Date of Award

8-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Advisor

Liu, Haibo

Committee Member

Park , Dara

Committee Member

Mount , Andrew

Abstract

Creeping bentgrass is the most popular turfgrass species on golf course putting greens throughout the world due to its fine texture, recuperative ability and dense growth habit. Drought stress is an environmental induced condition that is common to turfgrasses. Foliar fertilization is a common maintenance practice that is conducted and utilized on golf course putting greens due to the reduced total input, quick response and reduced environmental impact. The cuticle of creeping bentgrass creates a hydrophobic barrier that foliar applied fertilizers need to penetrate to be used by the plant. The cuticle morphology and composition is subject to change due to the environment. Therefore, the primary objectives of this thesis were to determine how the cuticle of creeping bentgrass was affected by drought stress, understand the influence of the cuticle on foliar fertilization absorption, and investigate methods to aid foliar applications.
Due to the limited literature on creeping bentgrass cuticle layer and methodology of studying the cuticle layer of grasses, a preliminary growth room study was conducted. Creeping bentgrass plugs were harvested and transplanted into a growth room where treatments were conducted. Treatments included a control with 100% ET returned and two drought treatments, where 50% and 25% ET was returned. Cuticle morphological and compositional changes were studied. Results revealed, 1–hexacosanol, comprising approximately 88% of the entire cuticle of creeping bentgrass. The remaining 12% was comprised of fatty acids, alkanes, an aldehyde and a five unknown compounds. Total wax load showed a pattern of increasing due to the drought stress. Cuticle crystalloid density increased significantly with drought stress. 15N–labeled urea was applied foliarly and % recovery was determined to evaluate the effect of drought on foliar uptake. Percent 15N recovery was significantly reduced in the two drought treatments compared to the control. The increase in total wax was negatively correlated with %15N recovery. Results suggest cuticle morphology and quantity may limit foliar fertilizer absorption.
A second study was conducted investigating drought stress on creeping bentgrass cuticle and foliar absorption. Treatments included control and drought where 100% or 50% ET was returned daily for 10d. Foliar absorption was studied with 15N–labeled urea applied with or without surfactant addition. Cuticle morphology and compositional changes were studied along with % 15N recovery. Total wax and crystalloid density increased significantly due to drought treatments. This was caused mainly by an increase in primary alcohols and fatty acids. Percent 15N recovery was affected by irrigation treatment and surfactant addition. The results presented suggest that the surfactant addition allows for improved penetration or adherence to cuticles influenced by drought stress.
Genetically modified plants can be engineered to tolerant environmental stresses, and could prove beneficial to regular maintenance practices. Transgenic creeping bentgrass was developed at Clemson University using the overexpression of Arabidopsis vacuolar H+–pyrophosphatase (AVP1) gene. Wild-type (WT) and transgenic (TG) cuticles were studied for differences in morphology and composition under control and drought treatments. The TG cuticle morphology was similar to the WT, but small differences were seen. Crystalloid density increased due to drought in the WT but not in the TG. Irrigation treatment had no significant effect on total cuticle wax for either WT or TG. Interestingly, the TG cuticle wax load was significantly higher (>1 μg cm–2) than the WT cuticle wax load. This was due to a larger amount of primary alcohols and fatty acids in the TG cuticle. Results suggest that the TG cuticle provides a less rough surface that would not influence a foliar applied solution, especially under drought stress where crystalloid density is not affected.
Fractal analysis was used to study and classify the crystalloid shape of WT and TG creeping bentgrass. The analysis was used to related cuticle chemical composition data, crystalloid shape and the fractal dimension. It was revealed that there was a significant difference in fractal dimension for the TG and WT crystalloids. The change in fractal dimension was thought to be the TG cuticle preparing itself for stress and therefore making its cuticle more hydrophobic to create a better protection barrier.

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