Plant Biology Commons^™

Training Future Agriculture Professionals In Landowner–Tenant Conservation Decision-Making, Andrea Basche, Angie Carter

Department of Agronomy and Horticulture: Faculty Publications

The landowner–tenant relationship is important to the implementation of conser- vation on agricultural lands. Women own or co-own a significant portion of U.S. farmland yet are underrepresented in conservation research. The next generation of agriculture professionals can benefit from first-hand experience in assisting women landowners and their tenants in navigating the complexities of conser- vation decision-making. This article analyzes undergraduate student perceptions of landowner–tenant relationships in conservation management through their engagement in case studies with women landowner–tenant pairs in the Western Corn Belt. Student groups were asked to complete a management improvement plan that both incorporated the agronomic and conservation …

Winter Cover Crop Root Biomass Yield In Corn And Soybean Systems, Sabrina J. Ruis, Humberto Blanco-Canqui, Katja Koehler-Cole, Paul J. Jasa, G. Slater, Roger W. Elmore, Richard B. Ferguson

Department of Agronomy and Horticulture: Faculty Publications

Cover crop (CC) roots are critical for soil ecosystem service delivery including soil stabilization, C and nutrient cycling, soil health improvement, and others. However, most CC studies only evaluate CC aboveground biomass yield, neglecting the belowground portion of the plant. The objectives of this study were to quantify the impacts of (a) CC planting (pre- and post-harvest) dates and (b) early (2–4 wk before main crop planting) and late (at main crop planting) CC termination with and without corn (Zea mays L.) residue removal on root biomass yield. We assessed the effects of CC planting or termination dates on root …

Floral Trait Architecture In Crop Sunflower (Helianthus Annuus) Under Drought Conditions, Lauren Segarra

All Master's Theses

Longer and more intense droughts are predicted to become more common in the coming century due to anthropogenic climate change. Drought can reduce crop yield and decrease food security. In order to mitigate the negative effects of drought on crop production, it is important to elucidate the underlying mechanisms that promote drought stress resistance in crop plants. Floral traits impact yield, especially in oilseed crops such as sunflower (Helianthus annuus), but their susceptibility to drought stress is understudied. The goal of this study was to describe the floral trait architecture of H. annuus crop lines under drought versus …

Principles, Applications, And Biosafety Of Plant Genome Editing Using Crispr-Cas9, Kaoutar El-Mounadi, María Luisa Morales-Floriano, Hernan Garcia-Ruiz

Department of Plant Pathology: Faculty Publications

The terms genome engineering, genome editing, and gene editing, refer to modifications (insertions, deletions, substitutions) in the genome of a living organism. The most widely used approach to genome editing nowadays is based on Clustered Regularly Interspaced Short Palindromic Repeats and associated protein 9 (CRISPR-Cas9). In prokaryotes, CRISPR-Cas9 is an adaptive immune system that naturally protects cells from DNA virus infections. CRISPR-Cas9 has been modified to create a versatile genome editing technology that has a wide diversity of applications in medicine, agriculture, and basic studies of gene functions. CRISPR-Cas9 has been used in a growing number of monocot and dicot …

The Limits Of Lead (Pb) Phytoextraction And Possibilities Of Phytostabilization In Contaminated Soil: A Critical Review, Sara Perl Egendorf, Peter M. Groffman, Gerry Moore, Zhongqi Cheng

Advanced Science Research Center

This review article focuses on lead (Pb), one of the most ubiquitous and harmful toxicants found in soil. Our objective is to address misconceptions regarding the ability of plants to uptake Pb through their roots and translocate it to above-ground tissues, and their ability to act as hyperaccumulators and thereby phytoextract Pb. In accordance with a number of cited definitions, we suggest that species capable of Pb phytoextraction can be rated with the following three criteria: (1) root uptake above a nominal threshold of 1,000 mg Pb/kg, (2) bioconcentration factor (BCF or shoot/soil concentration) >1, and (3) translocation factor (TF …

Trees, Fungi, Insects: How Host Plant Genetics Builds A Community, Sandra Jeanne Simon

Graduate Theses, Dissertations, and Problem Reports (ETD)

Organisms, such as fungi and insects, can cause millions of acres of agricultural and forest damage, while others provide billions of dollars in ecological services such as education, aesthetic enjoyment, pollination, and gardening. Plant breeding and biotechnology can potentially help establish a balance between the proliferation of detrimental pests and attraction of beneficial insects. Variation in plant physiological and morphological characteristics are extremely important in the ability of host tissues to support many different types of organisms. When that variation is genetically heritable in a plant population, shifts in the underlying genes can have predictable consequences in structuring entire ecosystems. …

The Morphological, Physiological, And Genetic Underpinnings Of Intraspecific Salinity Tolerance In Sorghum Bicolor, Ashley N. Henderson

Graduate Theses, Dissertations, and Problem Reports (ETD)

Decreases in land quality and quantity threaten the efficient production of agriculturally and economically pivotal crops. Such reductions in arable lands are a consequence of population growth and urbanization, and often result in the introduction of various abiotic stresses. The most common abiotic stressors include water limitation (drought), water logging (over watering), poor water quality (salinity), and extreme temperatures (cold, frost, heat). Each of these stressors negatively impact plant growth, development, and yield. Soil salinity, specifically, is a considerable constraint affecting lands used in agriculture. Salts in the soil rise both naturally and through anthropogenic factors making the abundance a …

Variation Profile Of The Orthotospovirus Genome, Deepti Nigam, Hernan Garcia Ruiz

Department of Plant Pathology: Faculty Publications

Orthotospoviruses are plant-infecting members of the family Tospoviridae (order Bunyavirales), have a broad host range and are vectored by polyphagous thrips in a circulative- propagative manner. Because diverse hosts and vectors impose heterogeneous selection constraints on viral genomes, the evolutionary arms races between hosts and their pathogens might be manifested as selection for rapid changes in key genes. These observations suggest that orthotospoviruses contain key genetic components that rapidly mutate to mediate host adaptation and vector transmission. Using complete genome sequences, we profiled genomic variation in orthotospoviruses. Results show that the three genomic segments contain hypervariable areas at homologous locations …

Wheat Growth Monitoring And Yield Estimation Based On Multi-Rotor Unmanned Aerial Vehicle, Zhaopeng Fu, Jie Jang, Yang Gao, Brian Krienke, Meng Wang, Kaitai Zhong, Qiang Cao, Yongchao Tian, Yan Zhu, Weixing Cao, Xiaojun Liu

Department of Agronomy and Horticulture: Faculty Publications

Leaf area index (LAI) and leaf dry matter (LDM) are important indices of crop growth. Real-time, nondestructive monitoring of crop growth is instructive for the diagnosis of crop growth and prediction of grain yield. Unmanned aerial vehicle (UAV)-based remote sensing is widely used in precision agriculture due to its unique advantages in flexibility and resolution. This study was carried out on wheat trials treated with different nitrogen levels and seeding densities in three regions of Jiangsu Province in 2018–2019. Canopy spectral images were collected by the UAV equipped with a multi-spectral camera during key wheat growth stages. To verify the …

The State Of Sustainable Agriculture And Agroecology Research And Impacts: A Survey Of U.S. Scientists, Marcia Delonge, Tali Robbins, Andrea D. Basche, Lindsey Haynes-Maslow

Department of Agronomy and Horticulture: Faculty Publications

A growing body of research suggests that although sustainable agriculture, particularly agroecology, can address challenges such as those related to climate change, ecosystem services, food insecurity, and farmer livelihoods, the transition to such systems remains limited. To gain insight into the state of U.S. sustainable agriculture and agroecology, we developed a 28-question mixed-method survey that was administered to scientists in these fields. Respondents (N=168) represented diverse locations, institutions, and career stages. They offered varied definitions of sustainable agriculture, with 40% considering economic and social well-being to be core components. Respondents identified the amount and duration of public research …

Gwas: Fast-Forwarding Gene Identification And Characterization In Temperate Cereals: Lessons From Barley – A Review, Ahmad M. Alqudah, Ahmed Sallam, P. Stephen Baenziger, Andreas Börner

Department of Agronomy and Horticulture: Faculty Publications

Understanding the genetic complexity of traits is an important objective of small grain temperate cereals yield and adaptation improvements. Bi-parental quantitative trait loci (QTL) linkage mapping is a pow- erful method to identify genetic regions that co-segregate in the trait of interest within the research pop- ulation. However, recently, association or linkage disequilibrium (LD) mapping using a genome-wide association study (GWAS) became an approach for unraveling the molecular genetic basis underlying the natural phenotypic variation. Many causative allele(s)/loci have been identified using the power of this approach which had not been detected in QTL mapping populations. In barley (Hordeum …

Benchmarking Impact Of Nitrogen Inputs On Grain Yield And Environmental Performance Of Producer Fields In The Western Us Corn Belt, Fatima A.M. Tenorio, Eileen L. Mclellan, Alison J. Eagle, Kenneth G. Cassman, Daryl Andersen, Marie Krausnick, Russell Oaklund, John Thorburn, Patricio Grassini

Department of Agronomy and Horticulture: Faculty Publications

Benchmarking crop yields against nitrogen (N) input levels can help provide opportunities to improve N ferti-lizer efficiency and reduce N losses on maize in the US Corn Belt by identifying fields most likely to benefit from improved N management practices. Here, we evaluated a large producer database that includes field-level data on yield and applied N inputs from 9280 irrigated and rainfed fields over a 7-year period (2009–2015) in Nebraska (USA). A spatial framework, based on technology extrapolation domains, was used to cluster each field into spatial units with similar climate and soil type that represent 1.3 million ha of …

Soil Sample Timing, Nitrogen Fertilization, And Incubation Length Influence Anaerobic Potentially Mineralizable Nitrogen, Jason Clark, Kristen S. Veum, Fabián G. Fernández, Newell R. Kitchen, James J. Camberato, Paul Carter, Richard Ferguson, David W. Franzen, Daniel E. Kaiser, Carrie A. M. Laboski, Emerson Nafziger, Carl J. Rosen, John E. Sawyer, John F. Shanahan

Department of Agronomy and Horticulture: Faculty Publications

Understanding the variables that affect the anaerobic potentially mineralizable N (PMNan) test should lead to a standard procedure of sample collection and incubation length, improving PMNan as a tool in corn (Zea mays L.) N management. We evaluated the effect of soil sample timing (preplant and V5 corn development stage [V5]), N fertilization (0 and 180 kg ha−1) and incubation length (7, 14, and 28 d) on PMNan (0–30 cm) across a range of soil properties and weather conditions. Soil sample timing, N fertilization, and incubation length affected PMNan differently based on soil and weather conditions. Preplant vs. V5 PMNan …

Quantifying On‐Farm Nitrous Oxide Emission Reductions In Food Supply Chains, A.J. Eagle, E. Mclellan, E.M. Brawner, M.H. Chantigny, Eric A. Davidson, J.B. Dickey, Bruce A. Linquist, T.M. Maaz, D.E. Pelster, Cameron M. Pittelkow, C. Van Kessel, T.J. Vyn, K. G. Cassman

Department of Agronomy and Horticulture: Faculty Publications

Reducing nitrous oxide (N2O) emissions from agriculture is critical to limiting future global warming. In response, a growing number of food retailers and manufacturers have committed to reducing N2O emissions from their vast networks of farmer suppliers by providing technical assistance and financial incentives. A key challenge for such companies is demonstrating that their efforts are leading to meaningful progress toward their climate mitigation commitments. We show that a simplified version of soil surface nitrogen (N) balance—or partial N balance—the difference between N inputs to and outputs

from a farm field (fertilizer N minus crop N), is a robust indicator …

Cover Crops And Weed Suppression In The U.S. Midwest: A Meta-Analysis And Modeling Study, Virginia Nicholas, Rafael Martinez-Feria, David Weisberger, Sarah Carlson, B. Basso, Andrea Basche

Department of Agronomy and Horticulture: Faculty Publications

In addition to soil health and conservation benefits, cover crops (CCs) may offer weed control in the midwestern United States, but individual studies report vary- ing effects. We conducted a meta-analysis of studies measuring weed biomass (WBIO) or density (WDEN) in paired CC and no-cover treatments in corn (Zea mays L.)–soybean [Glycine max (L.) Merr] rotations in the U.S. Midwest. Fifteen studies provided 123 paired comparisons of WBIO and 119 of WDEN. Only grass CCs significantly reduced WBIO, while no CC reduced WDEN. We found no evidence CC management factors (e.g., termination method) directly affected out- comes. Our dataset showed …

Woody Plant Encroachment And The Sustainability Of Priority Conservation Areas, Dillon Fogarty, Caleb P. Roberts, Daniel R. Uden, Victoria M. Donovan, Craig R. Allen, David E. Naugle, Matthew O. Jones, Brady W. Allred, Dirac L. Twidwell Jr

Department of Agronomy and Horticulture: Faculty Publications

Woody encroachment is a global driver of grassland loss and management to counteract encroachment represents one of the most expensive conservation practices implemented in grasslands. Yet, outcomes of these practices are often unknown at large scales and this constrains practitioner’s ability to advance conservation. Here, we use new monitoring data to evaluate outcomes of grassland conservation on woody encroachment for Nebraska’s State Wildlife Action Plan, a statewide effort that targets management in Biologically Unique Landscapes (BULs) to conserve the state’s natural communities. We tracked woody cover trajectories for BULs and compared BUL trajectories with those in non-priority landscapes (non-BULs) to …

Is Allelopathy From Winter Cover Crops Affecting Row Crops?, Katja Koehler-Cole, Sydney Everhart, Yan Gu, Christopher A. Proctor, Margarita Marroquin-Guzman, Daren Redfearn, Roger W. Elmore

Department of Agronomy and Horticulture: Faculty Publications

Cover crops (CC) have been explored in corn (Zea mays L.), cotton (Gossypium hirsutum L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) systems for their allelopathic potential to control weeds. However, allelopathic compounds may negatively affect these row crops by reducing germination, emergence, and grain yields. We reviewed studies that document allelopathic effects of CC on subsequent row crops in field and laboratory settings. We summarize the influence of CC management, including biomass production, planting and termination timing on allelochemical quantity. Our review found few studies documenting allelopathic effects of CC on row …

Soil Aggregation As Affected By Application Of Diverse Organic Materials, Maman Garba, Charles S. Wortmann, Humberto Blanco-Canqui

Department of Agronomy and Horticulture: Faculty Publications

Application of organic materials can amend soil for improved water infiltration and reduced erodibility with effects varying with soil properties and the organic amendment type and rate. The effects of four livestock manures, three municipal biosolids, and one industrial by-product on dry and wet soil aggregate stability were evaluated at six sites in Nebraska. The amendments had similar C/N ratios but the biosolids had relatively high concentrations of lignin and cellulose. Soil organic matter (SOM) ranged from 21 to 65 g kg−1 and soils were silty clay loam, silt loam, or loamy sand. Soil was sampled for the 0- to …

Strategic Switchgrass (Panicum Virgatum) Production Within Row Cropping Systems: Regional-Scale Assessment Of Soil Erosion Loss And Water Runoff Impacts, Enheng Wang, R. M. Cruse, Bharat Sharma-Acharya, Daryl E. Herzmann, Brian K. Gelder, David E. James, Dennis C. Flanagan, Humberto Blanco-Canqui, Robert B. Mitchell, David Laird

Department of Agronomy and Horticulture: Faculty Publications

A strong need exists for tools to assess the efficacy of conservation practices across large regions supporting informed policy decisions that may lead to better soil and water conservation while optimizing agricultural production options. Perennial warm-season grasses (WSGs) such as switchgrass (Panicum virgatum), can be grown on marginally productive and/or environmentally sensitive lands to meet growing bioenergy demands while reducing water runoff and soil erosion compared to current row crop systems. Quantifying the soil and water conservation effects of WSG when strategically placed on the landscape would help support decisions favoring both economic and environmental benefits. We used the Daily …

The Lateral Root Density Gene Regulates Root Growth During Water Stress In Wheat, Dante F. Placido, Jaspreet Sandhu, Shirley Sato, Natalya Nersesian, Truyen Quach, Thomas Clemente, Paul Staswick, Harkamal Walia

Department of Agronomy and Horticulture: Faculty Publications

Drought stress is the major limiting factor in agriculture. Wheat, which is the most widely grown crop in the world, is predominantly cultivated in drought-prone rainfed environments. Since roots play a critical role in water uptake, root response to water limitations is an important component for enhancing wheat adaptation. In an effort to discover novel genetic sources for improving wheat adaptation, we characterized a wheat translocation line with a chromosomal segment from Agropyron elongatum, a wild relative of wheat, which unlike common wheat maintains root growth under limited-water conditions. By exploring the root transcriptome data, we found that reduced …

Allelic Variation In Rice Fertilization Independent Endosperm 1 Contributes To Grain Width Under High Night Temperature Stress, Balpreet K. Dhatt, Puneet Paul, Jaspreet Sandhu, Waseem Hussain, Larissa Irvin, Feiyu Zhu, Maria Arlene Adviento-Borbe, Argelia Lorence, Paul Staswick, Hongfeng Yu, Gota Morota, Harkamal Walia

Department of Agronomy and Horticulture: Faculty Publications

A higher minimum (night-time) temperature is considered a greater limiting factor for reduced rice yield than a similar increase in maximum (daytime) temperature. While the physiological impact of high night temperature (HNT) has been studied, the genetic and molecular basis of HNT stress response remains unexplored.

We examined the phenotypic variation for mature grain size (length and width) in a diverse set of rice accessions under HNT stress. Genome-wide association analysis identified several HNT-specific loci regulating grain size as well as loci that are common for optimal and HNT stress conditions.

A novel locus contributing to grain width under HNT …

Leveraging Genome-Enabled Growth Models To Study Shoot Growth Responses To Water Deficit In Rice, Malachy T. Campbell, Alexandre Grondin, Harkamal Walia, Gota Morota

Department of Agronomy and Horticulture: Faculty Publications

lucidating genotype-by-environment interactions and partitioning its contribution to phenotypic variation remains a challenge for plant scientists. We propose a framework that utilizes genome-wide markers to model genotype-specific shoot growth trajectories as a function of time and soil water availability. A rice diversity panel was phenotyped daily for 21 d using an automated, high-throughput image-based, phenotyping platform that enabled estimation of daily shoot biomass and soil water content. Using these data, we modeled shoot growth as a function of time and soil water content, and were able to determine the time point where an inflection in the growth trajectory occurred. We …

Voxel Carving-Based 3d Reconstruction Of Sorghum Identifies Genetic Determinants Of Light Interception Efficiency, Mathieu Gaillard, Chenyong Miao, James Schnable, Bedrich Benes

Department of Agronomy and Horticulture: Faculty Publications

Changes in canopy architecture traits have been shown to contribute to yield increases. Optimizing both light interception and light interception efficiency of agricultural crop canopies will be essential to meeting the growing food needs. Canopy architecture is inherently three-dimensional (3D), but many approaches to measuring canopy architecture component traits treat the canopy as a two-dimensional (2D) structure to make large scale measurement, selective breeding, and gene identification logistically feasible. We develop a high throughput voxel carving strategy to reconstruct 3D representations of sorghum from a small number of RGB photos. Our approach builds on the voxel carving algorithm to allow …

Genome-Wide Identification And Analysis Of Heterotic Loci In Three Maize Hybrids, Hongjun Liu, Qin Wang, Mengjiao Chen, Yahui Ding, Xuerong Yang, Jie Liu, Xiaohan Li, Congcong Zhou, Qilin Tian, Yiqi Lu, Danlin Fan, Junpeng Shi, Lin Zhang, Congbin Kang, Mingfei Mingfei Sun, Fangyuan Li, Yujian Wu, Yongzhong Zhang, Baoshen Liu, Xiang Yu Zhao, Qi Feng, Jinliang Yang, Bin Han, Jinsheng Lai, Xian Sheng Zhang, Xuehui Huang

Department of Agronomy and Horticulture: Faculty Publications

Heterosis, or hybrid vigour, is a predominant phenomenon in plant genetics, serving as the basis of crop hybrid breeding, but the causative loci and genes underlying heterosis remain unclear in many crops. Here, we present a large-scale genetic analysis using 5360 offsprings from three elite maize hybrids, which identifies 628 loci underlying 19 yield-related traits with relatively high mapping resolutions. Heterotic pattern investigations of the 628 loci show that numerous loci, mostly with complete–incomplete dominance (the major one) or overdominance effects (the secondary one) for heterozygous genotypes and nearly equal proportion of advantageous alleles from both parental lines, are the …

The Balancing Act Of Cytokinin In Environmental Stress Tolerance, Sumudu Sandeepani Karunadasa

Theses and Dissertations--Plant and Soil Sciences

Cytokinin, long known as a phytohormone that regulates plant growth and development, has been recently recognized as an important regulator of stress responses. However, our current knowledge about the mechanisms by which cytokinin regulates stress responses is fragmentary, as many of the studies in this field yielded conflicting results. Most of the work described here has focused on analyses of the molecular mechanisms of cytokinin-dependent regulation of growth and development under stress conditions, with an emphasis on the role of cytokinin-dependent regulation of protein synthesis in development and stress tolerance.

One of the important contributions of this study is the …

Stimulated Growth Response To Sand Burial Of A Coastal Shrub, D. Nicole Keller

Theses and Dissertations

Drivers of vegetation zonation on barrier islands are complex and interconnected. Sand burial is a strong driver in dynamic coastal systems, especially in the foredune community. However, it is not well understood how burial impacts the interdunal swales communities and it is especially difficult to separate the effects of burial from salinity. Climate change is altering the frequency of overwash events as well as expanding the range of the native shrub, Morella cerifera, on the Virginia barrier islands. To accurately forecast island response to climate change it is important to understand how the shrub responds to sand burial. Juvenile …

Phenology Of Cupressaceae Urban Infrastructure Related To Its Pollen Content And Meteorological Variables, A. Monroy-Colín, J. M. Maya-Manzano, I. Silva-Palacios, R. Tormo-Molina, R. Pecero-Casimiro, Á. Gonzalo-Garijo, S. Fernández-Rodríguez

Articles

Cupressaceae pollen is one of the major airborne allergens of the Mediterranean region and in other regions around the world. Pollen production of these species causes considerable allergic problems during winter, being this type of pollen the most abundant in this period of the year. This work aims to relate phenology, meteorology and airborne pollen records in these species. Aerobiological sampling was carried out in Badajoz (SW Spain) from 2016 to 2018 using Hirst-type volumetric sampler. Pollination phenology was studied in 50 specimens, ten of Cupressus macrocarpa, ten of Cupressus arizonica, 15 of Cupressus sempervirens and 15 of …

The Development Of Crassulacean Acid Metabolism (Cam) Photosynthesis In Cotyledons Of The C4 Species, Portulaca Grandiflora (Portulacaceae), Lonnie J. Guralnick, Kate E. Gilbert, Diana Denio, Nicholas Antico

Arts & Sciences Faculty Publications

Portulaca grandiflora simultaneously utilizes both the C₄ and Crassulacean acid metabolism (CAM) photosynthetic pathways. Our goal was to determine whether CAM developed and was functional simultaneously with the C₄ pathway in cotyledons of P. grandiflora. We studied during development whether CAM would be induced with water stress by monitoring the enzyme activity, leaf structure, JO₂ (rate of O₂ evolution calculated by fluorescence analysis), and the changes in titratable acidity of 10 and 25 days old cotyledons. In the 10 days old cotyledons, C₄ and CAM anatomy were evident within the leaf tissue. The cotyledons showed …

Semi-Supervised Adversarial Domain Adaptation For Seagrass Detection Using Multispectral Images In Coastal Areas, Kazi Aminul Islam, Victoria Hill, Blake Schaeffer, Richard Zimmerman, Jiang Li

Electrical & Computer Engineering Faculty Publications

Seagrass form the basis for critically important marine ecosystems. Previously, we implemented a deep convolutional neural network (CNN) model to detect seagrass in multispectral satellite images of three coastal habitats in northern Florida. However, a deep CNN model trained at one location usually does not generalize to other locations due to data distribution shifts. In this paper, we developed a semi-supervised domain adaptation method to generalize a trained deep CNN model to other locations for seagrass detection. First, we utilized a generative adversarial network loss to align marginal data distribution between source domain and target domain using unlabeled data from …

Mutations In Virus-Derived Small Rnas, Deepti Nigam, Katherine Latourrette, Hernan Garcia Ruiz

Department of Plant Pathology: Faculty Publications

RNA viruses exist as populations of genome variants. Virus-infected plants accumulate 21–24 nucleotide small interfering RnAs (siRnAs) derived from viral RnA (virus-derived siRnAs) through gene silencing. This paper describes the profile of mutations in virus-derived siRNAs for three members of the family Potyviridae: Turnip mosaic virus (tuMV), Papaya ringspot virus (pRSV) and Wheat streak mosaic virus (WSMV). for tuMV in Arabidopsis thaliana, profiles were obtained for mechanically inoculated rosette leaves and systemically infected cauline leaves and inflorescence. Results are consistent withselection pressure on the viral genome imposed by local and systemic movement. By genetically removing gene silencing in the plant …