Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Plant and Environmental Science

Committee Chair/Advisor

Liu, Haibo

Committee Member

McCarty , Lambert B

Committee Member

Luo , Hong

Committee Member

Toler , Joe E


Bermudagrass (Cynodon ssp.) is the most popular warm-season turfgrass used in warm climatic regions of the world due its recuperative ability, high traffic tolerance, heat tolerance, and relative drought and salt tolerance. However, shade is a microenvironment in which bermudagrass performs poorly. Morphological limitations, such as reduced lateral stem growth and overall reduction of carbohydrate synthesis contribute to bermudagrass, a C4 plant, decline under shade. Therefore, primary objectives of this dissertation were to determine the genetic diversity of bermudagrasses grown in full-sunlight and shade, impacts of shade and cultural practices on bermudagrass spring transition, management recommendations to enhance bermudagrass putting greens under shade, and the impact of different types of light on warm-season turfgrasses. Secondary objectives of this dissertation determined winter shade and traffic impacts on creeping bentgrass putting greens
Due to the genetic variability and shade sensitivity of bermudagrasses, a two-year replicated field and greenhouse study determined the morphological and physiological characteristics and relative shade tolerance of 42 bermudagrass cultivars selected from the 2002 National Turfgrass Evaluation Program (NTEP). In the field study, few trends emerged where one cultivar could be recommended above all others. Also, experimental cultivars performed well compared to industry standards throughout the year. For example, 'OKC 70-18' and 'SWI-1046' (spring), 'TiftNo.2' (summer), and 'SWI-1003', 'SWI-1044', 'SWI-1045', 'SWI-1001', 'TiftNo.4', 'Tifway', and 'TiftNo.2' (fall), were in the top statistical category for turfgrass quality (TQ), shoot chlorophyll, clipping yield, root biomass, and thatch. In the greenhouse study, cultivars with best shade tolerance were 'Celebration', TiftNo.4, 'TiftNo.1', and 'Transcontinental'. Cultivars with intermediate shade tolerance included 'Aussie Green', 'MS-Choice', 'Princess 77', 'SWI-1045', 'SWI-1041', and 'SWI-1012'. Most shade sensitive cultivars included 'SWI-1014', 'Arizona Common', 'Sundevil', 'SR 9554', 'GN-1', and 'Patriot'. Greenhouse results indicate genetic variability of shade tolerance exists among bermudagrasses, while future bermudagrass improvement focusing on shade tolerance is promising
Two lysimeter studies were conducted from March to July 2006 and 2007 to evaluate fairway-type bermudagrass cultivars spring green-up (SGU) when shade is a growth limiting factor and to evaluate the impacts of different cultural practices (overseed, colorant use, and dormant turfgrass) and shade on 'TifEagle' bermudagrass (Cynodon dactylon (L.) Pers. X C. transvaalensis Burtt-Davy) spring transition and summer performance. Fairway-type cultivars, Celebration and TiftNo.4, did not show significant SGU delays due to shade in year II. However, Yukon and Riviera delayed SGU 11% and 50% compared to full-sunlight treatments on 9 May 2007. Compared to full-sunlight, TiftNo.4 and Celebration SGU and summer TQ was least affected by shade. Although cultivar summer TQ differences were noted when grown under shade, all cultivars TQ was below the acceptable threshold of 7 by 31 July. In another lysimeter study, shade negatively impacted TifEagle bermudagrass SGU for all treatments on various rating dates. By the end of May, overseed sun treatment had 39% greater SGU compared to overseed shade treatment. Shade-grown colorant-treated TifEagle showed ~37% SGU reduction from week 2 through week 5 ratings compared to sun-grown colorant treatment. On the final SGU rating date, sun-grown colorant treatment enhanced SGU 39% compared to sun-grown overseed treatment. This study indicates colorant-use may provide an alternative to overseeding for bermudagrass by providing adequate winter color at certain sites and a stronger bermudagrass base compared to overseeding
A two-year field study from 15 June to 15 September 2006 and 2007 at Clemson University determined the best combination of management practices for sustaining a high quality 'Champion' bermudagrass putting green under shade. Treatments included 55% full-day shade, trinexapac-ethyl (TE) applications (0.05 kg a.i. ha-1 2wk-1), iron (Fe) applications (2.7 kg a.i. ha-1 2wk-1), and nitrogen (N) applications as urea (46-0-0) at rates of 147, 293, and 437 kg ha-1 yr-1. Overall, Fe applications had minimal impacts on parameters measured. Increasing N rates linearly increased TQ when grown under full-sunlight. However, increasing N rates linearly decreased TQ scores under 55% full-day shade. Applying TE resulted in a linear TQ increase for full-sunlight and shade-grown Champion bermudagrass. A 15% chlorophyll concentration increase was noted for TE-treated plots compared to non TE-treated plots when grown under shade. Applying N at 293 kg ha-1 yr-1 increased thatch thickness 26% compared to the 147 kg ha-1 yr-1 N rate. Champion bermudagrass did not provide an acceptable quality putting green when grown under 55% full-day shade, however, adjusting chemical and cultural management practices improved Champion bermudagrass putting green when grown under shade
In 2007, two repeated greenhouse research projects were initiated to investigate the physiological and morphological responses of 'Diamond' zoysiagrass (Zoysia matrella (L.) Merr), 'Sea Isle 2000' (Paspalum vaginatum Sw.) seashore paspalum, Tifway bermudagrass, and Celebration bermudagrass to various light spectral qualities. Light treatments included a full-sunlight control and four different color shade cloths filtering wavelengths 560 - 720 nm (blue shade cloth), 360 - 520 nm (yellow shade cloth), 360 - 560 nm (red shade cloth) and 360-720nm (black shade cloth). Red to far red ratio for each cloth was ~1.171, while percent light reduction for each cloth was ~65%. Data collection included visual TQ, clipping yield, total shoot chlorophyll, leaf width, total root biomass, root length density (RLD), specific root length (SRL), and root and shoot total non-structural carbohydrates (TNC). Overall, black shade most negatively inhibited parameters measured followed by blue shade, while yellow and red shade performed similarly. For turfgrasses, Diamond was the most shade-tolerant, while Tifway was the most shade-sensitive. Celebration and Sea Isle 2000 performed similarly. This study implies different types of shade significantly impact the performance of warm-season turfgrasses
Two replicated field studies were conducted to evaluate winter shade tolerance under various reduced light environments and winter traffic tolerance of 'L93' creeping bentgrass (Agrostis stolonifera var. palustris (Huds.)). In the first field study, objectives were to evaluate winter shade tolerance of 'L93' creeping bentgrass under various reduced light environments (55% and 95%), including effects of morning vs. afternoon shade, effect of trinexapac-ethyl (TE) (4-(cyclopropyl--hydroxy-methylene)-3,5-dioxy-cyclohexanecarboxylic acid ethyl ester) application on shade tolerance, and summer month performance following a winter shade environment. Under shade stress, consistent TE applications every two weeks during winter negatively impacted bentgrass growth and color, however, TE enhanced spring recovery from 95% winter shade damage. Morning or afternoon shade minimally impacted parameters measured. Overall, moderate to heavy winter shade may not limit creeping bentgrass performance as a putting green in the transition zone. In a separate field study, treatments consisted of no traffic (control), foot traffic, and walk behind mower traffic (rolling) at 0700 and 0900 when canopy temperatures were at or below 0oC. Under traffic stress, on all TQ rating dates, 0700 rolling traffic decreased TQ by ~1.1 units compared to foot traffic at 0700. In December, regardless of traffic application time, rolling traffic reduced bentgrass shoot growth ~17%. By the end of March, all treatments had acceptable TQ. Root TNC and shoot chlorophyll concentrations were unaffected in May and August. This study indicates bentgrass damage due to winter traffic is limited to winter and early spring months and full recovery should be expected by summer



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