Browsing Plant Science & Landscape Architecture Theses and Dissertations by Subject "Agriculture, Plant Culture"
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- ItemBreeding Considerations for Improving Cadmium and Zinc Hyperaccumulation in Two Thlaspi caerulescens Populations(2004-05-05) Synkowski, Eva Claire Creighton; McIntosh, Marla S; Plant Science and Landscape Architecture (PSLA)Cadmium is the second most widespread soil metal contaminant in the world and it has been suggested that phytoremediation using hyperaccumulator plants could be used to effectively remove harmful levels of soil metals. This research was conducted to provide basic information necessary for developing a breeding program to improve the phytoremediation potential of Thlaspi caerulescens, a promising hyperaccumulator plant. By determining the genetic structure of the source populations and estimating the heritability of traits of interest, gain from selection was predicted. Bulk segregrant analysis of DNA polymorphisms was used to identify markers linked to cadmium hyperaccumulation. DNA markers would reduce time and expense of selecting superior genotypes. However, confounding effects from marker technology, experimental design, and sample size reduced the potential for implementing the detected markers in a breeding program. Future experiments may still detect markers for hyperaccumulation and the T. caerulescens populations studied are valuable for phytoremediation application.
- ItemCALIBRATING CAPACITANCE SENSORS TO ESTIMATE WATER CONTENT, MATRIC POTENTIAL, AND ELECTRICAL CONDUCTIVITY IN SOILLESS SUBSTRATES(2009) Arguedas Rodriguez, Felix Ruben; Lea-Cox, John D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The nursery and greenhouse industry requires precise methods to schedule irrigations, since current practices are subjective and contribute to water and nutrient runoff. Capacitance sensors were calibrated to precisely estimate substrate water content, matric potential, and pore water electrical conductivity (EC) in five soilless substrates. Regression coefficients (R2) ranged from 0.29 - 0.88 and 0.16 - 0.79 for water content in 5-cm and 20-cm column heights; matric potential R2 ranged from 0.10 - 0.98 and 0.79 - 0.98, respectively. Pore water EC calibrations were investigated, contrasting two sensor types and two prediction models. Results were applied to an empirical greenhouse dataset. Better precision and accuracy were achieved with ECH2O-TE sensor and Rhoades model. Capacitance sensors provide precise estimates of plant-available water in most soilless substrates, while pore water EC accuracy and precision depends on the sensor-model combination. These results will enable growers to precisely schedule irrigations based on water content and pore water EC.
- ItemThe Establishment and Persistence of American Ginseng (Panax quinquefolius L.) in Maryland Forests.(2005-05-26) Slak, David; McIntosh, Marla; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)American ginseng (Panax quinquefolius L.) is a profitable non-timber forest product with the potential of improving the sustainability of Maryland forests. In order to determine factors affecting Maryland ginseng production, ginseng seeds and roots were planted in forests in Eastern, Central, and Western Maryland in plots amended with no treatment, lime, or gypsum. The response variables measured included soil nutrients and ginseng persisence and establishment. In general, soil lime treatments improved establishment at the Eastern but not the Central or Western sites. The gypsum soil treatments did not significantly affect populations. Establishment of American ginseng grown from seed ranked by site was Western>Central>Eastern. Conversely, root establishment was best at the Eastern site. Across sites, soil pH, Ca, Mg, and K were positively correlated with establishment and persistence. Thus, American ginseng was grown throughout Maryland and ginseng production was enhanced by lime addition at the Eastern site.
- ItemFACTORS 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.
- ItemTRANSCRIPT PROFILING AS A METHOD TO STUDY FRUIT MATURATION, TREE-RIPENING, AND THE ROLE OF "TREE FACTOR" IN 'GALA' AND 'FUJI' APPLES(2005-04-20) Lin, Shu-fei; Walsh, Christopher S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)'Gala' and 'Fuji' are two high-quality apple (Malus domestica Borkh) cultivars. Their fruits mature and tree-ripen over a long period of time, and are resistant to pre-harvest drop. "Tree factor," a putative inhibitor of system 2 ethylene production is hypothesized to account for differences in ethylene production between attached and detached apple fruits. Three years of field data revealed two distinct patterns of maturation and ripening behavior in these two cultivars. 'Gala,' an early cultivar, demonstrated a typical positive "tree factor." Studies of the ripening pattern of 'Fuji' apple, which is a late-maturing cultivar, did not. 'Fuji' data were confounded by cold weather in the late fall. The natural progression of tree-ripening did not lead to the high concentrations of internal ethylene routinely measured in stored fruits. The stimulation of ethylene found in picked 'Gala' fruits ripened in the orchard might be explained by wounding stress coupled with a loss of nutrients and the water stress. Our alternative explanation for "tree factor" is the effect of continued termination of the phloem and xylem connection. The strength of the "tree factor" declined as 'Gala' fruit maturity progressed. Therefore, the "tree factor" tends to be more obvious in fruits with shorter growing period that mature during warm weather. To investigate differential gene expression that accompanies maturation and tree ripening, we used cDNA-AFLP (Amplified Fragment Length Polymorphism) to identify changes in transcript profiling during tree-ripening, and in the ripening of harvested fruits. Two hundred differentially-expressed transcript-derived fragments were isolated from 'Gala.' Ripening-related genes including those known to function in the key processes of defense and stress, cell wall degradation, pigment production and aroma biosynthesis were identified. Clones similar to housekeeping genes involved in protein biosynthesis and degradation, intracellular trafficking and sorting, cell structure and mobility, and metabolism-associated genes were also isolated. Expression patterns of these transcript-derived fragments were verified by using a different 'Gala' sample set on microarray and/or Northern blots. Our study supports the hypothesis that many ripening processes are under transcriptional control and that most of these differentially-expressed genes are highly conserved in fruits.
- ItemWATER 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.