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theses

Considered a “stress nutrient”, silicon has been reported to provide beneficial effects to plants grown under biotic and abiotic stresses. The mechanisms considered are either an accumulation of absorbed silicon in the epidermal tissue, or an expression of metabolic or pathogenesis-mediated host defense responses. In the case of silicon nutrition, plants are considered silicon accumulators or non-accumulators. It is commonly accepted that accumulators can benefit from silicon, but studies have shown that non-accumulators can sometimes benefit from silicon nutrition when under stress on a case-by-case basis. The objective of this dissertation study was to reveal the potential beneficial effects of silicon nutrition on three hydroponically grown silicon non-accumulator vegetable species, lettuce, bok choy, and basil, representing the common leafy green families of Asteraceae, Brassicaceae, and Lamiaceae. None, low and high levels of silicon (0, 25 and 75 ppm) were added to the hydroponic nutrient solution. The plants were grown under temperature stresses (heat stress to lettuce and bok choy, and cold stress to basil), cut-and-grow-back stresses (lettuce, bok choy and basil), and biotic stresses (lettuce powdery mildew, simulated insect chewing on bok choy, and basil downy mildew). Plant growth, stress responses, and tissue nutrient analysis (including silicon) were evaluated. When grown under heat stress, silicon treatments failed to provide any beneficial effects for lettuce and bok choy. Basil grown under cold stress benefited from silicon treatments resulting in increased cold hardiness and improved survival rates after rates after a single frost event. Lettuce, bok choy, and basil grown under temperature stresses absorbed silicon in small quantities. The cut and grow back treatment did not result in silicon accumulation in lettuce, bok choy, and basil. The lettuce powdery mildew experiments failed due to the inability to establish sufficient disease pressure. The mechanical wounding treatment (representing insect chewing damage) in bok choy did not result in enhanced Si accumulation. For basil exposed to downy mildew, silicon treatments marginally increased the disease resistance without enhancing silicon accumulation. For most of the experiments, Si nutrition did not alter the content of other macro- and micro nutrients in both shoots and roots of lettuce, bok choy and basil. Future experiments are needed to evaluate the feasibility of using silicon as an effective BDM control agent for commercial growers. This dissertation research provided valuable information for understanding the physiology of silicon in non-accumulator plant species, and its potential beneficial effects for non-accumulator crops.

ETD_10518

Ph.D.

Includes bibliographical references

doi:10.7282/t3-k79b-j942

ETD doctoral

The author owns the copyright to this work.