer soil and water impairing effects from intensively managed agriculture. While cover crops have shown potential to sequester off-season nitrate, control weeds, or promote nutrient cycling, knowledge gaps persist in regard to maize impacts driven by cover crop decision making. In this context, statistical and process-based models can be valuable tools for predicting changes in maize systems that include a winter cover crop. In a meta-analysis combining peer-reviewed research from several regions in the US, grain yields were found to change between 0 and 21% when maize (Zea mays L.) followed ...


Environments-By-Design: Developing New Tools To Bring “Field Conditions” To The Laboratory, Kara Lind Jan 2018

Environments-By-Design: Developing New Tools To Bring “Field Conditions” To The Laboratory, Kara Lind

Graduate Theses and Dissertations

Maximizing agricultural yields is an urgent priority for our society as the world population will increase to 9 billion by 2050. Additionally, climate change could have detrimental effects on food supply and biomass production. Addressing these problems means considering the relationship the environment has on a plant’s development. The reality is though that there are few tools to plant scientists that can properly control and monitor the growing environment for plant. We believe that as engineers we can provide plant scientists with new tools which we call “environments by design”. These tools can control the environmental stimuli either abiotic ...


Phenotypic And Genomic Selection For Multi-Trait Improvement In Soybean Line And Variety Development, Andreomar Kurek Jan 2018

Phenotypic And Genomic Selection For Multi-Trait Improvement In Soybean Line And Variety Development, Andreomar Kurek

Graduate Theses and Dissertations

Marker technologies have allowed soybean breeding to exploit genotypic information for traits of various genetic architectures. However, the incorporation of technologies have had qualitative impacts on resources used in variety development projects. The objective of this study was to investigate the impact of integrating Marker Assisted Selection (MAS) for single gene and oligo-genic traits and Genomic Selection (GS) for yield in soybean variety development projects through use of simulations, decision classifier metrics, and cost analysis. The breeding goals of the project are to maximize yield of soybean varieties adapted to maturity zones (MZs) II, III and IV, while assuring that ...


Winter Cereal Rye And Selected Brassica Cover Crops For Forage Prior To Soybeans, Timothy James Sklenar Jan 2018

Winter Cereal Rye And Selected Brassica Cover Crops For Forage Prior To Soybeans, Timothy James Sklenar

Graduate Theses and Dissertations

Despite myriad benefits to incorporating winter cover crops into conventionally managed row crop systems farmer adoption remains low in Iowa. Commonly cited apprehensions include the costs associated with managing cover crops without any short term economic benefits and the complexities associated with management of cover crops. The management of cover crops as a forage could potentially help address both of these issues while at the same time enhancing the environmental sustainability of conventionally managed systems. The work provided in this thesis is an attempt to evaluate the potential for four selected species to be managed as dual-purpose winter cover crops ...


Genetic Dissection Of Photosynthetic Traits In Sorghum Under Cold And Drought Stress, Diego Ortiz Jan 2018

Genetic Dissection Of Photosynthetic Traits In Sorghum Under Cold And Drought Stress, Diego Ortiz

Graduate Theses and Dissertations

Sorghum (Sorghum bicolor L. Moench) is one of the most important cereal crops cultivated in arid and semiarid regions for food, feed and biofuel production. Cold and drought stresses reduce photosynthesis in sorghum, limiting biomass production and yield. It is necessary to understand the genetic mechanisms controlling stress response to develop cultivars with increased cold and drought tolerance. We performed genome wide association studies (GWAS) for gas exchange and chlorophyll fluorescence traits in sorghum. The main objective was to discover genes/genomic regions that control the photosynthetic capacity under optimal, low temperature and drought stress conditions. Two experiments were conducted ...


Biological Roles Of Small Rnas Expressed During Infection Of Barley By The Obligate Fungal Biotroph, Blumeria Graminis F. Sp. Hordei, Matthew Robert Hunt Jan 2018

Biological Roles Of Small Rnas Expressed During Infection Of Barley By The Obligate Fungal Biotroph, Blumeria Graminis F. Sp. Hordei, Matthew Robert Hunt

Graduate Theses and Dissertations

Plants and their pathogens have constantly co-evolving mechanisms that determine infection success. Small RNAs (sRNAs) of 18-30 nucleotides can have a large effect regulating plant defense responses as well as fungal virulence factors. The goal of this project was to understand how sRNAs regulate gene expression both for species of origin, as well as trans-kingdom sRNA communication between barley and Blumeria graminis f. sp. hordei (Bgh), the causal agent of barley powdery mildew. To accomplish this goal we examined Bgh sRNA expression over a time course representing the key stages of Bgh infection of barley (appressorium formation, penetration of epidermal ...


Effects Of Overstory Tree Species And Seed Trap Design On Seed Rain In A Tropical Rainforest, Bridgette Kirk Jan 2018

Effects Of Overstory Tree Species And Seed Trap Design On Seed Rain In A Tropical Rainforest, Bridgette Kirk

Graduate Theses and Dissertations

Tropical rainforests maintain a high diversity of plant species, but the community assembly mechanisms by which this occurs are unclear. We hypothesized that individual overstory tree species could filter seed rain differentially, owing to differences in species-specific traits that affect forest physiognomy and resources for animals, which in turn influence likelihood of arrival of wind- and animal-dispersed seeds. Quantifying the effects of an individual tree species on seed rain in a highly diverse natural forest is challenging, and thus understudied. Seed rain of very small seeds (<1 mm long) is also relatively uncharacterized because seed trap mesh size is usually ≥1 mm. In a unique experimental setting containing replicated, monodominant, 26-yr-old plantations of four native tree species at La Selva Biological Station (Costa Rica), we studied the effects of four native tree species on seed rain. We collected seed rain of woody species for 14 months in 15 50-×-50-m plots from 75 traps. In each plot three traps were lined with Terylene® fabric of 1-µm (fine) mesh and two with 1-mm (regular) mesh.

Across all traps, the total annual seed rain was 133,355 seeds from 121 ...


Quantifying The Effects Of Daily Light Integral Or Photoperiod On Maize Tassel Morphology Across Developmental Stages, Elizabeth Ann Trecker Jan 2018

Quantifying The Effects Of Daily Light Integral Or Photoperiod On Maize Tassel Morphology Across Developmental Stages, Elizabeth Ann Trecker

Graduate Theses and Dissertations

ABSTRACT

Maize (Zea mays L.) is an important agronomic crop throughout the world. Maize seed production and trait introgression is performed in both field and greenhouse settings (which allow for continual production seasons). The winter months within the greenhouses produce maize tassels with increased barren tassel branches (suppressed anther production) and the hypothesis is that the most limiting factor is daily light integral (DLI). Growing maize year-round in temperate regions, such as the northern part of the United States, requires the use-of greenhouse production. The low light intensities of these regions in the winter months creates a need for supplemental ...


Investigations Into The Function Of Common Milkweed (Asclepias Syriaca) In The Agricultural Landscape, Sydney Lizotte-Hall Jan 2018

Investigations Into The Function Of Common Milkweed (Asclepias Syriaca) In The Agricultural Landscape, Sydney Lizotte-Hall

Graduate Theses and Dissertations

The monarch butterfly’s (Danaus plexippus Linnaeus) vibrant orange color with contrasting black veins and white spots make it recognizable to many. Unfortunately, the remarkable migration made by the eastern monarch population is at risk due to the recent decline in this cohort of the species. Many factors are said to have caused the decline, including overwintering habitat destruction, increased dependence on herbicide-tolerant crops, extreme climatic events, predation, loss of breeding habitat, etc.

Two studies were conducted to: 1) determine the impact of sub-lethal herbicides on growth of common milkweed and utilization by monarchs and 2) investigate simple methods for ...


Molecular Mechanisms Governing Plant Parasitic Nematode Signaling And Host Parasitism, Stacey Nicola Barnes Jan 2018

Molecular Mechanisms Governing Plant Parasitic Nematode Signaling And Host Parasitism, Stacey Nicola Barnes

Graduate Theses and Dissertations

Pathogen infection of crops causes large-scale annual yield losses for farmers worldwide and hinders global efforts to provide adequate amounts of nutrition for the ever-growing human population. Plant-parasitic nematodes (PPN) are among some of the most devastating pathogens due to their ability to parasitize an expansive variety of agriculturally important crops. In order to identify ways to attenuate PPN infection and limit yield losses it is vital that we increase our understanding of host-PPN interactions. Here we investigate the molecular mechanisms that are occurring both within PPN and at the interface between PPN and their host plants.

Research into PPN-derived ...


Evaluating The Impacts Of Midwestern Cropping Systems On Soil Health And Subsurface Drainage Water Quality, Brian Dougherty Jan 2018

Evaluating The Impacts Of Midwestern Cropping Systems On Soil Health And Subsurface Drainage Water Quality, Brian Dougherty

Graduate Theses and Dissertations

Agricultural nutrient management practices are an important component of the effort to improve water quality in the Mississippi River Basin. In particular, there is concern about nutrient export to the Gulf of Mexico via loss from subsurface drainage systems. Optimizing the use of fertilizers and animal manures in combination with other management practices has the potential to minimize negative impacts on water quality. Farmers are increasingly challenged to maximize crop production while utilizing fertilizers and animal manures in an efficient and environmentally friendly manner. An increasing awareness of the potential to address these issues by improving soil health has also ...


A Tale Of Regulation: Analysis Of The Role Of Snrk1 And Glutathione In Autophagy In Arabidopsis Thaliana, Junmarie Soto-Burgos Jan 2018

A Tale Of Regulation: Analysis Of The Role Of Snrk1 And Glutathione In Autophagy In Arabidopsis Thaliana, Junmarie Soto-Burgos

Graduate Theses and Dissertations

Autophagy is a degradation process in which cells break down and recycle their cytoplasmic contents when subjected to environmental stress or during development. Upon activation of autophagy, a double membrane vesicle called the autophagosome forms around the cargo and delivers it to the vacuole/lysosome for degradation. In mammals, regulation of autophagy has been extensively studied. In plants, key regulators of autophagy have been identified, but their upstream components are poorly understood. This dissertation summarizes my efforts in studying the regulation of autophagy in Arabidopsis thaliana.

AMPK in animals, and its yeast homolog Snf1, are positive regulators of autophagy. The ...


Genomic Analysis Of Quantitative Disease Resistance During Maize-Hemibiotrophic Leaf Blight Pathogen Interaction, Mercy Kasuzi Kabahuma Jan 2018

Genomic Analysis Of Quantitative Disease Resistance During Maize-Hemibiotrophic Leaf Blight Pathogen Interaction, Mercy Kasuzi Kabahuma

Graduate Theses and Dissertations

Plant diseases account for more than 40% of crop losses. Breeding for disease resistance is the most effective means of crop protection against these losses. Disease resistance in plants is categorized into qualitative and quantitative resistance. Qualitative disease resistance is controlled by single major genes that confer complete or near complete resistance against disease pathogens. However, the absence or instability of qualitative resistance in many crop-pathogen interaction systems has necessitated a shift in research toward quantitative disease resistance (QDR). QDR is conditioned by several genes of minor effects resulting in reduced levels of disease. The multigenic nature of QDR overcomes ...


Using Genomic And Gene Expression Methods To Understand The Phenotypic Response Of Soybean To Sudden Death Syndrome Caused By Fusarium Virguliforme, Alexander Stephen Luckew Jan 2018

Using Genomic And Gene Expression Methods To Understand The Phenotypic Response Of Soybean To Sudden Death Syndrome Caused By Fusarium Virguliforme, Alexander Stephen Luckew

Graduate Theses and Dissertations

Soybean sudden death syndrome (SDS) is one of the most important soybean diseases in the Midwestern United States, leading to average losses of $396 million per year from 1996 to 2015. The causal agent of SDS, soilborne fungus Fusarium virguliforme (Fv), causes root rot symptoms and releases phytotoxins taken up by the plant to produce chlorosis and necrosis in the leaves. The main management practice used to reduce the impact of SDS is planting resistant soybean cultivars. Resistance to SDS is known to be quantitative with 88 known quantitative trait loci (QTL) based on Soybase.org. Many of these QTL ...


Identification And Qtl Mapping Of Physiological Drivers Of Soybean Yield Under Contrasting Management Systems Using High-Throughput Phenotyping, Race Heith Higgins Jan 2018

Identification And Qtl Mapping Of Physiological Drivers Of Soybean Yield Under Contrasting Management Systems Using High-Throughput Phenotyping, Race Heith Higgins

Graduate Theses and Dissertations

Rapid characterization of physiological traits driving yield are becoming desirable aides to breeding programs to increase the rate of genetic gain. Each chapter in this dissertation investigates areas related to high-throughput phenotyping and physiological traits driving soybean yield. Chapter two seeks to understand the response of diverse soybean germplasm to seeding rate. An evaluation of final plot seed yield, seed protein percentage, seed oil percentage, seed weight, height, maturity, and plant lodging revealed a significant genotype x seeding rate interaction only for lodging, suggesting current soybean germplasm and soybean of wide genetic ancestry respond similarly to seeding rate. Our second ...


Drivers Of Yield And Nitrogen-Loss Tradeoffs: Cropping System Evaluations With Process-Based Modeling, Rafael Alejandro Martinez-Feria Jan 2018

Drivers Of Yield And Nitrogen-Loss Tradeoffs: Cropping System Evaluations With Process-Based Modeling, Rafael Alejandro Martinez-Feria

Graduate Theses and Dissertations

The Midwest is one of the most productive agricultural regions, but mitigating loss of nitrogen (N) from cropland is needed to improve environmental quality. Tradeoffs between crop yield and N loss have been linked largely to the inefficient use of N fertilizers, but the contributions of more systemic factors such as soil characteristics, crop sequences, and genotypes have not been thoroughly studied. This dissertation examines and quantifies the impact of various genetic, environmental and management drivers of crop yield and N-loss tradeoffs in the maize and soybean cropping systems of the US Midwest, and identifies potential management strategies to lessen ...


Genetic And Brassinosteroid Control Underlying Leaf Angle Variation Across The Canopy In Sorghum, Maria Betsabe Mantilla Perez Jan 2018

Genetic And Brassinosteroid Control Underlying Leaf Angle Variation Across The Canopy In Sorghum, Maria Betsabe Mantilla Perez

Graduate Theses and Dissertations

Leaf angle, the inclination between the midrib of a leaf blade and the stem, is one of the main determinants of crop productivity. Plants with an upright leaf angle on the top and more horizontal towards the bottom can maximize their light interception and photosynthetic capacity, increasing yield per plant and unit of land. Experiments to investigate the genetic control of leaf angle have been routinely designed on the use of one or two arbitrarily selected leaves, or merged the data from multiple leaves on an average value. This approach has limited our understanding of the control of leaf angle ...


Increase Tiller Production In Switchgrass By Crispr/Cas9, Yang Liu Jan 2018

Increase Tiller Production In Switchgrass By Crispr/Cas9, Yang Liu

Graduate Theses and Dissertations

Switchgrass (Panicum virgatum) is an important bioenergy crop in United States. During past decades, numerous research studies on switchgrass breeding, genetics and biology have been conducted to improve the biomass yield of switchgrass. It has been shown that tiller number is positively correlated with biomass yield in switchgrass. To facilitate breeding improvement for tiller production, it is urgent to understand the tillering mechanism at the molecular level in switchgrass. The teosinte branched 1 (tb1) gene is a well-studied branching related gene in grasses. Yet, the function of tb1-like genes in switchgrass is still not clear. Characterizing the roles of Panicum ...


To Grow Or Survive: Plants Modulate Brassinosteroid-Regulated Transcription Factor Bes1 During Drought To Balance Growth And Stress Responses, Trevor Nolan Jan 2018

To Grow Or Survive: Plants Modulate Brassinosteroid-Regulated Transcription Factor Bes1 During Drought To Balance Growth And Stress Responses, Trevor Nolan

Graduate Theses and Dissertations

Understanding how plants balance growth and stress responses is essential to optimize crop yield in an ever-changing environment. Brassinosteroids (BRs) regulate plant growth and stress responses, including that of drought. BRs signal to control the activities of the BES1/BZR1 family transcription factors (TFs), which in turn mediate the expression of more than 5,000 BR-responsive genes. The network through which BES1 regulates the large number of target genes and the factors that modulate BES1 during stress are only beginning to be understood. In this thesis, I investigated several mechanisms that converge on BES1 to balance BR-regulated growth and stress ...


Evolutionary Histories Of Legume Genomes And Mechanisms Of Genome Remodeling, Longhui Ren Jan 2018

Evolutionary Histories Of Legume Genomes And Mechanisms Of Genome Remodeling, Longhui Ren

Graduate Theses and Dissertations

Evolutionary genomics analysis of plants aims to reveal and help us to understand the history of genome evolution that plants have undergone. So far, many specific topics and questions of genome evolution have been studied and answered. However, there are still a large number of questions to which the answers are unknown or not clear. In this dissertation, I focus on two specific topics of evolutionary genomics: (1) genome size evolution following genomic rearrangements in plants; (2) ancestral genome reconstruction in legumes.

Using a model of two wild peanut relatives in which one genome experienced large rearrangements, we find that ...


The Horticultural Potential Of Wastewater-Grown Algae Fertilizers, J Austin Gimondo Jan 2018

The Horticultural Potential Of Wastewater-Grown Algae Fertilizers, J Austin Gimondo

Graduate Theses and Dissertations

This thesis comprises five chapters and details the evaluation of wastewater-grown-algae-based materials as plant fertilizers in container-crop production. Chapter one provides context for the thesis followed by a detailed review of literature relevant to bio-based fertilization and the use of algae to treat wastewater. Chapters two through four are manuscripts intended for submission to HortScience. Chapter two details the production of three container-grown crops with pellets or pastes of wastewater-grown algae as a fertilizer source. Evaluation of extruded algae-and-bioplastic materials as fertilizers for three container-crops and for turfgrass are reported in chapters three and four, respectively. The final chapter synthesizes ...


Functions And Mechanisms Of Ap2/Erf And Myb Family Transcription Factors In Brassinosteroid-Regulated Plant Growth And Stress Responses, Zhouli Xie Jan 2018

Functions And Mechanisms Of Ap2/Erf And Myb Family Transcription Factors In Brassinosteroid-Regulated Plant Growth And Stress Responses, Zhouli Xie

Graduate Theses and Dissertations

Brassinosteroids (BRs) are a class of plant steroid hormones that play important roles in plant growth and development, as well as biotic and abiotic stress responses. BR functions through membrane receptor BRI1, co-receptor BAK1 and a cascade of signaling components to regulate BES1/BZR1 family transcription factors. Comprehensive chromatin-binding and transcriptome reveal that more than 500 transcription factors are regulated by BES1/BZR1, which supports the idea that BES1/BZR1 control multiple biological processes through diverse transcription factors. Among those transcription factors, there are two classes of typical stress responsive transcription factors: TINYs in AP2/ERF family and BOS1 in ...


Genetic And Environmental Control Of Lignin Biosynthesis And C Emission From Crop Stover, Sarah Hill-Skinner Jan 2018

Genetic And Environmental Control Of Lignin Biosynthesis And C Emission From Crop Stover, Sarah Hill-Skinner

Graduate Theses and Dissertations

Lignin is the second most abundant terrestrial biopolymer in the world and provides structural strength to plants. The maize brown midrib (bm) mutants accumulate less and altered lignin relative to non-mutants. Maize bm4-encoded folylpolyglutamate synthase functions to generate the preferred substrate of folate-dependent enzymes, such as bm2-encoded methylenetetrahydrofolate reductase. Consistent with bm4’s predicted function upstream of bm2, both mutants display a 7-10% reduction in lignin content and a 16-40% increase in S/G lignin ratio relative to wild-type. This interplay between lignin biosynthesis and various metabolic processes is also seen between lignin and stover carbon emission. As climate change ...


The Growing Together Project: Understanding Impacts On Field Day Attendees And Iowa Master Gardeners, Laura Irish Jan 2018

The Growing Together Project: Understanding Impacts On Field Day Attendees And Iowa Master Gardeners, Laura Irish

Graduate Theses and Dissertations

Citizen science has been shown to be an effective tool for increasing data collection, as well as a great benefit to those who participate in the research project. The rising costs and limited funding for conducting large-scale research projects make citizen science projects valuable assets for researchers. Understanding the impact of citizen science projects on the volunteers must be done to better engage with and retain the volunteers. The Growing Together project, a partnership between the ISU Extension and Outreach Master Gardener program and the Human Sciences Extension, was created to increase food security in Iowa. The two major components ...


The Influence Of Multiple Herbicide Resistance On Growth And Development Of Amaranthus Tuberculatus And The Efficacy Of The Very Long Chain Fatty Acid-Inhibiting Herbicides On Multiple Herbicide-Resistant Amaranthus Tuberculatus; Investigating A Putative 4-Hydroxylphenylpyruvate Dioxygenase-Inhibiti, Eric Alexander Lyle Jones Jan 2018

The Influence Of Multiple Herbicide Resistance On Growth And Development Of Amaranthus Tuberculatus And The Efficacy Of The Very Long Chain Fatty Acid-Inhibiting Herbicides On Multiple Herbicide-Resistant Amaranthus Tuberculatus; Investigating A Putative 4-Hydroxylphenylpyruvate Dioxygenase-Inhibiti, Eric Alexander Lyle Jones

Graduate Theses and Dissertations

Iowa farmers rely mainly on herbicides for weed management. Inconsistent and unsatisfactory weed control is being realized as the spread of herbicide-resistant weed populations has increased. Populations of waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer) and giant ragweed (Ambrosia trifida L.) have evolved resistance to glyphosate and other herbicides commonly used in crop fields. This research focuses on the growth and development of multiple herbicide-resistant waterhemp and assessing the evolution of new herbicide-resistant waterhemp and giant ragweed populations.

Significant differences in growth, flowering, accumulated biomass, and seed production were detected when the multiple herbicide-resistant waterhemp populations were compared to a ...