Search Results

Ultraviolet-B (280–320 nm) radiation is one of the major factors causing quality decline of transplanted turfgrass sod. Information on physiological parameters for assessing turfgrass tolerance to ultraviolet-B stress is lacking. The objective of this study was to evaluate ultraviolet-B tolerance of four cool-season turfgrass species and varieties using selected physiological parameters under artificial ultraviolet-B radiation stress. The physiological performance of 18 varieties of tall fescue (TF; Festuca arundinacea Schreb.), chewings fescue (CF; Festuca rubra L. ssp. commutata Gaud.), perennial ryegrass (PRG; Lolium perenne L.), and kentucky bluegrass (KBG; Poa pratensis L.) were subjected to continuous, artificial ultraviolet-B radiation (70 μmol·m⁻²·s⁻¹) for 10 days. Visual quality ratings of TF, CF, PRG, and KBG measured at Day 10 were reduced by 49%, 18%, 51%, and 74%, respectively, relative to that at trial initiation. Ultraviolet-B tolerance in CF was the greatest, KBG was the least, and TF and PRG were intermediate. ‘Ebony’ was the most ultraviolet-B-tolerant TF variety, whereas ‘BlueTastic’, ‘BlueRiffic’, and ‘747’ had greater ultraviolet-B tolerance than the other four KBG varieties. No differences were observed in ultraviolet-B tolerance between varieties in either CF or PRG. The ultraviolet-B-tolerant species had less electrolyte leakage (EL), greater canopy photochemical efficiency (PEc), and relatively smaller and slower upregulation in antioxidant superoxide dismutase (SOD) activity relative to ultraviolet-B-sensitive ones. The results suggest that EL, PEc, and SOD may be used as physiological parameters in selecting ultraviolet-B-tolerant species and varieties for sod production and lawn establishment.

Superoxide dismutase (SOD) activity is closely associated with stress tolerance of creeping bentgrass [Agrostis stoloniferous L. var. palustris (Huds.) Farw (syn. A. palustris Huds.)]. This study was conducted to investigate the influence of two plant growth regulators (PGRs) on the endogenous antioxidant SOD level and photochemical activity in `Penncross' creeping bentgrass grown under two fertilizer regimes. Mature `Penncross' was treated monthly with TE at 0.44 g a.i./100 m² and PPC at 3.37 g a.i./100 m² from May through November at the Virginia Tech Turfgrass Research Center, Blacksburg, Va. Foliar application of TE and PPC increased SOD activity, photochemical activity, and Fm730/Fm690 ratio of creeping bentgrass under the two fertilization regimes as well as when the grass was exposed to a low soil moisture environment. TE reduced clipping weight consistently regardless of the fertilization regime. In contrast, PPC increased clipping weight slightly. Both TE and PPC significantly reduced Dollar spot disease (Sclerotinia homoeocarpa Bennett) under both high and low fertilization regimes. No significant fertilization × PGR interactions for SOD, photochemical activity of PS II, and Fm730/Fm690 were observed in well-watered or drought stressed bentgrass. Improvement in stress tolerance of creeping bentgrass by the PGRs appears to be associated partially with an increase of endogenous SOD activity. Chemical names used: trinexapac-ethyl (TE); propiconazole (PPC).

Drought stress is one of the major limiting factors for plant growth and development. The mechanism of drought tolerance has not been well understood. This study was designed to investigate proline and antioxidant metabolism associated with drought tolerance in transgenic tobacco (Nicotiana tabacum) plants overexpressing the OjERF gene relative to wild-type (WT) plants. The OjERF gene was isolated from mondo grass (Ophiopogon japonicus). The OjERF gene, driven by the CaMV35S promoter, was introduced into tobacco through agrobacterium (Agrobacterium tumefaciens)-mediated transformation. Five transgenic lines were regenerated, of which transgenic Line 5 (GT5) and Line 6 (GT6) were used to examine drought tolerance in comparison with WT plants in a growth chamber. Drought stress caused an increase in leaf malondialdehyde (MDA) and electrolyte leakage (EL), proline content, superoxide dismutase (SOD), and catalase (CAT) activity in both transgenic lines and WT plants. However, the transgenic lines had lower MDA content and EL and higher proline content, SOD and CAT activity relative to WT under drought stress. The activities of SOD and CAT were also greater in the transgenic lines relative to WT plants under well-watered conditions (Day 0). The OjERF activated the expression of stress-relative genes, including NtERD10B, NtERD10C, NtERF5, NtSOD, and NtCAT1 in tobacco plants. The results of this study suggest that the OjERF gene may confer drought stress tolerance through upregulating proline and antioxidant metabolism.

Recent advances in bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon] breeding and cultural management practices have enabled its use as a sports surface in U.S. Department of Agriculture cold hardiness zones 5 and 6. Use of these more cold-hardy bermudagrass cultivars further into transition- and cool-season zones increases the probability of freezing injury and increases the need for an improved understanding of physiological responses to chilling and freezing temperatures. Abscisic acid (ABA) has been shown to increase during cold acclimation (CA) and play a role in dehydration tolerance. This study investigated changes in ABA metabolism and dehydrin expression during CA and their association with freezing tolerance in four bermudagrass cultivars. Two cold-tolerant (‘Patriot’ and ‘Riviera’) and two relatively cold-sensitive (‘Tifway’ and ‘Princess’) cultivars were either subjected to CA at 8 °C day/4 °C night with a light intensity of 250 μmol·m⁻²·s⁻¹ over a 10-h photoperiod for 21 days or maintained at 28 °C day/24 °C night over a 12-h photoperiod. In a separate study, exogenous ABA at 0, 50, 100, and 150 μm was applied to ‘Patriot’ bermudagrass without CA. ABA content in leaf and stolon tissues increased substantially during the first week of CA and remained relatively stable thereafter. ‘Patriot’ and ‘Riviera’ had greater ABA content and less stolon electrolyte leakage (EL) relative to ‘Tifway’ and ‘Princess’. Expression of a 25 kDa dehydrin protein increased during CA in all four cultivars. A significant correlation was found between ABA content and freezing tolerance. Exogenously applying ABA to ‘Patriot’ at 50, 100, and 150 μm significantly increased endogenous ABA content and the 25 kDa dehydrin expression and reduced stolon EL. The results suggest that alteration of ABA metabolism during CA is closely associated with freezing tolerance. Selection and use of cultivars with substantial accumulation of ABA and certain dehydrins during CA or in response to exogenous ABA could improve bermudagrass persistence in transition zone climates.

Zoysiagrass (Zoysia spp.), a warm-season turfgrass species, experiences freezing damage in many regions. The mechanisms of its cold acclimation and freezing tolerance have not been well understood. This study was designed to investigate effects of cold acclimation treatment on leaf abscisic acid (ABA), cytokinin (transzeatin riboside (t-ZR), and antioxidant metabolism associated with freezing tolerance in zoysiagrass (Zoysia japonica). ‘Chinese Common’ zoysiagrass was subjected to either cold acclimation treatment with temperature at 8/2 °C (day/night) and a photosynthetically active radiation (PAR) of 250 µmol·m⁻²·s⁻¹ over a 10-hour photoperiod or normal environments (temperature at 28/24 °C (day/night), PAR at 400 µmol·m⁻²·s⁻¹ and 14-hour photoperiod) for 21 days in growth chambers. Cold treatment caused cell membrane injury as indicated by increased leaf cell membrane electrolyte leakage (EL) and malondialdehyde (MDA) content after 7 days of cold treatment. Cold treatment increased leaf ABA and hydrogen peroxide content and reduced t-ZR content. Leaf superoxide dismutase (SOD), ascorbate peroxidase (APX) activity, and proline content increased, whereas catalase (CAT) and peroxidase (POD) activity declined in response to cold treatment. Cold treatment increased freezing tolerance as LT₅₀ declined from −4.8 to −12.5 °C. The results of this study indicated that cold acclimation treatment might result in increases in ABA and H₂O_2, which induce antioxidant metabolism responses and improved freezing tolerance in zoysiagrass.

Ethephon [ETH (2-chloroethylphosphonic acid, an ethylene-releasing compound)] has been used as a plant growth regulator in turfgrass management. The aim of the study was to assess the effects of ETH seed treatment on drought tolerance of kentucky bluegrass (Poa pratensis) seedlings. Seeds of two kentucky bluegrass cultivars, Midnight and Nuglade, were exposed to ETH treatment or untreated as controls. Seedlings were then exposed to two water regimes: well-watered conditions and polyethylene glycol (PEG)–induced drought conditions. ETH-treated plants exhibited better turf performance relative to the untreated control under PEG-stressed conditions illustrated by higher relative water content (RWC) and lower lipid peroxidation and lower electrolyte leakage (EL). In both cultivars, ETH treatment increased enzyme activity of ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT); proline content; and soluble protein content under PEG-induced drought conditions. The results suggest that ETH seed treatment can improve drought tolerance in kentucky bluegrass seedlings.

Creeping bentgrass (Agrostis palustris Huds.) is an extensively used cool-season grass for fine turf areas such as golf course putting greens, but suffers from poor summer stress tolerance. These studies were conducted to investigate the influences of natural plant growth regulators (NPGR) and Fe on creeping bentgrass photochemical activity (PA), antioxidant superoxide dismutase (SOD) activity, root growth and leaf color under two fertilization regimes. The bentgrass was maintained in well-watered field conditions or water-stressed glasshouse conditions. A mature bentgrass was treated monthly during the field season with seaweed (Ascophyllum nodosum Jol.) extract (SWE) at 50 mg·m^-2 or humic acid (HA) at 150 mg·m^-2 or in combination with or without FeSO₄ at 520 mg·m^-2 and grown under a low or a high fertilization regime. Foliar application of SWE + Fe increased PA (14% to 15%), while applications of SWE + HA or SWE + HA + Fe increased SOD activity (49% to 114%) of creeping bentgrass in Summer 1997 and Summer 1998. There was no significant fertilization × NPGR interaction for PA and SOD activity. Bentgrass PA was increased by 13% to 46% when treated with NPGR with or without Fe compared to the control measured in May. The addition of Fe with each NPGR application improved fall and winter leaf color. All NPGR and Fe treatments increased root mass (17% to 29%) in Aug. 1997 and 1998, except HA alone in 1998. Under sustained low soil moisture (-0.5 MPa) conditions, application of NPGR with or without Fe increased PA and SOD activity. The data indicate that SWE and HA enhance the physiological function of `Southshore' creeping bentgrass, resulting in improved root growth regardless of low or high fertilization regime. However, addition of Fe to these NPGR served primarily to improve late season leaf color. The results suggest that, in addition to maintaining adequate plant-available nutrients, applications of natural PGRs, such as SWE and HA, prior to and during summer abiotic stresses would be beneficial.

High ultraviolet-B (UV-B; 290-320 nm wavelength) radiation may significantly contribute to the quality decline and death of kentucky bluegrass (Poa pratensis L.) sod during summer transplanting. Antioxidants and protective pigments may be involved in plant defense against oxidative stress caused by UV-B. Selected exogenous hormones may alleviate UV-B damage by upregulating plant defense systems. The objectives of this study were to determine if exogenous hormone or hormone-like substances could alleviate UV-B damage to `Georgetown' kentucky bluegrass (Poa pratensis L.) under greenhouse conditions. The hormone salicylic acid at 150 mg·m^-2 and the hormone-containing substances, humic acid (HA) at 150 mg·m^-2 and seaweed extract (SWE) at 50 mg·m^-2, were applied to plugs of kentucky bluegrass and then subjected to UV-B radiation (70 μmol·m^-2·s^-1). The UV-B irradiation stress reduced turf quality by 51% to 66% and photochemical efficiency by 63% to 68% when measured 10 or 12 days after initiation of UV-B. Endogenous alpha-tocopherol (AT) and antioxidant enzymes (superoxide dismutase (SOD) and catalase) were reduced by UV-B stress. Anthocyanin content was increased from day 1 to 5 and then decreased from day 5 to 10 of continuous UV-B irradiation. Application of SA and HA + SWE enhanced photochemical efficiency by 86% and 82%, respectively, when measured 10 or 12 days after UV-B initiation. In addition, application of the hormonal supplements increased AT concentration, SOD, catalase activity, and anthocyanin content when compared to the control at 10 days after UV-B initiation. Bluegrass with greater AT concentration and SOD and catalase activity exhibited better visual quality under UV-B stress. The results of this study suggest that foliar application of SA and HA + SWE may alleviate decline of photochemical efficiency and turf quality associated with increased UV-B light levels during summer.

Plants possess various constitutive and inducible defense mechanisms such as pigment and antioxidant systems for protection against stresses such as ultraviolet-B (UV-B; 290 to 320 nm) radiation. Our previous research has indicated that higher chlorophyll, carotenoid, and anthocyanin concentrations were associated with greater tolerance of UV-B stress by `Georgetown' kentucky bluegrass (Poa pratensis L.). The objectives of this study were to determine if kentucky bluegrass cultivars with darker leaf color possessed greater pigment and antioxidant defense systems and if such increases were associated with greater resistance to UV-B. Eight cultivars exhibiting a range of green color intensity (`Apollo', `Brilliant', `Julius', Limerick', `Midnight', `Moonlight', `Nuglade', and `Total Eclipse') were selected and subjected to continuous, artificial UV-B radiation (70 μmol·m^-2·s^-1). UV-B irradiation reduced turf quality (55% to 62%) and photochemical efficiency (37% to 70%) when measured 5 days after initiation of UV-B exposure. Significant differences in turf color, photochemical efficiency, chlorophyll a, chlorophyll b, chlorophyll a+b, and carotenoids were found among the cultivars. `Moonlight' had greatest photochemical efficiency, chlorophyll, carotenoids, and turf quality. Positive correlations of pigment concentration with photochemical efficiency and turf color were observed under UV-B radiation stress, with correlation coefficients ranging from 0.49 to 0.62. The results of this study suggests that selecting cultivars with higher concentrations of chlorophyll and carotenoids and photochemical efficiency may be an effective way for turfgrass managers and sod producers to improve sod establishment and quality in environments with higher UV-B radiation.

Tall fescue is an important cool-season grass widely used for forage and turf, and its genotypic variation for morphological traits has not been well documented. One hundred and fifteen tall fescue accessions, including 25 commercial cultivars, were divided into five groups based on their origination. The morphological traits, including plant height, spike length, pulvinus distance, spikelet count, branch count per spike, spike count per plant, and spike weight in different accessions were determined under field conditions in 2013 and 2014. There was significant genotypic variation in morphological traits among the 115 tall fescue accessions. Wild accessions exhibited a greater variation in the morphological traits than commercial cultivars. Close correlations were found among plant height, spike length, pulvinus distance, and spikelet count. The results of this suggest plant height, spike length, pulvinus distance, and spikelet count could be used as key morphological traits for evaluating all fescue germplasm effectively.