Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item MAKING APPLES BLUSH: UNDERSTANDING HOW THE COMBINED USE OF REFLECTIVE GROUNDCOVERS AND PLANT GROWTH REGULATORS IMPACT RED SKIN COLORATION AND QUALITY OF ‘HONEYCRISP’ APPLES IN THE MID-ATLANTIC US(2024) Miah, Md Shipon; Farcuh, Macarena; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Apples are among the most valuable fruits globally, with 'Honeycrisp' ranking as the top sales-producing cultivar in the US. However, challenges such as insufficient red skin coloration and increased preharvest fruit drop significantly diminish their market value. Reflective groundcovers have been reported to enhance apple skin coloration, while the application of the plant growth regulator AVG reduces fruit drop but may negatively impact skin coloration. Research on the impacts of these practices in mid-Atlantic US-grown apples remains limited. In this two years study, our aims were 1) to evaluate the effect of reflective groundcovers on solar radiation (PPFD, UV) distribution; 2) to assess the combined effect of reflective groundcovers and ethylene inhibitor (AVG) on preharvest fruit drop, ethylene production, red blush percentage, and overall fruit quality; 3) to investigate the combined effect of reflective groundcovers and ethylene inhibitor (AVG) on expression level of key anthocyanin and ethylene biosynthesis related genes; 4) to determine the combined effect of reflective groundcovers and ethylene inhibitors (AVG) in the accumulation of total anthocyanin. Apples underwent four treatment combinations of reflective groundcover (Extenday) and AVG (130 mg L−1). Our findings revealed that Extenday significantly enhanced skin coloration (>75% blush) through increased reflectance of PPFD and UV radiation, along with increased IEC, while also accelerating fruit maturity, i.e., overripening. In fact, Extenday-only treated fruit exhibited the highest upregulation of ethylene and anthocyanin biosynthetic-related genes, as well as total anthocyanins. Conversely, AVG notably reduced fruit drop and decreased IEC, delaying fruit maturity while significantly diminishing red coloration (30–48% blush). AVG treated fruit significantly suppressed the expression of key ethylene and anthocyanin biosynthetic structural and regulatory genes, as well as total anthocyanins. The combined application of Extenday and AVG synergistically decreased fruit drop while enhancing skin coloration (>50% blush), but without inducing overripening. This combination fine-tuned the transcript accumulation of ethylene and anthocyanin biosynthetic-related genes, as well as total anthocyanins, enabling 'Honeycrisp' fruit to exceed 50% blush, while moderately increasing IEC (compared to Extenday-only and control fruit), thus enhancing fruit economic value. Therefore, combining Extenday and AVG can boost the market value for 'Honeycrisp' apples in the mid-Atlantic US.Item THE USE OF ORGANIC WASTE PRODUCTS AS SOIL AMENDMENTS FOR TURFGRASS ESTABLISHMENT: EFFECTS AND REGULATORY INFLUENCES(2024) Morash, Jennifer Dawn; Lea-Cox, John; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of organic waste products as soil amendments in highly disturbed urban soil is poised to grow due to rising fertilizer costs, waste-management issues, and greater emphasis on creating sustainable circular economies. Despite the advantages of using waste products as organic amendments to enhance fertility, their incorrect use may result in short-term unintended consequences such as nutrient losses or the immobilization of plant-essential nutrients, which could diminish efforts to establish vegetation on disturbed soil. To avoid these consequences, transportation authorities – cited as the largest users of compost in some states – have implemented measures to improve product specifications. This research details the efforts of one such organization, the Maryland Department of Transportation State Highway Administration (MDOT SHA), and the results of an initiative to increase the quality of manufactured topsoil and compost use through agency topsoil specifications. After determining which products were most likely to be incorporated into manufactured topsoil (finely shredded wood mulch and composted leaf yard waste), two greenhouse microcosm experiments were conducted to evaluate plant growth responses and the efficiency of nutrient uptake compared to leachate losses when those amendments were used in accordance with MDOT SHA specifications. Composted yard waste provided excellent results while wood mulch suppressed growth in the short-term studies. A biosolids treatment was included in the experiments due to widespread availability and growing interest. Biosolids improved soil fertility and plant growth. However, the difference between nitrogen (N) uptake and leachate mass losses required a second set of experiments, to quantify the effects of four biosolids amendments on plant growth, nutrient uptake, and leachate losses. Treatments were applied at the rate recommended by UMD for turfgrass establishment (2.54 cm, incorporated) and included fresh biosolids, biosolids that were stockpiled for two years, two blended products made from either the fresh or aged biosolids and fine wood mulch, an inorganic fertilizer, and a control. Aging and wood fines reduced N leaching losses but at the expense of N inputs to soil. The cumulative N leachate mass loss from the new biosolids treatment was 63 times greater than the cumulative fertilizer total. Aging did not reduce phosphorus (P) leaching losses but wood fines did by diluting the concentration of P in blends. However, biosolids mostly retained P in the soil and cumulative fertilizer losses were 2 times higher. Overall, growth measurements showed that biosolids enhanced growth during the first and second growing seasons. However, based on the results of this research, 2.54 cm of pure biosolids is not required to enhance turfgrass establishment. An application of 1.27 cm of pure biosolids or 2.54 cm of a biosolid/wood fine blend should provide comparable enhanced turfgrass growth results while reducing overall nutrient leachate losses.Item IMPROVING IRRIGATION MANAGEMENT AND ROW COVER USE IN STRAWBERRY PRODUCTION IN THE MID-ATLANTIC REGION(2020) Belayneh, Bruk Eshetu; Lea-Cox, John D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Irrigation strategies that reduce water application and improve water use efficiency could be useful in strawberry production, to save water and reduce the environmental impact of nutrient leaching. Therefore, the effect of moisture availability on the physiology, growth, yield and fruit quality of strawberry (Fragaria X ananassa) was studied under field and greenhouse conditions by implementing deficit irrigation at decreasing matric potentials. Incremental drought stress significantly affected crop physiology, growth and yield, but not fruit quality. The results revealed both physiological and morphological adaptations of strawberries to incremental drought stress that are typical of isohydric plants. Since reduced irrigation applications led to proportional yield losses, there was no significant improvement in the irrigation water use efficiency/water productivity of the crop. Economic analysis showed that the loss of revenue as a result of reduced yields was of a much higher magnitude than the savings associated with reduced irrigation application, making adoption of reduced irrigation strategies such as deficit irrigation unlikely. Nevertheless, results revealed that soil moisture measurement-based irrigation management can be used to improve current (excess irrigation) grower practices, without impacting revenue. The effect of row covers on canopy and soil temperature, was studied in plasticulture strawberry production to more quantify their effects on crop phenology and frost mitigation. Row cover use increased the average temperature measured in the canopy and soil by 6.9 and 9.8%, respectively. Although this seems relatively insignificant, these temperature increases translated to an 84 and 122% increase in growing degree-day accumulation at the canopy and in the soil during a fall study period. In addition, increases in soil temperature were positively correlated with soil moisture. These results indicate the advantages that row covers can provide to growers, as a tool to enhance plant growth and for freeze and frost protection of plants. However, growers need to monitor environmental conditions at canopy level under row covers and in the ambient air in order to gain these benefits without negative consequences for yield.Item Local lettuce: heat tolerant romaine cultivars and vermicompost soil amendment to increase sustainability in the Mid-Atlantic(2014) Wallis, Anna Elizabeth; Walsh, Chris S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Local production of lettuce in the Mid-Atlantic utilizing heat-tolerant romaine cultivars and vermicompost soil amendment has the potential to significantly increase sustainability of agriculture. Heat tolerant cultivars would facilitate season extension into the summer. Vermicompost, compost produced using earthworms, may increase yield and quality of lettuce crops. This research tested a system incorporating these two practices. Success was assessed on lettuce yield and quality of lettuce across three seasons (spring, summer, and fall) and food safety risk of vermicompost. Several of the heat tolerant cultivars showed marketing potential when grown in the summer. Vermicompost did not significantly increase lettuce performance, but trends indicate that it may help, especially at higher rates. No food safety risk was associated with tested materials.