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Rong Zhang, Zhubing Yan, Yikun Wang, Xuesen Chen, Chengmiao Yin, and Zhiquan Mao

antioxidant enzyme activity. SOD activity was measured by the nitroblue tetrazole method, POD activity was measured by the guaiacol method, CAT activity was measured by the ultraviolet absorption method, and APX activity was measured by the colorimetric method

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Sanalkumar Krishnan, Yingmei Ma, and Emily Merewitz

hormonal responses for the promotion of turfgrass science research and management. Materials and Methods Plant material and growth conditions. Sod plugs of creeping bentgrass were harvested from the Hancock Turfgrass Research Center in East Lansing, MI

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S.M. Lutfor Rahman, Wayne A. Mackay, Eiji Nawata, Tetsuo Sakuratani, A.S.M. Mesbah Uddin, and Bruno Quebedeaux

Effects of water stress on superoxide dismutase (SOD) activities, changes in protein content, leaf water potential (Ψl) and growth were studied in drought-sensitive Kyokko (KK) and Ratan (RT), and drought-tolerant TM 0126 (TM) and VF-134-1-2 (VF) cultivars of tomato (Lycopersicon esculentum Mill.) in order to obtain fundamental information for breeding drought tolerant cultivars that may be adapted to water stress in many parts of the world. Growth of drought-tolerant TM and VF was greater than that of drought-sensitive KK and RT under water stress conditions. Leaf water potential (Ψl) decreased by water stress treatments in all the cultivars, but the reduction was much more rapid and pronounced in KK and RT than VF and TM. Ψl of stressed cultivars decreased by 30% to 40% compared to the untreated control cultivars. The initial reduction in the range of 20% to 35% was more rapid in KK and RT than TM and VF. SOD activities were increased by water stress in all cultivars. Increase of SOD activities by water stress was much more rapid and pronounced in TM and VF than in KK and RT. Leaf protein concentration was decreased by the water stress treatments in all cultivars evaluated. In KK and RT, much more rapid reductions in protein concentration were observed than in TM and VF. The regression analysis of Ψl and SOD suggest the possibility to using SOD activities as an additional screening criterion for tomato drought tolerance improvement.

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Xunzhong Zhang and R.E. Schmidt

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).

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Xunzhong Zhang, E.H. Ervin, and R.E. Schmidt

Ultraviolet-B [UV-B (280-320 nm)] radiation is one of the major factors causing quality decline of transplanted sod. Pigments and antioxidants are associated with plant stress resistance, but their roles in turfgrass tolerance to UV-B damage are not well understood. The objectives of this study were to determine if kentucky bluegrass (Poa pratensis L.) cultivars with darker green genetic leaf color possessed greater pigment and antioxidant defense capacities and if such characteristics were associated with greater resistance to UV-B. Two cultivars, `Moonlight' (dark green) and `Limerick' (light green), were selected and subjected to continuous, artificial UV-B radiation (70 μmol·m-2·s-1). UV-B irradiation reduced turf quality by 58% (`Moonlight') and 77% (`Limerick') relative to day 1 when measured 10 days after initiation of UV-B exposure. Higher canopy photochemical efficiency (PEc) was found in `Moonlight' relative to `Limerick' under UV-B stress and during recovery. `Moonlight' contained greater levels of chlorophyll (1.5 to1.6-fold), carotenoids (1.3-fold), superoxide dismutase [SOD (1.0-fold)] and catalase [CAT (1.5-fold)] than `Limerick' when measured at 10 days after UV-B initiation. Turfgrass quality and PEc were positively correlated with pigments (chlorophyll and carotenoids) and antioxidant enzymes (SOD and CAT), and negatively correlated with lipid peroxidation. The results suggest that selecting dark-green cultivars with greater pigment content and antioxidant activity may be an effective approach for turfgrass breeders and sod producers to improve tolerance of newly transplanted sod to environments with higher UV-B radiation.

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Shengrui Yao, Ian A. Merwin, and Michael G. Brown

treatments of glyphosate applied at a rate of 2 kg·ha −1 a.i. in mid-May and July each year; 3) mowed sod (Grass): Red fescue ( Festuca rubra L.) turfgrass originally seeded in Sept. 1991, now a mixture of ≈20 grass and herbaceous broadleaf species mowed

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W.G. Foshee, W.D. Goff, K.M. Tilt, J.D. Williams, J.S. Bannon, and J.B. Witt

Organic mulches (leaves, pine nuggets, pine straw, grass clippings, and chipped limbs) were applied at depths of 10, 20, or 30 cm in a 3 × 3-m area around young pecan [Carya illinoinensis (Wangenh.) K. Koch] trees. These treatments were compared to an unmulched herbicide treatment and a common bermudagrass [Cynodon dactylon (L.) Pers.] sod. Trunk cross-sectional areas (TCSAs) of the mulched trees were larger than those of trees in the sod or unmulched plots and increased linearly as mulch depth increased. All mulches influenced TCSA similarly. Mean TCSA for mulched trees increased 14-fold compared to an increase of 8-fold for the unmulched trees and the sod in this 3-year study. Thus, common yard-waste mulches can be used effectively to increase growth of young pecan trees.

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Dean R. Evert and Paul F. Bertrand

More peach [Prunus persica (L.) Batsch.] trees survived when planted in killed bahiagrass (Paspalum notatum Flugge `Paraguayan-22') sod growing between previous orchard tree rows (98%) than when planted in previous tree sites (81%) or in previous tree rows, but halfway between previous tree sites (79%). The previous orchard was removed Nov. 1986, and new trees were planted Feb. 1987. Surviving trees in the killed sod grew better than trees at the other two sites. Tilling the sites before planting did not affect nematode populations or tree survival and growth. Soaking the tree roots in a fenamiphos solution (1 g·liter-1) for 20 minutes before planting resulted in 79% tree survival vs. 93% survival for the nonsoaked trees. Fenamiphos sprayed under the trees at a rate of 11.2 kg·ha-1 during the spring and fall of the planting year did not change nematode populations, tree survival, or tree growth. The fenamiphos sprays reduced the increase in trunk cross-sectional area by 3 cm2 for trees in the sod. Other than leaf Zn concentration, which was low, concentrations of the elements were within the sufficiency range for Georgia for all treatments. Trees planted in the killed sod had an increased leaf K concentration and decreased leaf Mg concentration when compared with trees planted in the rows. Chemical name used: ethyl 3-methyl-4-(methylthio)phenyl (1-methylethyl)phosphoramidate (fenamiphos).

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Martin Paré and Deborah Buszard

Four soil management treatments were applied from 1991 to 1993 to `Spartan'/M.9 apple trees planted in 1987. Geotextile, straw mulch, composted manure mulch, and grass sod were used to control weed growth in a 1-m-wide band under the trees. The experiment was a randomized complete block design with two blocks and seven trees per treatment; data was taken from the five inner trees in each plot. Trees in straw mulch showed the largest increase in trunk cross-sectional area (+45.6%) over the three years; those in the geotextile showed the second largest (40.7%). Straw mulch also resulted in the largest yield 2 years out of 3. Fruit set and fruit quality were also assessed, and trees in manure mulch and grass sod set the least fruit in each season. Fruit from the grass sod treatment remained harder in storage, and both straw mulch and grass sod have a higher proportion of grade A fruit (57 of total fruit).

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Neil L. Heckman, Garald L. Horst, Roch E. Gaussoin, and Linda J. Young

Heat accumulation during storage of sod may reach lethal temperatures within 4 days, decreasing sod quality. Treatment with trinexapac-ethyl reduces heat accumulation during sod storage. However, heat tolerance of grasses treated with trinexapacethyl has not been documented. Our objectives were to: 1) determine the lethal temperatures for Kentucky bluegrass (Poa pratensis L.); and 2) identify the effect of a single application of trinexapac-ethyl on heat tolerance. Experimental design was a randomized complete block with three replications and a two (trinexapac-ethyl vs. control) × two (cultivars) factorial arrangement of treatments. Ten days after chemical treatment, Kentucky bluegrass sprigs were exposed to heat stress for 4 days in a temperature gradient block under low vapor pressure deficit. Treatment with trinexapac-ethyl at 0.23 kg·ha-1 reduced heat tolerance. Temperature needed to kill 50% of the population was 35.5 °C for treated vs. 36.1 °C for nontreated grass. Trinexapac-ethyl is in the same chemical family as the cyclohexanedione herbicides that interfere with lipid syntheses in grasses. This may be a reason for the slight decrease in heat tolerance. The practical value of trinexapac-ethyl treatment in reducing heat accumulation during storage of sod may be partially negated by a decrease in heat tolerance. Chemical name used: [(4-cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid methyl ester] (trinexapac-ethyl).