Plant Science & Landscape Architecture

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A Comparison of Irrigation-Water Containment Methods and Management Strategies Between Two Ornamental Production Systems to Minimize Water Security Threats
(MDPI, 2019-12-03) Ristvey, Andrew G.; Belayneh, Bruk E.; Lea-Cox, John D.
Water security in ornamental plant production systems is vital for maintaining profitability. Expensive, complicated, or potentially dangerous treatment systems, together with skilled labor, is often necessary to ensure water quality and plant health. Two contrasting commercial ornamental crop production systems in a mesic region are compared, providing insight into the various strategies employed using irrigation-water containment and treatment systems. The first is a greenhouse/outdoor container operation which grows annual ornamental plants throughout the year using irrigation booms, drip emitters, and/or ebb and flow systems depending on the crop, container size, and/or stage of growth. The operation contains and recycles 50–75% of applied water through a system of underground cisterns, using a recycling reservoir and a newly constructed 0.25 ha slow-sand filtration (SSF) unit. Groundwater provides additional water when needed. Water quantity is not a problem in this operation, but disease and water quality issues, including agrochemicals, are of potential concern. The second is a perennial-plant nursery which propagates cuttings and produces field-grown trees and containerized plants. It has a series of containment/recycling reservoirs that capture rainwater and irrigation return water, together with wells of limited output. Water quantity is a more important issue for this nursery, but poor water quality has had some negative economic effects. Irrigation return water is filtered and sanitized with chlorine gas before being applied to plants via overhead and micro-irrigation systems. The agrochemical paclobutrazol was monitored for one year in the first operation and plant pathogens were qualified and quantified over two seasons for both production systems. The two operations employ very different water treatment systems based on their access to water, growing methods, land topography, and capital investment. Each operation has experienced different water quantity and quality vulnerabilities, and has addressed these threats using a variety of technologies and management techniques to reduce their impacts.
Acclimation and Compensating Metabolite Responses to UV-B Radiation in Natural and Transgenic Populus spp. Defective in Lignin Biosynthesis
(MDPI, 2022-08-20) Wong, Tiffany M.; Sullivan, Joe H.; Eisenstein, Edward
Plants have evolved to protect leaf mesophyll tissue from damage caused by UV-B radiation by producing an array of UV-absorbing secondary metabolites. Flavonoids (phenolic glycosides) and sinapate esters (hydroxycinnamates) have been implicated as UV-B protective compounds because of the accumulation in the leaf epidermis and the strong absorption in the wavelengths corresponding to UV. Environmental adaptations by plants also generate a suite of responses for protection against damage caused by UV-B radiation, with plants from high elevations or low latitudes generally displaying greater adaptation or tolerance to UV-B radiation. In an effort to explore the relationships between plant lignin levels and composition, the origin of growth elevation, and the hierarchical synthesis of UV-screening compounds, a collection of natural variants as well as transgenic Populus spp. were examined for sensitivity or acclimation to UV-B radiation under greenhouse and laboratory conditions. Noninvasive, ecophysiological measurements using epidermal transmittance and chlorophyll fluorescence as well as metabolite measurements using UPLC-MS generally revealed that the synthesis of anthocyanins, flavonoids, and lignin precursors are increased in Populus upon moderate to high UV-B treatment. However, poplar plants with genetic modifications that affect lignin biosynthesis, or natural variants with altered lignin levels and compositions, displayed complex changes in phenylpropanoid metabolites. A balance between elevated metabolic precursors to protective phenylpropanoids and increased biosynthesis of these anthocyanins, flavonoids, and lignin is proposed to play a role in the acclimation of Populus to UV-B radiation and may provide a useful tool in engineering plants as improved bioenergy feedstocks.
Activating a 60's Modernist Plaza Using the Principles of Human Scale Design: Re-imagining HUD Plaza
(2021) Velez-Lopez, Sebastian; Sullivan, Jack; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Population growth has increased rapidly across many large American cities in the last 20 years. The growing population generates a need for quality public open space, but it also increases the development of housing making land increase drastically in value, making it harder for municipalities to acquire land for public open space projects. One strategy that cities can use to address this issue, is to leverage existing public spaces that are currently underutilized. This project explores the contemporary principles of public space and human scale design through a review of the existing literature. The principles gathered from the literature, are demonstrated by using them as the basis for re-imagining an underutilized urban public space. The project establishes a link between the research on public space design and practice, providing an example of how it can be used to create innovative ways to better utilize our existing public spaces.
Addressing New Stormwater Policies in the Redesign of the National Grove of State Trees at the United States National Arboretum
(2012) Kreiseder, Kory Anne; Myers, David N; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The National Grove of State Trees at the United States National Arboretum is in need of redesign to meet ecological and social needs. The Grove serves as a scientific and cultural landscape and can be repurposed to serve the public as an ecological demonstration for contemporary environmental issues. In an intensive effort to clean up the local rivers of the District of Columbia and the Chesapeake Bay, the two agencies of the District Department of the Environment and DC Water have enacted stormwater runoff fees, based on impervious surface fees, on all property owners located in the District of Columbia. The redesign of the Grove is compounded by the Arboretum's need to add more parking to the area where the Grove is currently located. The objective of this thesis is to reimagine the design and interpretation of the Grove as well as address the impervious area charge assessments.
After the Flood: Designing Land Reuse in New York's Hudson Valley
(2022) Savio, Hannah L; Ellis, Christopher D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Flooding is a recurring event in the water cycle that has the potential to devastate what is in its path. Climate change is projected to make flooding worse in the Northeastern United States because of increased intensity of rainfall. An increase in the number of flooded homes where homeowners choose not to rebuild in place can be viewed as a symptom of climate change. These issues take place at the confluence of land and water, the balance of humans and our environment, and what can be learned from the past and from projections and models of the future. How can flooded sites that are not suitable for rebuilding be adaptively reused to leverage their ecological, social, and economic value? This question is assessed through a multi-scalar examination of a series of FEMA buyouts along the Kaaterskill Creek, a rural tributary to the Hudson River in New York.
Agricultural Drainage Ditches: Soils and Implications for Phosphorus Transport and Retention
(2005-12-13) Vaughan, Robert Edward; Needelman, Brian A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Agricultural drainage ditches act as pathways for nutrients to local surface waters. Knowledge of ditch materials, the spatial variation and distribution of ditch soil phosphorus, is critical to effective ditch nutrient management strategies. Ditch materials from the University of Maryland Eastern Shore Research Farm in Princess Anne, Maryland were described and characterized using a pedological approach. The spatial variation of phosphorus was also investigated. The materials found within these ditches are natural soil bodies. Pedogenic processes operating in these soils include organic matter accumulation, structure formation, Fe oxidation and reduction, sulfuricization, sulfidization, and bioturbation. Soil phosphorus was well autocorrelated, and exhibited a high degree of spatial variation. Ditch soil phosphorus at depth ranged from 4 to 4882 mg kg-1 for total phosphorus, 4 to 4631 mg kg-1 for oxalate-extractable phosphorus, and 2 to 401 mg kg-1 for Mehlich-3 phosphorus. Future ditch management strategies should include a subsurface soils component.
Alleviation of Soil Compaction by Brassica Cover Crops
(2009) Chen, Guihua; Weil, Ray R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Soil compaction is a worldwide problem in modern agriculture associated with overuse of heavy machinery and intensification of cropping systems. Though tillage is traditionally used to alleviate compaction effect, increasing concerns about environmental impacts of tillage have led to interest in conservational tillage systems and incorporation of cover crops into crop rotations. Previous study showed soybean (Glycine Max L.) roots grew through a plowpan soil using channels left by canola (Brassica napus) cover crop roots, a process termed "biodrilling" to alleviate compaction effect. However, this study did not provide any quantitative data to support the observational conclusion. We studied "biodrilling" abilities of three cover crops and the effects of "biodrilling" on corn (Zea mays)/soybean growth by conducting three experiments. The first two experiments included three surface horizon compaction treatments (high, medium and no compaction), four cover crops [FR (forage radish: Raphanus sativus var. longipinnatus, cultivar `Daikon') and rape (rapeseed: Brassica napus, cultivar `Essex') (tap-rooted species in the Brassica family), rye (cereal rye: Secale cereale L., cultivar `Wheeler') (fibrous-rooted species) and NC (no cover crop)] in Exp. 1, and three cover crops (FR, rape and NC) in Exp. 2. The third experiment was conducted on field with a legacy plowpan (subsoil compaction) using FR, rye and NC cover crops. Roots of FR were least inhibited by compaction, while rye roots were severely arrested by compaction. The order of "biodrilling" ability was FR > rape > rye. Soil bulk density, strength and least limiting water range were controlled by compaction treatments. Soil air permeability was greatly reduced by compaction. Air permeability was greater in rape/FR treatments than in rye/NC treatments under high/medium compaction. Corn/soybean root penetrations, subsoil water uptake in the compacted soils were enhanced by FR/rape treatments but not by rye/NC treatments. Compaction decreased corn yield only in Exp. 2 where soil sand fraction was greater. The yield of corn was greater in three cover crop treatments than in NC control. In terms of "biodrilling", Brassica cover crops (FR and rape) were more effective than rye cover crop, would alleviate effects of soil compaction on plant growth in no-till farming systems.
Anacostia: Community As Form
(2014) Mendoza, Adriana; Cook, Kelly D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The essence of this thesis is to explore what form public art takes on in order to visualize Anacostia's community identity during the urban revitalization of the neighborhood. The current small and large-scale revitalization efforts by the City (Washington D.C.) are showing change in both the physical and social fabric of the community and neighborhood. As a predominantly African American community that has faced disinvestment and injustices--socially, economically, and politically--many residents are concerned that these City efforts will physically displace them, as well as the collective memory of the community. This thesis seeks to transform a vacant lot, slated for development, into a temporary, transient, multi-functional public art design for engaging the community in the process of exploration and expression of their community identity. Public art is used as a strategy to provide a platform for residents to effectively become present, visible and audible at a time when many residents feel as though they are not part of Anacostia's future.
ANALYSIS OF ARABIDOPSIS ABCB AUXIN TRANSPORTER MUTANTS REVEALS A PRIMARY ROLE IN MEMBRANE EXCLUSION
(2018) Jenness, Mark Kubo; Murphy, Angus; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Polar transport of the phytohormone auxin regulates multiple of aspects of plant growth and development. A subset of plant ATP-binding cassette subfamily B (ABCB) transporters mediate cellular auxin export. Loss of these transporters results in reduced polar auxin movement and altered plant architecture but no significant defects in embryogenesis or organ formation. Several of lines of evidence suggest that isotropically-localized ABCB transporters mediate auxin exclusion from the plasma membrane and prevention of reuptake after directional PIN-mediated efflux. Examination of the Arabidopsis auxin transporters ABCB1 and ABCB19 indicates a primary role in exclusion from small auxin producing cells in apical regions and prevention of leakage from polar auxin transport streams. Analysis of abcb mutants identifies a contribution from ABCB21 in restricting auxin to within the root vasculature in seedlings. In mature tissues, ABCB6, ABCB21, and ABCB11 make additional contributions to polar auxin transport in inflorescence stems, leaves, and flowers, respectively. The results presented herein reflect an evolutionarily conserved function for ABCB transporters in maintaining polar transport streams and prevention of cellular reuptake via exclusion.
Apple skin patterning is associated with differential expression of MYB10
(2011-05-20) Telias, Adriana; Lin-Wang, Kui; Stevenson, David E; Cooney, Janine M; Hellens, Roger P; Allan, Andrew C; Hoover, Emily E; Bradeen, James M
Background: Some apple (Malus × domestica Borkh.) varieties have attractive striping patterns, a quality attribute that is important for determining apple fruit market acceptance. Most apple cultivars (e.g. ‘Royal Gala’) produce fruit with a defined fruit pigment pattern, but in the case of ‘Honeycrisp’ apple, trees can produce fruits of two different kinds: striped and blushed. The causes of this phenomenon are unknown. Results: Here we show that striped areas of ‘Honeycrisp’ and ‘Royal Gala’ are due to sectorial increases in anthocyanin concentration. Transcript levels of the major biosynthetic genes and MYB10, a transcription factor that upregulates apple anthocyanin production, correlated with increased anthocyanin concentration in stripes. However, nucleotide changes in the promoter and coding sequence of MYB10 do not correlate with skin pattern in ‘Honeycrisp’ and other cultivars differing in peel pigmentation patterns. A survey of methylation levels throughout the coding region of MYB10 and a 2.5 Kb region 5’ of the ATG translation start site indicated that an area 900 bp long, starting 1400 bp upstream of the translation start site, is highly methylated. Cytosine methylation was present in all three contexts, with higher methylation levels observed for CHH and CHG (where H is A, C or T) than for CG. Comparisons of methylation levels of the MYB10 promoter in ‘Honeycrisp’ red and green stripes indicated that they correlate with peel phenotypes, with an enrichment of methylation observed in green stripes. Conclusions: Differences in anthocyanin levels between red and green stripes can be explained by differential transcript accumulation of MYB10. Different levels of MYB10 transcript in red versus green stripes are inversely associated with methylation levels in the promoter region. Although observed methylation differences are modest, trends are consistent across years and differences are statistically significant. Methylation may be associated with the presence of a TRIM retrotransposon within the promoter region, but the presence of the TRIM element alone cannot explain the phenotypic variability observed in ‘Honeycrisp’. We suggest that methylation in the MYB10 promoter is more variable in ‘Honeycrisp’ than in ‘Royal Gala’, leading to more variable color patterns in the peel of this cultivar.
Application of CRISPR-Cas12a temperature sensitivity for improved genome editing in rice, maize, and Arabidopsis
(Springer Nature, 2019-01-31) Malzahn, Aimee A.; Tang, Xu; Lee, Keunsub; Ren, Qiurong; Sretenovic, Simon; Zhang, Yingxiao; Chen, Hongqiao; Kang, Minjeong; Bao, Yu; Zheng, Xuelian; Deng, Kejun; Zhang, Tao; Salcedo, Valeria; Wang, Kan; Zhang, Yong; Qi, Yiping
CRISPR-Cas12a (formerly Cpf1) is an RNA-guided endonuclease with distinct features that have expanded genome editing capabilities. Cas12a-mediated genome editing is temperature sensitive in plants, but a lack of a comprehensive understanding on Cas12a temperature sensitivity in plant cells has hampered effective application of Cas12a nucleases in plant genome editing. We compared AsCas12a, FnCas12a, and LbCas12a for their editing efficiencies and non-homologous end joining (NHEJ) repair profiles at four different temperatures in rice. We found that AsCas12a is more sensitive to temperature and that it requires a temperature of over 28 °C for high activity. Each Cas12a nuclease exhibited distinct indel mutation profiles which were not affected by temperatures. For the first time, we successfully applied AsCas12a for generating rice mutants with high frequencies up to 93% among T0 lines. We next pursued editing in the dicot model plant Arabidopsis, for which Cas12a-based genome editing has not been previously demonstrated. While LbCas12a barely showed any editing activity at 22 °C, its editing activity was rescued by growing the transgenic plants at 29 °C. With an early high-temperature treatment regime, we successfully achieved germline editing at the two target genes, GL2 and TT4, in Arabidopsis transgenic lines. We then used high-temperature treatment to improve Cas12a-mediated genome editing in maize. By growing LbCas12a T0 maize lines at 28 °C, we obtained Cas12a-edited mutants at frequencies up to 100% in the T1 generation. Finally, we demonstrated DNA binding of Cas12a was not abolished at lower temperatures by using a dCas12a-SRDX-based transcriptional repression system in Arabidopsis. Our study demonstrates the use of high-temperature regimes to achieve high editing efficiencies with Cas12a systems in rice, Arabidopsis, and maize and sheds light on the mechanism of temperature sensitivity for Cas12a in plants.
Applying Green Complete Streets on Georgia Avenue NW: Redesigning an Urban Right-of-Way for Sustainable Mobility and Urban Water Quality
(2023) Mejias, Aliya; Ellis, Christopher D.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The public right-of-way (ROW) makes up nearly one-third of all the public space in cities. With the majority global population expected to reside in cities by 2050, climate change posing a significant threat to urban residents and infrastructure, impervious urban surface impacts on water quality, and knowing traffic fatalities in the US reached a 16-year high, cities must reconsider how this public good can serve people and the environment over to car-centric mobility. Using a segment of Georgia Avenue NW in Washington, DC, this thesis removes automobiles from the ROW to demonstrate how Green Complete Streets, which prioritizes sustainable transportation and urban water quality, can support urban livability on a corridor scale.
Applying Vegetation Dynamics Theory to the Long-Term Ecological Design and Management of Urban Public Parks: Upper Long Branch Stream Valley, Maryland
(2021) Podietz, Emma; Myers, David N; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Calls for ecological applications in landscape architecture have increased as the world faces compounding crises of climate change, biodiversity loss, and human disconnection with natural systems. Landscape architects are uniquely situated to address these crises as practitioners who engage at multiple scales with ecological systems, placemaking, and land use planning. A sustainability ethic exists within the discipline, but ecological principles and theory are inconsistently applied in built work. Vegetation dynamics theory generalizes the mechanisms of plant community change over time, and presents a useful framework for the planting design, long-term adaptive management, and stewardship of urban parks. The principles of the theory can be interwoven with ecological and aesthetic goals of designed landscapes. This thesis demonstrates how centering vegetation dynamics theory in urban park design can enhance ecological function of urban landscapes, create heightened place attachment through aesthetic and interpretive experience, and guide the long-term management and stewardship of urban ecosystems in the Mid-Atlantic United States.
Assessing evapotranspiration rates of a Mid-Atlantic red maple riparian wetland using sap flow sensors.
(2005-04-13) Renz, Jennifer Theresa; Momen, Bahram; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Riparian forests are unique due to increased exposure of trees to winds and radiation and the subsequent effects on the quality and quantity of water discharge from the system. Since "edge effects" can enhance evapotranspiration (ET) of exposed trees, ET rates of a first-order red maple riparian wetland were assessed with thermal dissipation probes during the 2002 growing season to address: a) if edge trees transpire more water daily than interior trees, b) correlations among sap flow rates and energy balance-derived estimates, c) variations in ecosystem ET estimates based on 6 scaling variables, and d) diurnal correlations between maximum sap flow rates and streamflow losses. Results from this study indicate that: a) edge trees transpire more water daily than interior trees during early summer, b) choice of scaling variable affects estimation of ecosystem ET rates, and c) maximum sap flow rates correlate with streamflow losses diurnally under specific environmental conditions.
Assessment of select isolates of Trichoderma virens as a potential biocontrol against Meloidogyne incognita
(2004-05-03) Mallozzi, Tonya Suzanne; Kratochvil, Robert J.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Three isolates of the soil-dwelling fungal organism, Trichoderma virens (Miller, Giddens and Foster) von Arx., were studied as potential biocontrols for the management of root-knot nematode (RKN) on bell pepper (Capsicum annuum L.). The study was conducted within the Moisture Replacement System (MRS), which was concurrently evaluated for its ability to serve as a culture system for Meloidogyne incognita (Kofoid and White) Chitwood and as an environment supportive of the growth and maintenance of Trichoderma isolates for biocontrol studies of this nature. Trichoderma isolates selected for study did not suppress populations of RKN on bell pepper under the conditions of this study. A review of the literature provided a multitude of complexities potentially contributing to the final results obtained. Investigation into these various complexities with the incorporation of the MRS will help to fully ascertain Trichoderma's potential as a biocontrol and perhaps reveal viable alternatives in the management of RKN.
Association Analysis in Soybean
(2008-08-29) Hwang, Eun-Young; COSTA, JOSE; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Association analysis is a new approach to identify the location of gene(s)/allele(s) of interest. There are a number of factors determining the feasibility of whole-genome association analysis which include the level of linkage disequilibrium (LD) and the magnitude of population structure in a population. The goal of this study was to evaluate the success of whole-genome association analysis in soybean germplasm accessions using DNA markers across the whole genome. Firstly, the extent of LD and the presence of population structure were estimated. Secondly, whole-genome association analysis was performed to detect the location of the allele/gene controlling flower color, pubescence color, and seed protein quantitative trait loci (QTLs) in 319 soybean [Glycine max (L.) Merr.] germplasm accessions. The soybean germplasm accessions had a relatively low level of LD which declined very rapidly to 0.8 in less than 4 Kbp as indicated by r² as well as highly diverse population structure. Despite the low LD and the presence of high population structure, whole-genome case-control analysis successfully detected the 65 bp insertion in the GmF3'5'H (GenBank acc. AY117551) gene controlling purple vs. white flower color, as well as a single base deletion in the F3'H (GenBank acc. AB191404) gene controlling tawny vs<\em>. gray pubescence color. However, there were 28 gray pubescence lines that did not contain the deletion suggesting that there is a second mutation determining the pubescence color alteration. In the case of seed protein QTL, whole-genome regression analysis detected one of four previously reported seed protein QTLs which reside on linkage group (LG) E and a new seed protein QTL on LG K. The detection of three other previously reported seed protein QTLs on LGs A1, I and M was not successful. It is unclear why association analysis was not successful in the detection of the three previously reported QTLs. However, a number of reasons including incomplete adjustment for population structure, lack of statistical power, an inadequate number of genetic markers in light of the low level of LD, and the power of association analysis to detect alleles with relatively modest genetic effects are suggested as possible reasons.
Auxin regulates adventitious root formation in tomato cuttings
(Springer Nature, 2019-10-21) Guan, Ling; Tayengwa, Reuben; Cheng, Zongming (Max); Peer, Wendy Ann; Murphy, Angus S.; Zhao, Mizhen
Adventitious root (AR) formation is a critical developmental process in cutting propagation for the horticultural industry. While auxin has been shown to regulate this process, the exact mechanism and details preceding AR formation remain unclear. Even though AR and lateral root (LR) formation share common developmental processes, there are exist some differences that need to be closely examined at the cytological level. Tomato stem cuttings, which readily form adventitious roots, represent the perfect system to study the influence of auxin on AR formation and to compare AR and LR organogenesis.
Bacterial communities of the specialty crop phyllosphere: response to biological soil amendment use, rainfall, and insect visitation
(2016) Allard, Sarah Michelle; Micallef, Shirley A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Microorganisms in the plant rhizosphere, the zone under the influence of roots, and phyllosphere, the aboveground plant habitat, exert a strong influence on plant growth, health, and protection. Tomatoes and cucumbers are important players in produce safety, and the microbial life on their surfaces may contribute to their fitness as hosts for foodborne pathogens such as Salmonella enterica and Listeria monocytogenes. External factors such as agricultural inputs and environmental conditions likely also play a major role. However, the relative contributions of the various factors at play concerning the plant surface microbiome remain obscure, although this knowledge could be applied to crop protection from plant and human pathogens. Recent advances in genomic technology have made investigations into the diversity and structure of microbial communities possible in many systems and at multiple scales. Using Illumina sequencing to profile particular regions of the 16S rRNA gene, this study investigates the influences of climate and crop management practices on the field-grown tomato and cucumber microbiome. The first research chapter (Chapter 3) involved application of 4 different soil amendments to a tomato field and profiling of harvest-time phyllosphere and rhizosphere microbial communities. Factors such as water activity, soil texture, and field location influenced microbial community structure more than soil amendment use, indicating that field conditions may exert more influence on the tomato microbiome than certain agricultural inputs. In Chapter 4, the impact of rain on tomato and cucumber-associated microbial community structures was evaluated. Shifts in bacterial community composition and structure were recorded immediately following rain events, an effect which was partially reversed after 4 days and was strongest on cucumber fruit surfaces. Chapter 5 focused on the contribution of insect visitors to the tomato microbiota, finding that insects introduced diverse bacterial taxa to the blossom and green tomato fruit microbiome. This study advances our understanding of the factors that influence the microbiomes of tomato and cucumber. Farms are complex environments, and untangling the interactions between farming practices, the environment, and microbial diversity will help us develop a comprehensive understanding of how microbial life, including foodborne pathogens, may be influenced by agricultural conditions.
Bacterial community diversity and variation in spray water sources and the tomato fruit surface
(2011-04-21) Telias, Adriana; White, James R; Pahl, Donna M; Ottesen, Andrea R; Walsh, Christopher S
Background: Tomato (Solanum lycopersicum) consumption has been one of the most common causes of produceassociated salmonellosis in the United States. Contamination may originate from animal waste, insects, soil or water. Current guidelines for fresh tomato production recommend the use of potable water for applications coming in direct contact with the fruit, but due to high demand, water from other sources is frequently used. We sought to describe the overall bacterial diversity on the surface of tomato fruit and the effect of two different water sources (ground and surface water) when used for direct crop applications by generating a 454- pyrosequencing 16S rRNA dataset of these different environments. This study represents the first in depth characterization of bacterial communities in the tomato fruit surface and the water sources commonly used in commercial vegetable production. Results: The two water sources tested had a significantly different bacterial composition. Proteobacteria was predominant in groundwater samples, whereas in the significantly more diverse surface water, abundant phyla also included Firmicutes, Actinobacteria and Verrucomicrobia. The fruit surface bacterial communities on tomatoes sprayed with both water sources could not be differentiated using various statistical methods. Both fruit surface environments had a high representation of Gammaproteobacteria, and within this class the genera Pantoea and Enterobacter were the most abundant. Conclusions: Despite the major differences observed in the bacterial composition of ground and surface water, the season long use of these very different water sources did not have a significant impact on the bacterial composition of the tomato fruit surface. This study has provided the first next-generation sequencing database describing the bacterial communities living in the fruit surface of a tomato crop under two different spray water regimes, and therefore represents an important step forward towards the development of science-based metrics for Good Agricultural Practices.
Benefits of gene flow are mediated by individual variability in self-compatibility in small isolated populations of an endemic plant species
(John Wiley & Sons Ltd., 2016-09-05) Frye, Christopher T.; Neel, Maile C.
Many rare and endemic species experience increased rates of self-fertilization and mating among close relatives as a consequence of existing in small populations within isolated habitat patches. Variability in self-compatibility among individuals within populations may reflect adaptation to local demography and genetic architecture, inbreeding, or drift. We use experimental hand-pollinations under natural field conditions to assess the effects of gene flow in 21 populations of the central Appalachian endemic Trifolium virginicum that varied in population size and degree of isolation. We quantified the effects of distance from pollen source on pollination success and fruit set. Rates of self-compatibility varied dramatically among maternal plants, ranging from 0% to 100%. This variation was unrelated to population size or degree of isolation. Nearly continuous variation in the success of selfing and near-cross-matings via hand pollination suggests that T. virginicum expresses pseudo-self- fertility, whereby plants carrying the same S-allele mate successfully by altering the self-incompatibility reaction. However, outcrossing among populations produced significantly higher fruit set than within populations, an indication of drift load. These results are consistent with strong selection acting to break down self-incompatibility in these small populations and/or early-acting inbreeding depression expressed upon selfing.