Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item Forage Radish Cover Crop Effects on Mycorrhizal Colonization and Soil Test Phosphorus(2009) White, Charles Macaulay; Weil, Ray R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forage radish (Raphanus sativus L. var. longipinnatus) and cereal rye (Secale cereale L.) cover crops were examined for their effects on arbuscular mycorrhizal colonization and P acquisition of a subsequent corn (Zea mays L.) silage crop. Soil test P following these cover crops was also measured in bulk soil collected at three depths in the surface soil and in soil sampled within 3 cm of forage radish tap root holes. Forage radish never decreased mycorrhizal colonization and rye sometimes increased colonization of the subsequent crop compared to growing no cover crop. The extent of colonization of corn roots by arbuscular mycorrhizal fungi was positively correlated with corn shoot tissue P concentrations. Slight vertical soil test P stratification in the bulk soil occurred following both forage radish and rye cover crops at some sites. A large increase in soil test P occurred within 3 cm of forage radish tap root holes.Item Structure-function relationships of periplasmic membrane-derived oligosaccharides in salmonella growth and virulence(2006-11-09) Jun, Won; Theophanes, Solomos; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Membrane-derived oligosaccharides (MDO) consist of branched substituted β-linked sugar chains that are present in the periplasmic space of Escherichia coli and other gram-negative bacteria. Their common features are the presence of glucose as a major constituent sugar and their increased levels in low-osmolarity media. In several phytopathogenic bacteria, mutants defective in MDO synthesis failed to incite disease on the host plant. Very little is known about the role of MDO from Salmonella in virulence and osmotolerance. I have studied the structure-function relationship of MDO to understand if they play a role in Salmonella growth and virulence. MDO defective mutants of Salmonella Typhimurium were generated using a gene specific mutagenesis protocol and MDO were isolated and their glycosyl composition analyzed. The fractions containing the major peak from Sephadex G-10 gel filtration chromatography were pooled and subjected to DEAE-cellulose anion exchange chromatography to separate charged and neutral MDO. Compositional analysis revealed that MDO of wild-type consist of 94% glucosyl residues (hereafter referred to as glucose) in Salmonella Typhimurium FIRN while MDO of the delta mdoG mutant was comprised of only 24% glucose. Rhamnose, mannose, and galactose accounted for the rest. We also found that MDO composition varies in different chromosomal backgrounds. For example, glucose accounted for 41% of sugar residues in MDO of Salmonella Typhimurium SL1344. This proportion was further reduced to 24% in the delta mdoG mutant. Salmonella Typhimurium delta mdoG mutants (in FIRN as well as SL1344 chromosomal backgrounds) displayed reduced virulence in mice. Salmonella Typhimurium SL1344 delta mdoG mutant strain was recovered from the intestinal tissues and systemic tissues at a lower frequency than its parental wild-type strain and displayed a reduced ability of intracellular replication in macrophages. This defect in the delta mdoG mutant could be associated with the altered MDO composition. The delta mdoG mutant also invaded macrophages at a reduced efficiency and showed lower respiration rate under conditions mimicking acidic environments, such as stomach and phagosomes (pH 5.0). Correspondingly ATP level in the delta mdoG mutant was significantly reduced compared to the wild-type. These results support an important role for MDO in the virulence of S. Typhimurium. In competition assays using a mouse host, the delta mdoG mutant had a reduced capacity to colonize the mouse tissues. On the contrary, competitive assays on laboratory media showed that the mdoG mutation enhanced the growth of bacteria. A mixed pictured emerged when competition assays were performed by artificially inoculating fresh-cut produce. On tomato and cucumber, the wild-type cells emerged as dominant population after 3 days of growth, while no one strain dominated during the growth on honeydews, cantaloupes, watermelons, as well as acidic fruits such as apples. Together, these data demonstrate that specific wild-type MDO are required for efficient colonization and optimal virulence in mice. For environmental survival under different niches, no evidence was found for a specific need for MDO with particular sugar composition. Enteric pathogens with altered MDO (and reduced virulence) may serve as better "live vaccines".Item Sustainability of Cold-climate Strawberry Production Systems(2005-08-10) Stevens, Matthew Dexter; Lea-Cox, John D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Three cold-climate strawberry (Fragaria xananassa Duch.) production systems, conventional matted row (CMR), advanced matted row (AMR), and cold-climate plasticulture (CCP) were compared for aspects of sustainability including environmental impacts, economic viability and public acceptance over a three year production cycle. As a result of higher total yields, CMR had the highest overall revenue and estimated net profit of any system. The CCP had the lowest observed yield but the largest fruit in year one. Reduced fruit size and yield in the second harvest season indicate the CCP system may not be suitable for perennial production. Both the CCP and AMR production systems were better than CMR in preventing soil, nitrogen and pesticide loss due to rain-induced runoff, and had higher N uptake than CMR. The CCP and AMR systems were preferred over CMR in a pick-your-own consumer preference evaluation. AMR and CCP represent potential sustainable alternatives to the CMR system.Item GENETIC DIVERSITY AND LINKAGE DISEQUILIBRIUM IN WILD SOYBEAN, LANDRACES, ANCESTRAL, AND ELITE SOYBEAN POPULATIONS(2005-04-20) Hyten, Jr., David Lee; Costa, Jose M.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Domestication, founder effects, and artificial selection can impact populations by reducing genome diversity and increasing the extent of linkage disequilibrium (LD). To understand the impact of these genetic bottlenecks and selection on sequence diversity and LD within soybean [Glycine max (L.) Merr.], 111 genes and three chromosomal regions located on linkage groups A2, G, and J were characterized in soybean. Four soybean populations were evaluated: 1) the wild ancestor of soybean (G. soja), 2) the population resulting from domestication (landraces), 3) Asian introductions from which North American cultivars were developed (ancestors), and 4) elite cultivars from the 1980's (elite). A total of 438 single nucleotide polymorphisms (SNPs) and 58 insertions-deletions were discovered within the 102 genes. Sequence diversity was lower than expected in G. soja with an overall theta equal to 0.00235, and was less than half that value (theta = 0.00115) in the landraces. Domestication eliminated most unique haplotypes with G. soja containing 240 unique haplotypes while the landraces only contained 42 unique haplotypes. The founder effect of the introduction of soybean to North America followed by intensive artificial selection, resulted in only a 30% decrease in nucleotide diversity. A total of 738 SNPs were discovered and genotyped in the four populations throughout three chromosomal regions. In G. soja LD did not extend past 100 kb while in the three cultivated soybean populations LD extended from 90 kb up to 600+ kb, most likely as a result of increased inbreeding and domestication. The three chromosomal regions varied in the extent of LD within the populations. G. soja is the greatest resource for unique alleles and may be best suited for fine mapping utilizing association analysis. The landraces do not contain much more variability than the elite cultivars but may have enough diversity to facilitate genetic improvement of elite cultivars. Finally, due to the extended levels of LD in the landraces and the elite cultivars, whole genome association analysis may be possible for the discovery of QTL.Item FACTORS AFFECTING MEDIA pH AND NUTRIENT UPTAKE IN GERANIUMS(2004-08-30) Raymond, Carinne A.; MCINTOSH, MARLA S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Consumer demand has prompted an increase in geranium breeding efforts to produce new cultivars each season. It is hypothesized that the breeding for unique morphological traits has inadvertently resulted in changing the plant's ability to competitively take up nutrients. Under certain conditions, nutrient uptake of these novelty cultivars is less efficient, possibly caused by the influence of the geranium itself. Information collected from the container media is a good indicator of the container nutritional status and can be used as a diagnostic tool for early identification of nutritional problems and prevent plant loss. Severe nutrient deficiencies and toxicities have been associated with plants fertigated with low alkalinity water, suggesting that an unsteady pH in the rhizosphere coupled with low buffering capacity of irrigation water may cause preferential nutrient uptake. Maintaining a media pH that optimizes nutrient solubility while preventing interactions or precipitation is the goal for ensuring proper plant nutrition. Three experiments were performed to address the following objectives: 1.) Evaluate the effects of the geranium cultivar and class on the container media. 2.) Determine if media type affects nutrient availability and uptake by geraniums. 3.) Identify if preferential nutrient uptake occurs in response to changing pH and water alkalinity levels in the container media. Results indicate that a significant reduction in media pH occurs for zonal and ivy geraniums during a specific stage of growth and that the effects of pH and water alkalinity on nutrient uptake and are highly specific to the nutrient tested and the media type. Significant interactions between water alkalinity and pH contributed to preferential uptake of several of the tested nutrients especially at low water alkalinities. Overall, the differences in uptake were in most cases specific to cultivar, the stage of growth and nutrient tested and should be considered when determining optimal fertility requirements for specific geranium cultivars.Item CHARACTERIZATION OF THE MYO-INOSITOL (3) PHOSPHATE SYNTHASE GENE (MIPS) AND MAPPING OF A LPA MUTANT IN SOYBEAN (GLYCINE MAX (L.) MERRILL).(2004-08-25) Salmon, Katherine Diane; Kenworthy, William J.; Costa, Jose M.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Low phytic acid (LPA) is a mutation causing phosphorus to be stored as unbound phosphorus in the seed. LPA mutants show a high inorganic phosphorus (HIP) phenotype. Previous studies had indicated that LPA might be linked to the myo-inositol (3) phosphate synthase (MIPS) gene; this research attempted to associate a soybean HIP mutant with the MIPS gene. The parental and the F2 genotypes were tested in four ways: 1) SNP detection using the LCR protocol; 2) polymorphism detection with PCR; 3) high inorganic phosphorus (HIP) phenotype detection; and 4) oil and protein concentration. The two parental genotypes could not be differentiated in the LCR study. A PCR-based polymorphism was heritable in the F2 genotypes. HIP assay indicated multiple genes control the LPA mutant. A polymorphism was associated to the HIP phenotype. The three types of HIP phenotypes were not statistically different in oil and protein concentrations allowing implementation into a breeding program.Item WATER AND NUTRIENT DYNAMICS IN CONTAINER-NURSERY PRODUCTION SYSTEMS(2004-04-30) Ristvey, Andrew George; Lea-Cox, John D; Plant Science and Landscape Architecture (PSLA)Water quality remains a predominant issue within the Chesapeake Bay watershed, and nutrient loading continues to undermine the progressive recovery of this ecosystem. Until recently, the ornamental plant industry has had little information to develop better management practices to increase the efficiency of water and nutrient applications. This research used an integrated approach to examine container- production systems, to develop recommendations to increase nutrient uptake efficiency and reduce runoff. A 40-month field study examined the effects of various cultural practices on irrigation and nutrient uptake efficiencies. Under cyclic scheduling, drip irrigation applied 3 to 4.5 times less water than overhead irrigation and had significantly less runoff when plants were spaced at low densities. While drip irrigation is significantly more efficient, overhead irrigation is more practical and economically feasible for most small container-nursery stock. Time Domain Reflectometry (TDR) was examined as an alternative to cyclic scheduling and when used with overhead irrigation, water applications were half that of cyclic irrigation scheduling. . This research simultaneously documented nitrogen (N) and phosphorus (P) dynamics by examining nutrient applications, uptake and leaching over the forty months. In most cases, N and P uptake efficiency and runoff was negatively affected by overhead irrigation, particularly when soluble nutrients were applied via fertigation and at low plant densities. Nitrogen and P efficiencies ranged between 10 and 30% and were dependent upon methods of irrigation and fertilization, plant density and water use. The use of both drip and TDR-scheduled overhead irrigation reduced nutrient runoff to half that of the overhead irrigation program Intensive spring nutrient uptake studies showed that N influences the total growth of Rhododendron (azalea) and P uptake is a function of P fertilization rate and growth, influenced by N rate. Moderate N rates maintained optimal growth, while total P was only required at 1/20 of this N rate. Periodicity in nutrient uptake suggests seasonal timing of fertilizers may increase N and P uptake efficiency. Novel management strategies in the area of irrigation, fertilization, and cultural practices should be adopted by the ornamental industry to improve upon low efficiencies and reduce nutrient pollution in our watersheds.