Turf Performance Research Articles

Classification of Kentucky Bluegrass (Poa pratensis L.) Cultivars and Accessions Based on Microsatellite (Simple Sequence Repeat) Markers

Kentucky bluegrass (Poa pratensis L.) is an important facultative apomictic temperate perennial grass species used for both forage and cultivated turf. Through apomixis, this species is able to propagate diverse and odd ploidy levels, resulting in many genetically distinct phenotypes. A wide range of diverse cultivars and accessions of kentucky bluegrass have been previously characterized based on pedigree, common turf performance, and morphological characteristics to create a kentucky bluegrass cultivar classification system. The objectives of the current study were to assess the amount of genetic divergence among kentucky bluegrass cultivars, experimental selections, and plant collections and revise/update the original pedigree, turf performance, and morphological characteristics kentucky bluegrass classification system using recently described kentucky bluegrass microsatellite [simple sequence repeat (SSR)] markers. In this study, 247 kentucky bluegrass cultivars, experimental selections, and collections were genotyped using 25 SSR markers. SSR markers showed a strong correlation between genetic relatedness as assessed by molecular markers and the original kentucky bluegrass classification system and also provided justification for a revision/update of the classification system. Traditional classification types that were supported by the current SSR analysis include BVMG, Compact, Compact-America, Julia, Mid-Atlantic, Midnight, and Shamrock types. Newly proposed classification types included Cynthia, Jefferson/Washington, Limousine, P-105, Sydsport, and three Eurasian types. The majority of cultivars, experimental selections, and collections were uniquely identified with the current set of SSR markers. Genetic relationships of individuals as assessed by SSR markers closely matched known pedigrees. The current set of SSR markers can be used to rapidly genotype and assign new cultivars/accessions to kentucky bluegrass classification types and assess genetic relatedness among individuals and should be considered for use in a kentucky bluegrass plant variety protection program.

Effects of rootzone composition and irrigation regime on performance of velvet bentgrass putting greens. I. Turf quality, soil water repellency and nutrient leaching

The use of velvet bentgrass (Agrostis canina L.) on putting greens is limited by sparse knowledge on optimal maintenance. The objectives of this study were to determine the effects of rootzone composition (SS, straight sand; or GM, sand amended with 20% v/v garden compost) and irrigation regime (LF, light and frequent; or DI, deep and infrequent) on turfgrass visual quality, soil water repellency and nutrient leaching. The study was conducted from August 2007 to October 2009 on an experimental USGA green seeded in June 2007 with velvet bentgrass ‘Legendary’ at a coastal location in Norway (Landvik, 58° N). Better turf performance on GM than on SS was associated with less water repellency at most investigated depths in the 10-cm top layer, 88% lower nitrogen loss in the form of nitrate/nitrite during the first year after sowing, less injury caused by Microdochium nivale, and quicker recovery during both spring periods. A decrease in turf visual quality on SS receiving light and frequent irrigation in the second year was associated with strong water repellency in the mat layer. Compared with light and frequent irrigation, deep and infrequent irrigation resulted in better turf quality and lower drainage volumes.

Physiological Changes Associated with Wilt‐Induced Freezing Tolerance among Diverse Turf Performance Perennial Ryegrass Cultivars

ABSTRACTPerennial ryegrass (Lolium perenne L.) is a cool‐season turfgrass susceptible to low temperature injury. Wilt‐based irrigation (WI) is a common practice for scheduling irrigation to turf by allowing a mild, negative water imbalance to occur as an alternative to maintaining turf under nonlimiting soil moisture. Moisture stress has been shown to promote freezing tolerance but this has not been investigated in response to WI. Objectives of this study were to examine perennial ryegrass in response to WI (applied at 50% visual leaf roll) on freezing tolerance (median lethal temperature at 50% survival [LT50]), 13C discrimination (Δ), internal leaf‐to‐ambient CO2 concentration (ci:ca) ratio, leaf water, rooting, water use efficiency (WUE), and wilting tendency (days to wilt and number of wilt events) among three top‐performing (TP) and three bottom‐performing (BP) perennial ryegrass cultivars. Cultivars were selected based on turf quality trials from a northern location (Orono, ME). Plant measurements were made in the greenhouse in 2007 and 2008 comparing the first (single) and last (multiple) wilt cycle after 68 d of irrigation between well watered and WI. Multiple wilt exposures significantly enhanced freezing tolerance compared to a single wilt event for TP cultivars only, but gains in freezing tolerance were small (<1.0°C). Freezing tolerance (lower LT50 values) was generally associated with lower yield, WUE, and leaf water content. In some TP cultivars, wilt‐induced freezing tolerance was associated with greater wilting tendency and drought sensitivity indicated by lower Δ values and ci:ca ratio. Repeated wilt exposures increased rooting over a single wilt event.

Response of ‘Captiva’ St. Augustinegrass to Shade and Potassium

The effects of potassium (K) on stress tolerance of turfgrass have been documented for some environmental stresses but not for shade tolerance. ‘Captiva’ st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] was evaluated in this research project to determine the effects of K and shade on turf performance. The study was conducted at the University of Florida Envirotron Turfgrass Research Laboratory in Gainesville, FL. Grasses were planted in 15.2-cm plastic pots in a climate-controlled glass house. Two consecutive studies were conducted, the first from 20 May to 24 Oct. 2009 and the second from 18 Jan. to 20 June 2010. Grasses were placed in either full sun or under shade structures covered with woven black shadecloth to provide 30%, 50%, or 70% shade. Potassium was applied as potassium chloride (KCl) (0–0–62) at four rates (0, 0.6, 1.2, or 2.4 g·m−2) every 30 days. In both trials, turf visual quality and color scores and dry weight (DW) of shoot and root were lowest at 70% shade and highest at 30% shade. Turf visual quality score increased as K rate increased. Leaf length increased and leaf width decreased as shade level increased. Leaf tissue total Kjedahl nitrogen (TKN) and K concentration increased as shade level increased from 0% to 70%. Thatch DW was greatest at 70% shade and lowest at 30% shade. In the first trial, turf treated with a higher K rate had longer leaf length and greater root DW. Results from this study showed that ‘Captiva’ could maintain acceptable visual quality at up to 50% shade and that K at 2.4 g·m−2 may help turfgrass grow in a shaded environment by improving turf visual quality score, root growth, and leaf tissue K concentration. Additional field plot research should be conducted to verify these responses.

Occurrence of endophyte fungi on grasses in Poland – Review

Abstract The first reports from Pfannmoller et al. (1994) and Lewis (2000) regarding the level of Neotyphodium colonization of grasses in Poland identified ratios ranging from 20 % to 60 %. To date, the studies of endophytes in Poland have focused mainly on the rate of endophyte infection in subsequent years of plantation use, the effect of endophytes on turf performance and the occurrence of endophytes in cultivars of meadow fescue, tall fescue and perennial ryegrass. The aforementioned studies were mainly conducted on breeding varieties of grasses. From 2007 to 2009, intensive studies on Neotyphodium occurrence in ecotypes of wild grasses in Poland were conducted. The results suggest that Neotyphodium species are quite common in Poland and colonize roughly 70 % of semi-natural, used or abandoned grasslands. In this paper we review studies that have been conducted thus far in Poland regarding the occurrence of Neotyphodium spp. in grasses.

‘TifEagle’ Bermudagrass Response to Plant Growth Regulators and Mowing Height

Ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy] cultivars require considerable field research to determine best management practices for successful long‐term culture. A field study was conducted in 2004 and 2005 on an experimental ‘TifEagle’ bermudagrass putting green in Clemson, SC, to examine effects of plant growth regulators (PGRs) applied bimonthly and three mowing heights on turf performance. The PGRs included ethephon [(2‐chloroethyl)phosphonic acid] at 1.91 kg a.i. ha−1, flurprimidol [α‐(1‐methylethyl)‐α‐[4‐(trifluoro‐methoxy)phenyl]‐5‐pyrimidine‐methonol] at 0.07 kg a.i. ha−1, trinexapac‐ethyl [4‐(cyclopropyl‐α‐hydroxymethylene)‐3,5‐dioxo‐cyclohexane carboxylic acid ethyl ester] at 0.0175 kg a.i. ha−1, all pairwise PGR combinations at half the individual rates, and a nontreated control. Turf was mowed five times weekly at 2.50, 3.25, or 4.00 mm. Lateral regrowth with ethephon and trinexapac‐ethyl was comparable to nontreated turf, while flurprimidol impeded lateral regrowth ∼25%. All three PGRs reduced dry clipping weights, with flurprimidol most effective (>50% each harvest) and ethephon least effective (maximum 17%). Turf quality for trinexapac‐ethyl, ethephon, and flurprimidol was excellent (8.0–8.4), acceptable (6.8–7.1) and unacceptable (3.6–5.2), respectively. Compared to the control, root length density increased 33% with trinexapac‐ethyl, unaffected by ethephon, and reduced 25% with flurprimidol. Flurprimidol increased ball roll distances in morning (AM) and (PM) by 21 and 26 cm, respectively, trinexapac‐ethyl provided increases of 5 and 10 cm, respectively, while ethephon had no effect, compared to the control. No evidence of synergistic effects was observed for PGR combinations. Raising mowing heights increased lateral regrowth, turf quality, and root length density but decreased ball roll distances. Best overall performance of TifEagle bermudagrass was achieved with trinexapac‐ethyl, as it increased root length density, provided excellent turf quality, reduced vertical growth, did not impede lateral regrowth, and increased ball roll distances, compared to the control.

Low-input Performance of Zoysiagrass (Zoysia spp.) Cultivars Maintained under Dense Tree Shade

A 3-year study was conducted to evaluate the comparative performance of zoysiagrass (Zoysia spp.) cultivars for shaded environments in which inputs are minimized. Included in the study were commercial cultivars Diamond, Cavalier, Royal, Shadow Turf, Zorro, Zeon, Jamur, Crowne, Palisades, and Meyer. In July 2006, grass plugs were planted in a shade nursery comprised of live oak trees providing 89% shade. From 2007 to 2009, turf plots were periodically evaluated for quality, density, color, vertical canopy height, and extent of lateral spread. Overall turfgrass quality was noticeably reduced by the heavily shaded environment; however, some cultivars attained acceptable levels during midsummer periods. A turf performance index (TPI) was generated for ranking the cultivars that represented the number of times an entry occurred in the top statistical group across all parameters and rating dates. ‘Royal’, ‘Zorro’, and ‘Shadow Turf’ were the cultivars ranking in the top statistical grouping most often throughout the study. The results suggest that Z. matrellas may be better adapted than Z. japonicas for heavily shaded environments where inputs are conserved.

Irrigation Quantity Effects on Anthracnose Disease of Annual Bluegrass

ABSTRACTIrrigation can influence both turf vigor and playability of putting greens. Anthracnose (Colletotrichum cereale Manns sensu lato Crouch, Clarke, and Hillman) has become an increasingly destructive disease of annual bluegrass (ABG) [Poa annua L. f. reptans (Hausskn.) T. Koyama] putting greens, particularly when turf is under stress. This 3‐yr field study evaluated the effects of irrigation quantity (100, 80, 60, and 40% of reference evapotranspiration [ETo]) on anthracnose severity of ABG mowed daily to 3.2 mm. Severe drought stress (40% ETo) increased anthracnose severity in 2006, 2007, and 2008. Anthracnose was less severe under 60% ETo irrigation, and irrigating at 80% ETo reduced severity compared to 60% ETo Irrigating at 100% ETo initially reduced anthracnose severity compared to 40% ETo; however, 100% ETo resulted in similar disease severity later in the 2006 and 2008 seasons. While this response was not observed late in the 2007 season, plots maintained at 100% ETo had turf quality similar to plots irrigated at 40% ETo later in each year due in part to increased algal development. Irrigation to replace 80% ETo typically resulted in the least amount of disease and the best turf quality throughout the trial. Thus, irrigation to minimize drought stress while also avoiding continuous high soil water content is beneficial in reducing anthracnose and maintaining acceptable turf performance.

Isolation and Characterization of 88 Polymorphic Microsatellite Markers in Kentucky Bluegrass (Poa pratensis L.)

Kentucky bluegrass (Poa pratensis L.) is an important facultative apomictic temperate perennial grass species used for both forage and cultivated turf. Through apomixis, this species is able to propagate diverse and odd ploidy levels, resulting in many genetically distinct phenotypes. A wide range of diverse cultivars and accessions of kentucky bluegrass have been previously characterized based on common turf performance or morphological characteristics as well as by random amplified polymorphic DNA (RAPD) markers. Although previous characterization efforts have provided valuable information, the use of both morphological characteristics and RAPD markers for genetic diversity analysis has limitations. In the current report, we developed and characterized 88 novel microsatellite markers for kentucky bluegrass. Polymorphism for each marker was assessed in 265 kentucky bluegrass cultivars, experimental selections, collections, and hybrids. The number of alleles for individual microsatellites ranged from four to 81 with an average of 38.3 alleles per simple sequence repeat. These polymorphic microsatellite markers would be useful tools for investigating genetic diversity, creation of genetic linkage maps, assessment of levels of apomixis in cultivars and experimental varieties, and identification of aberrant progeny in apomictic kentucky bluegrass breeding programs.

Effects of SAG12-ipt and HSP18.2-ipt Expression on Cytokinin Production, Root Growth, and Leaf Senescence in Creeping Bentgrass Exposed to Drought Stress

Drought stress is a widespread abiotic stress that causes a decline in plant growth. Drought injury symptoms have been associated with an inhibition in cytokinin (CK) synthesis. The objectives of this study were to investigate whether expression of a gene (ipt) encoding the enzyme adenine isopentenyl phosphotransferase for CK synthesis ligated to a senescence-activated promoter (SAG12) or a heat shock promoter (HSP18.2) would improve drought tolerance in creeping bentgrass (Agrostis stolonifera) and to examine shoot and root growth responses to drought stress associated with changes in endogenous production of CK, and the proportional change in CK and abscisic acid (ABA) due to ipt transformation. Most SAG12-ipt and HSP18.2-ipt transgenic lines exhibited significantly higher turf quality, photochemical efficiency, chlorophyll content, leaf relative water content, and root:shoot ratio under drought stress than the null transformant or the wild-type ‘Penncross’ plants. Transgenic lines that had better growth and turf performance generally had higher CK content and a higher CK-to-ABA ratio, although the direct correlation of CK and ABA content with individual physiological parameters in individual lines was not clear. Our results demonstrated that expressing ipt resulted in the improvement of turf performance under drought stress in creeping bentgrass in some of the transgenic plants with SAG12-ipt or HSP18.2-ipt, which could be associated with the suppression of leaf senescence and promoting root growth relative to shoot growth due to the maintenance of higher CK level and a higher ratio of CK to ABA.

The Inheritance of Cold Tolerance and Turf Traits in a Seeded Bermudagrass Population

Low temperature tolerance is a principal factor limiting the use of seeded bermudagrass [Cynodon dactylon var. dactylon (L.) Pers.]. Therefore, increasing the winter tolerance of seeded bermudagrass cultivars has been a goal of turfgrass breeders for many years. Breeding methods for developing cultivars with increased tolerance to cold temperatures and superior turf characteristics could be improved by having accurate heritability estimates for cold tolerance and other turf performance traits. Parental clones and their respective polycross half‐sib families were established in a randomized complete block design with four replications in 2004 in Lexington, KY. Significant genetic variances were estimated for all traits except density, turf quality and color retention 2006. Narrow‐sense heritability estimates were found to range from 0 to 0.91 using the parent–offspring covariance method for estimating heritability. All heritabilities for spring green‐up were significantly (p < 0.01) different from 0. Positive predicted genetic gains were calculated for color, color retention, spring green‐up, and texture. These results indicate that genetic gains could be achieved if selections were made for these traits in this population.

Basic Marketing Strategies for Improving Business Performance in the Turf and Lawncare Industry

FE709, a 3-page fact sheet by John J. Haydu and Alan W. Hodges, discusses five simple marketing strategies that can improve the bottom-line performance of turf or lawncare businesses. Published by the UF Department of Food and Resource Economics, March 2008.

Evaluation of Drought Tolerance and Avoidance Traits for Six Creeping Bentgrass Cultivars

The objectives of this study were: 1) to compare drought responses between the more recently developed creeping bentgrass cultivars to standard cultivars and 2) to determine differential drought tolerance and avoidance characteristics associated with cultivar variation in drought resistance. Six cultivars of creeping bentgrass (Agrostis stoloniferia) (‘Penn A-4’, ‘Independence’, ‘Declaration’, ‘L-93’, ‘Penncross’, and ‘Putter’) were maintained in growth chambers at 20 °C day/15 °C night either well-watered or exposed to drought stress by withholding water for 17 days. Cultivars varied in turf performance and physiological responses (leaf relative water content and photochemical efficiency) to drought stress, which was reflected in their differences in drought tolerance (osmotic adjustment) and drought avoidance traits (water use rate and efficiency, root viability, root length, and number). ‘Penn A-4,’ ‘Independence,’ and ‘L-93’ generally performed better than other three cultivars under drought conditions, mainly through maintaining higher water use efficiency, root viability, root elongation, or root production. The majority of physiological parameters evaluated suggested that of the six creeping bentgrass cultivars examined in this study, the three cultivars with better ability to survive drought stress used mainly avoidance traits related to water use and water uptake.

Effects of Trinexapac‐Ethyl Foliar Application on Creeping Bentgrass Responses to Combined Drought and Heat Stress

Simultaneous drought and heat stress is detrimental to turfgrass growth. Growth regulators may influence plant responses to stresses. The objective of this study was to determine effects of pretreatment with trinexapac‐ethyl (TE) on creeping bentgrass (Agrostis stolonifera L.) responses to subsequent exposure to combined heat and drought stress. Plants were treated with TE (1.95 mL L−1 [v/v], Primo Maxx) every 14 d for 42 d and then exposed to combined drought and heat (35°C) in growth chambers. Application of TE increased turf quality and relative water content and chlorophyll content during 21 d of stress. Trinexapac‐ethyl–treated plants had increased growth rate and maintained constant canopy photosynthetic rate (Pn) and photochemical efficiency (Fv/Fm) during the stress period, while these parameters declined for the untreated control. Trinexapac‐ethyl–treated plants maintained lower evapotranspiration rate (ET) under nonstressed control conditions, but higher ET at 21 d of stress. Trinexapac‐ethyl–treated plants showed no differences from untreated plants in osmotic adjustment, and had lower levels of total nonstructural carbohydrates during the stress period. The study suggests that TE application enhanced turf performance under stress, as demonstrated by maintenance of higher turf quality and growth rate during a prolonged period of com bined stress. The beneficial effects of TE on bentgrass stress responses could be related to the maintenance of photosynthetic activities and greater level of cellular hydration. These and other published data indicate that use of TE on creeping bentgrass that seasonally experiences heat and drought stresses could benefit its performance.

Tufted Hairgrass Responses to Heat and Drought Stress

Tufted hairgrass [Deschampsia cespitosa (L.) Beauv.] is receiving increasing attention as a low-maintenance turfgrass for use in areas with reduced fertility or reduced sunlight. The objectives of this study were to examine physiological responses of tufted hairgrass to heat and drought stress and to distinguish whether better summer performance was related to better heat or drought tolerance. Four germplasm lines were chosen based on summer performance in field plots (two lines resistant to summer stress and two lines susceptible to summer stress) and were grown in growth chambers [14-hour photoperiod, 20/15 °C (day/night)]. Plants were exposed to either drought stress or heat stress (35/30 °C, day/night) for up to 49 days. Control plants maintained under normal conditions (20/15 °C, day/night, well watered) were included for both treatments. During the course of the study, single-leaf photosynthetic rate, photochemical efficiency, and relative water content were measured, and turf quality was visually rated. All parameters for all tufted hairgrass lines decreased under drought stress and heat stress, and the decline was more severe for summer stress-susceptible lines than for resistant lines. Lines that were previously considered resistant to summer stress exhibited superior photochemical efficiency under heat stress compared with the susceptible lines. When subjected to drought stress, the lines exhibited little or no differences in the measured parameters. These results suggest that observed variation in field summer performance among various tufted hairgrass germplasm lines may be mainly the result of their differences in heat tolerance. These results suggest that selecting for heat-tolerant germplasm could be important for further improvement in turf performance of tufted hairgrass during the summer.

Seasonal Changes in Root Metabolic Activity and Nitrogen Uptake for Two Cultivars of Creeping Bentgrass

Roots play important roles in plant responses to environmental changes. The objective of this study was to investigate seasonal changes and cultivar variation in root growth, respiratory activity, nitrogen uptake, and carbon allocation in relation to turf performance for two cultivars of creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.)] under field conditions. Two cultivars, `Penncross' and `L-93', were managed under USGA-specification putting green conditions, with daily irrigation and mowing at a 3-mm height from May to November in 1999 and 2000. Turf quality of both cultivars declined from the highest rating of 7 to 9 in May to 4 to 5 in August and September, and recovered to above 7 in October and November in both years. This corresponded to seasonal changes in root dry weight, dehydrogenase activity, nitrate reductase (NR) activity, carbon allocation to roots, and 15N uptake. Compared to Penncross, L-93 generally maintained better turf quality, as well as higher root dry weight, 15N uptake, NR activity, and carbon allocation during summer months. Previous studies often emphasize the important of a large, extensive root system. The results in the present study demonstrated that root metabolic activities followed the same seasonal pattern and cultivars variation as turf performance, and suggested that decline in root metabolic activities could be contributed to summer decline in turf quality for creeping bentgrass.

Minimum Water Requirements for Creeping, Colonial, and Velvet Bentgrasses under Fairway Conditions

Knowledge of water use requirements of various grass species is important for identifying grasses that persist with reduced water inputs and also for developing efficient irrigation management practices. This study was designed to examine minimum water requirements for maintaining acceptable quality fairways established to creeping (Agrostis stolonifera L.), colonial (A. capillaris L.) and velvet (A. canina L.) bentgrasses. Field experiments were conducted from July to November in 2002 and 2003. Plots were irrigated at four levels of irrigation on the basis of the percentage of actual evapotranspiration determined with minilysimeters (ETa): 100, 80, 60, and 40% ETa replacement. Turf performance was evaluated by measuring visual turf quality (TQ), canopy spectral parameters, canopy photosynthetic rates (Pn), and soil moisture status. Results generally demonstrated that irrigating at 100% ETa was not necessary to maintain acceptable TQ and physiological processes and that the minimum water requirements depended on species and time of year. Colonial bentgrass required irrigating at 80 to 100% ETa, while creeping and velvet bentgrasses required 60 to 80% ETa to maintain acceptable turf performance in the summer of 2002. During the summer treatment period in 2003, however, irrigating at 60% ETa was sufficient for all three species. Irrigating at 40% ETa in the fall treatment period in both 2002 and 2003 was sufficient to maintain acceptable TQ, canopy Pn, and comparable canopy growth parameters to plots receiving 100% ETa. The results from this study demonstrate the potential for significant water and monetary savings by utilizing deficit irrigation practices on bentgrass species used for golf course fairways.

Evaluation of Crested Wheatgrass Managed as Turfgrass

Typical turfgrass species often receive substantial inputs of water, fertilizer, chemicals, and cultural management, particularly in the Intermountain U.S. Plant materials that do not require these inputs and that also maintain acceptable levels of turf quality and performance are desirable in low-maintenance/limited irrigation situations. However, there is a lack of plant material that fits this description. Crested wheatgrass is a potential source of turf varieties for semi-arid regions and is the focus of current breeding efforts to improve its turf characteristics. This study examined implications of irrigation interval, mowing height, nitrogen fertilization, and cultivar selection on the performance of crested wheatgrass turf. While irrigation interval, mowing height, and cultivar affected performance, the application of nitrogen fertilization was the critical factor for maintaining the quality of crested wheatgrass turf under the conditions of this study. Regardless of the treatments imposed, crested wheatgrass turf performance declines during the hot summer months.

Changes in Protein Content, Protease Activity, and Amino Acid Content Associated with Heat Injury in Creeping Bentgrass

Various physiological processes may deteriorate in response to increasing temperatures, contributing to the decline in turf quality for cool-season turfgrasses during heat stress. This study was performed to investigate metabolic changes (membrane lipid peroxidation, total protein content, amino acid content, and protease activity) associated with turf quality decline for creeping bentgrass (Agrostis stolonifera Huds.) in response to gradually increasing temperatures for a short duration and prolonged exposure to lethally high temperature. Plants were subjected to increasing temperatures of 20, 25, 30, 35, and 40 °C for 7 days at each level of temperature [gradual heat stress (GHS)] or exposed to high temperature of 40 °C for 28 days [prolonged heat stress (PHS)] in growth chambers. During the GHS treatment, significant decline in turf quality occurred when plants were exposed to 30 °C for 7 days; simultaneously, malondialdehyde (MDA) content increased and total protein content in shoots decreased significantly compared to those at 20 °C. Protease activity increased at 25 °C and then decreased as temperature was elevated from 30 to 40 °C during the GHS treatment. Amino acid content decreased under GHS, beginning at 25 °C. Under the PHS treatment, turf quality declined and MDA content increased significantly, beginning at 14 days of PHS, while total protein content decreased at 7 days of PHS. Protease activity and amino acid content increased at 7 days of PHS, and then declined with longer stress duration. Our results indicated that protease activity, and amino acid and total protein content were more responsive to GHS or PHS than that of lipid peroxidation and turf quality. Changes in metabolic parameters of protease activity, amino acid and total protein content, and lipid peroxidation may contribute to leaf senescence and poor turf performance under severe or prolonged heat stress conditions for creeping bentgrass.

Creeping Bentgrass Establishment on Amended‐Sand Root Zones in Two Microenvironments

Sand‐based root zones are commonly used for construction of golf course putting greens. Objectives of this field study were to (i) evaluate sand‐based root zone mixtures varying in amendment (fine loam, peat, and inorganic) on the establishment of ‘L‐93’ creeping bentgrass (Agrostis stolonifera L.), (ii) compare findings to related published studies, and (iii) repeat the trial in two locations varying in air circulation to assess microenvironmental effect. Eleven root zone mixtures, using predominantly medium‐sized sand as the majority component, were replicated four times in a randomized complete block design nested within the two microenvironments. Plots were seeded in May 1998 and establishment was assessed to June 1999. Mixtures with a capillary porosity (−3 kPa water potential) at the high end of, or slightly exceeding, the United States Golf Association (USGA) criterion range (0.15–0.25 m3 m−3) provided more rapid establishment and better turf performance, yet root mass was lowest in these mixtures. Thus, variation in water availability among mixtures appeared sufficient to affect distribution of dry matter between roots and shoots. Mixtures amended to provide greater nutrient retention improved turf establishment; however, low water retention in the inorganic mixtures negated this advantage longer term as irrigation and fertilization shifted from establishment toward a maintenance objective. While shoot response to microenvironment was more limited, total root mass 1 yr after seeding was 24% greater in the open microenvironment than the enclosed, indicating that the initial effect of enclosed microenvironments on growth may go unrecognized during grow‐in unless rooting is assessed.