Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item INVESTIGATING CRUMB RUBBER AMENDMENTS FOR EXTENSIVE GREEN ROOF SUBSTRATES(2010) Solano Torres, Sonia Lorelly; Lea-Cox, John D; Ristvey, Andrew G; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Extensive green roof systems can mitigate urban stormwater by capturing rainfall and reducing runoff volume. Green roof substrates, often made from expanded shales, slates and clays are fundamental for roof hydraulic dynamics, and for providing optimal plant growth conditions. However, these substrates occasionally impose load limitations for retrofitting existing infrastructure. This research studied recycled-tire crumb rubber, as a light-weight material for amending green roof substrates. Zinc release from crumb rubber was quantified, and the interactions with commercial rooflite® substrate and the effect of high Zn concentrations on the growth and uptake by Sedum were studied. Zn was found to leach from crumb rubber in quantities that could negatively affect plant growth; however, Zn was adsorbed onto cation exchange sites of the mineral and/or organic portion of rooflite®, preventing negative growth effects in Sedum. Crumb rubber could be utilized as an amendment with substrates having high cation exchange capacities.Item CALIBRATING 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.Item IN VITRO INDUCTION OF POLYPLOIDY IN CERCIS YUNNANENSIS HU ET CHENG(2009) Nadler, Joshua Daniel; Coleman, Gary D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Methods for in vitro induction of polyploid Cercis yunnanensis Hu et Cheng using oryzalin were developed and evaluated. Methods included treating either shoot or callus tissue for different exposure durations with either an aqueous solution of 150 micromolar oryzalin or the addition of oryzalin directly to solid media. Polyploid nuclei were determined by flow cytometry for all oryzalin treatments. Although the results indicate that most tissues measured were likely chimeras with respect to DNA content. Results indicate that treating shoot tissue with an aqueous solution of oryzalin for 12 to 96 hours produced tetraploid plants irrespective of the type of shoot explant treated. An unstable octaploid was formed from the treatment of a pre-cultured lateral shoot in an aqueous solution of oryzalin for 96 hours. In contrast shoots cultured on the solidified media failed to produce polyploid plants and there were no statistical differences between callus treatments regarding polyploid induction.Item Factors Affecting Fungicide Performance when Targeting Dollar Spot Disease in Creeping Bentgrass(2009) Pigati, Ray L.; Dernoeden, Peter H; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Creeping bentgrass (Agrostis stolonifera) is commonly grown on golf course fairways and dollar spot (Sclerotinia homoeocarpa) is perhaps the most chronically severe disease of bentgrass. Field studies were conducted to: a) determine the influence of simulated rainfall and two mowing timings (AM and PM) on the performance of four fungicides, and b) to assess the effects of two fungicide spray volumes (468 and 935 L water ha-1) and application timings (AM and PM) on dollar spot control in creeping bentgrass. Fungicide effectiveness generally was reduced by simulated rain imposed about 30 minutes after application. Boscalid and chlorothalonil were most and least rain-safe; respectively, and propiconazole and iprodione were intermediate in rain-safeness. Fungicide performance was improved by mowing in the AM prior to fungicide application. A tank-mix of chlorothalonil + propiconazole was unaffected by spray volume or application timing, but the performance of chlorothalonil and propiconazole applied separately was inconclusive.Item Microbial Ecology and Horticultural Sustainability of Organically and Conventionally Managed Apples(2008) Ottesen, Andrea; Walsh, Christopher S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Objectives: Organically and conventionally managed apple trees (Malus domestica Borkh) were evaluated for three growing seasons (2005-2007) to examine the impact of organic and conventional pesticide applications on the microbial ecology of phyllosphere and soil microflora. An important objective was to establish if organic or conventional selection pressures contribute to an increased presence of enteric pathogens in phyllosphere microflora. The horticultural and economic sustainability of the organic crop was also compared to the conventional crop with regard to fruit yield and input costs. Methods: Microbial populations from phyllosphere and soil environments of apple trees were evaluated using clone libraries of 16S rRNA gene fragments. Clones were sequenced and software was used to assess diversity indices, identify shared similarities and compute statistical differences between communities. These measurements were subsequently used to examine treatment effects on the microbial libraries. Phyllosphere Results: Eight bacterial phyla and 14 classes were found in this environment. A statistically significant difference between organically and conventionally managed phyllosphere bacterial microbial communities was observed at four of six sampling time points. Unique phylotypes were found associated with each management treatment but no increased human health risk could be associated with either treatment with regard to enteric pathogens. Soil Results: Seventeen bacterial phyla spanning twenty-two classes, and two archaeal phyla spanning eight classes, were seen in the 16S rRNA gene libraries of organic and conventional soil samples. The organic and conventional soil libraries were statistically different from each other although the sampling depth was not sufficient to make definitive inference about this environment. Horticultural Results: Fruit yields from organically managed apple trees were from one half to one third of the yields from conventionally managed trees. Based on input costs, organic fruit was about twice as expensive to produce. Asian pears (Prunus serotina) were also included in this horticultural analysis and showed greater field tolerance as an organic specialty niche crop than apples.Item Characterization of PtFD1, a bZIP transcription factor using transgenic poplars(2006-11-02) Wu, Minggang; Coleman, Gary; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dormancy is an adaptive mechanism that enables plants to survive unfavorable environmental conditions and resume growth when the conditions become favorable again. Bud formation is the morphological event associated with bud dormancy. The research presented in this thesis focuses on the role of PtFD1, a bZIP transcription factor, in apical bud development in poplar. This research included the construction of binary Agrobacterium vectors for the overexpressing of PtFD1 and for down regulation or silencing of PtFD1 expression using RNAi technology. These vectors were used to create transgenic poplars (Populus alba×Populus tremula) with altered expression of PtFD1. The overexpression of PtFD1 prevented apical bud development while apical bud development appeared normal in PtFD1 RNAi expressing plants. Flowering was also induced in long days in poplars overexpressing PtFD1. Anatomical studies indicate that overexpression of PtFD1 impinges on bud scale development during short day induced bud formation.