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Songul Severmutlu, Nedim Mutlu, Ercan Gurbuz, Osman Gulsen, Murat Hocagil, Osman Karaguzel, Tiffany Heng-Moss, Robert C. Shearman, and Rock E. Gaussoin

opportunity for water conservation when warm-season turfgrass species were used under Mediterranean-like climate in Australia, but data on drought resistance and water conservation are lacking for the Mediterranean region. Bermudagrass, buffalograss

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James E. Hook and Wayne W. Hanna

In our study, we sought to determine if an experimental cultivar of centipedegrass [`TC178'; Eremochloa ophiuroides (Munro) Hack.] had superior turf characteristics under extended droughts. Common centipedegrass (CC), vegetatively propagated `TC178' (VG178), and seed-propagated (F3) `TC178' (SD178) were evaluated in a 2-year controlled watering study that compared turf characteristics and drought resistance. The grasses were established under an automated rainfall shelter and were subjected to three drought regimes: watered twice per week (no stress), 2 to 3 weeks between watering (moderate), and 4 to 6 weeks between watering (severe). Turf characteristics (visual rating and clipping biomass) were measured weekly and soil water content profiles were measured daily. Visual ratings among cultivars were similar for no-stress conditions, but visual ratings of SD178 and VG178 were 18% higher than for CC for moderate stress and 28% higher for severe stress. At the end of moderate stress periods, clipping biomass of VG178 was 24% greater than for CC, but by the end of the severe stress periods, biomass from VG178 was 22% lower than for CC. Available soil water content profiles indicated that the three cultivars extracted soil water at the same rate. Visual ratings and growth decline with survival under severe stress showed that VG178 and SD178 had significantly better drought resistance than CC. `TC178' provides a superior appearance turf that will stand up to the droughts common in its adapted region.

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Mohamed A. Shahba, Mohamed S. Abbas, and Saad F. Alshammary

The demand for water has increased more than 300% during the past five decades ( Huffman, 2004 ). Therefore, the development of efficient irrigation management programs as well as the improvement of drought resistance of turfgrasses has become

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Fan Cao, Yunchu Wei, Xinwang Wang, Yongrong Li, and Fangren Peng

/dV), where V is the volume of free water, and P is pressure potential. The most bulk elastic modulus (ε max ), which represented the physical property of the cell wall, was also chosen and measured as one parameter for the evaluation of drought resistance

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J.D. Fry and W.S. Upham

The relative drought resistance of turf-type tall fescue (Festuca arundinacea Schreb.) cultivars compared to forage-type cultivars has not been well-documented. Greenhouse and field studies were conducted between 1991 and 1994 to determine rooting potential and drought response of a slow-growing, turf-type tall fescue (`MlC18'), a turf-type cultivar with a moderate growth rate (`Mustang'), and a forage-type cultivar (`Kentucky-31'). In the greenhouse, rooting was determined in sand or calcined clay using clear, polyethylene root tubes 4 cm in diameter by 122 cm deep. Root length density (RLD) was measured for 0- to 30-, 30- to 60-, 60- to 90-, and 90- to 120-cm depths. No differences were observed in RLD at the 0- to 30-cm depth. At other depths, RLD of `Mustang” was generally superior to that of `K-31' and `MlC18'. During a 3-week dry-down in the field in 1994, `MlC18' exhibited greater drought stress and a higher canopy minus air temperature than other cultivars. Advantages afforded by reduced mowing of slow-growing tall fescue cultivars may be negated by reduced drought resistance.

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Douglas S. Chapman and Robert M. Augé

Understanding physiological drought resistance mechanisms in ornamentals may help growers and landscapers minimize plant water stress after wholesale production. We characterized the drought resistance of four potted, native, ornamental perennials: purple coneflower [Echinacea purpurea (L.) Moench], orange coneflower [Rudbeckia fulgida var. Sullivantii (Beadle & Boynt.) Cronq.], beebalm (Monarda didyma L.), and swamp sunflower (Helianthus angustifolius L.). We measured a) stomatal conductance of leaves of drying plants, b) lethal water potential and relative water content, and c) leaf osmotic adjustment during the lethal drying period. Maintenance of stomatal opening as leaves dry, low lethal water status values, and ability to osmotically adjust indicate relative drought tolerance, with the reverse indicating drought avoidance. Echinacea purpurea had low leaf water potential (ψL) and relative water content (RWC) at stomatal closure and low lethal ψL and RWC, results indicating high dehydration tolerance, relative to the other three species. Rudbeckia fulgida var. Sullivantii had a similar low ψL at stomatal closure and low lethal ψL and displayed relatively large osmotic adjustment. Monarda didyma had the highest ψL and RWC at stomatal closure and an intermediate lethal ψL, yet displayed a relatively large osmotic adjustment. Helianthus angustifolius became desiccated more rapidly than the other species, despite having a high ψL at stomatal closure; it had a high lethal ψL and displayed very little osmotic adjustment, results indicating relatively low dehydration tolerance. Despite differences in stomatal sensitivity, dehydration tolerance, and osmotic adjustment, all four perennials fall predominantly in the drought-avoidance category, relative to the dehydration tolerance previously reported for a wide range of plant species.

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Yuguang Zhao, George C.J. Fernandez, Daniel C. Bowman, and Robert S. Nowak

Cumulative evapotranspiration (ETcum) patterns of 10 commercially available cool-season turfgrass species and cultivars were evaluated under progressive water stress in the semi-field conditions using a gravimetric mass balance method in three studies. At the end of water stress, the cultivars were visually scored for green appearance on a 0 (no green) to 10 (100% green) scale. A Gompertz nonlinear model gave a best fit to ETcum vs. days adjusted for pan evaporation variation. Two of the ETcum attributes (ti, the time during which the rate change in ET is zero, and ETmax, the maximum ET rate) estimated from the Gompertz model appeared to reflect efficient water-use attributes in the turfgrass. Among the physiological screening techniques studied, electrolyte leakage, relative water content, and the difference between canopy and air temperature appeared to separate cultivars by drought resistance and water use efficiency (WUE). These physiological attributes were also relatively easy to measure and had high correlations with color score and WUE. Biplot display is a graphical technique in which the interrelationships between the cultivars and water-use attributes can be displayed together. Based on ti, ETmax, color score, and physiological attributes, `Wabash' and `Bristol' Kentucky bluegrass (Poa pratensis L.), `Aurora' hard fescue (Festuca ovina var. duriuscula L. Koch.), and `FRT-30149' fine fescue (F. rubra L.) were identified as cultivars with higher WUE.

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Maria P. Fuentealba, Jing Zhang, Kevin E. Kenworthy, John E. Erickson, Jason Kruse, and Laurie E. Trenholm

drought-resistant genotypes. Huang (1999) suggested that the superior drought resistance in Prairie buffalograss compared with Meyer zoysiagrass was partly attributed to its greater RRDD. Turfgrass with a greater RRDD acquires access to deeper soil

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Jacob C. Domenghini, Dale J. Bremer, Jack D. Fry, and Gregory L. Davis

the field ( Hook et al., 1992 ; Karcher et al., 2008 ; Merewitz et al., 2010 ; Richardson et al., 2008 ; Steinke et al., 2010 ). Few studies, however, have assessed drought resistance of ornamental landscape species or directly compared drought

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James A. Zwack, William R. Graves, and Alden M. Townsend

Freeman maples (Acer × freemanii E. Murray) are marketed as stress-resistant alternatives to red maples (Acer rubrum L.), but few data from direct comparisons of these species are available. As a first step in comparing the stress resistance of red maple and Freeman maple, responses to drought were studied in Acer × freemanii `Autumn Fantasy', `Celebration', and `Marmo'. Plants grown from rooted cuttings were treated by withholding irrigation through four drought cycles of increasing severity that were separated by irrigation to container capacity. Drought reduced shoot dry mass, root dry mass, and height growth by 64%, 43%, and 79%, respectively, over all cultivars. Predawn leaf water potential was reduced by 1.16 MPa over all cultivars, and stomatal conductance data indicated water use was more conservative over all root-zone moisture contents after repeated cycles of drought. Specific mass of drought-stressed leaves increased by 25% for `Autumn Fantasy', and microscopy to determine leaf thickness and cellular anatomy is ongoing. `Autumn Fantasy' also had the lowest ratio of leaf surface area to xylem diameter, and `Autumn Fantasy' and `Celebration' had higher ratios of root to shoot mass than `Marmo'. Pressure-volume curve analysis revealed osmotic potential of drought-stressed plants at full turgor was 0.24 MPa more negative than controls, and droughted plants had a greater apoplastic water percentage than controls. Although osmotic adjustment during drought was similar among cultivars, differences in specific mass of leaves and in ratios of transpiring and conducting tissues suggest cultivars of Freeman maple vary in resistance to drought in the landscape.