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Yaling Qian and Jack D. Fry

Greenhouse studies were conducted on three warm-season turfgrasses, `Midlawn' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], `Prairie' buffalograss [Buchloe dactyloides (Nutt.) Engelm.], and `Meyer' zoysiagrass (Zoysia japonica Steud.), and a cool-season turfgrass, `Mustang' tall fescue (Festuca arundinacea Schreb.) to determine 1) water relations and drought tolerance characteristics by subjecting container-grown grasses to drought and 2) potential relationships between osmotic adjustment (OA) and turf recovery after severe drought. Tall fescue was clipped at 6.3 cm once weekly, whereas warm-season grasses were clipped at 4.5 cm twice weekly. The threshold volumetric soil water content (SWC) at which a sharp decline in leaf water potential (ψL) occurred was higher for tall fescue than for warm-season grasses. Buffalograss exhibited the lowest and tall fescue exhibited the highest reduction in leaf pressure potential (ψP) per unit decline in ψL during dry down. Ranking of grasses for magnitude of OA was buffalograss (0.84 MPa) = zoysiagrass (0.77 MPa) > bermudagrass (0.60 MPa) > tall fescue (0.34 MPa). Grass coverage 2 weeks after irrigation was resumed was correlated positively with magnitude of OA (r = 0.66, P < 0.05).

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Gene E. Lester, John L. Jifon and D. J. Makus

Netted muskmelon [Cucumis melo L. (Reticulatus Group)] fruit quality (ascorbic acid, β-carotene, total free sugars, and soluble solids concentration (SSC)) is directly related to plant potassium (K) concentration during fruit growth and maturation. During reproductive development, soil K fertilization alone is often inadequate due to poor root uptake and competitive uptake inhibition from calcium and magnesium. Foliar applications of glycine-complexed K during muskmelon fruit development has been shown to improve fruit quality, however, the influence of organic-complexed K vs. an inorganic salt form has not been determined. This glasshouse study investigated the effects of two K sources: a glycine-complexed K (potassium metalosate, KM) and potassium chloride (KCl) (both containing 800 mg K/L) with or without a non-ionic surfactant (Silwet L-77) on melon quality. Orange-flesh muskmelon `Cruiser' was grown in a glasshouse and fertilized throughout the study with soil-applied N–P–K fertilizer. Starting at 3 to 5 d after fruit set, and up to 3 to 5 d before fruit maturity at full slip, entire plants were sprayed weekly, including the fruit, with KM or KCl with or without a surfactant. Fruit from plants receiving supplemental foliar K had significantly higher K concentrations in the edible middle mesocarp fruit tissue compared to control untreated fruit. Fruit from treated plants were also firmer, both externally and internally, than those from non-treated control plants. Increased fruit tissue firmness was accompanied by higher tissue pressure potentials of K treated plants vs. control. In general, K treated fruit had significantly higher SSC, total sugars, total ascorbic acid, and β-carotene than control fruit. Fall-grown fruit generally had higher SSC, total sugars, total ascorbic acid and β-carotene concentrations than spring-grown fruit regardless of K treatment. The effects of surfactant were not consistent but in general, addition of a surfactant tended to affect higher SSC and β-carotene concentrations.

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Xue-Min Hou, Zi-Hua Wang, Xi-Min Deng and Guo-Hui Li

The P-V curve has been used to estimate symplastic water volume, ψ S , pressure potential, turgor loss point, and elastic modulus of plant cells, tissue, and organs ( Holbrook and Sinclair, 1992 ; Richter, 1978 ; Scholander et al., 1965 ; Tyree

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Mason T. MacDonald, Rajasekaran R. Lada, Martine Dorais and Steeve Pepin

xylem pressure potential (XPP) in balsam fir decreases after harvest and is negatively correlated with needle retention ( MacDonald, 2010 ), but these studies did not directly explore the link between water status and ethylene evolution. If decreased

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Mason T. MacDonald, Rajasekaran R. Lada, Alex I. Martynenko, Martine Dorais, Steeve Pepin and Yves Desjardins

., 2009 , 2010 ). Average water use. Average daily water use (mL·g −1 ·d −1 ) was determined gravimetrically using the following equation: Xylem pressure potential. The XPP of branches was measured after 14 d using a Plant Moisture System Pressure Bomb

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D.M. Glenn and W.V. Welker

Seedling `Tennessee Natural' peach [Prunus persica (L.) Batsch] trees were grown in a series of five greenhouse experiments to determine how peach root development was affected by the interaction of soil pressure potential and the presence of Kentucky-31 (K-31) tall fescue (Festuca arundinaceae Schreb.). Peach trees were grown in split-root rhizotrons that had four separate root growth sections. When two of the four sections had live sod (LS) and two remained bare soil (BS), there was no effect of the LS on peach root development when the trees were irrigated daily. Peach root development was reduced in BS and LS treatments when soil pressure potential was less than -0.06 MPa. In contrast, when trees were grown in rhizotrons that had all four sections with either LS or a killed K-31 sod (KS), peach root development was reduced in the LS treatment compared to the KS treatments when irrigated daily or when soil pressure potential reached -0.03 MPa. The apparent root surface water potential of peach trees in the LS treatment was -0.4 MPa lower than that in the KS treatment under daily irrigation due to the interference of the K-31 tall fescue. In two additional experiments using peach trees with BS in all four sections, we maintained three sections at field capacity and allowed one section to dry to -0.06 to 1.5 MPa. During the night, when transpiration was low, water was transferred to the dry soil section via the peach root system from the three wet soil sections. It appears that the root system of peach can maintain root development in the presence of tall fescue by transferring water from regions of high water availability to those of low availability.

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L. Eric Hinesley and Layne K. Snelling

Postharvest drying of Leyland cypress [× Cupressocyparis leylandii (A.B. Jacks. & Dallim.)] branches was intermediate between eastern red cedar (Juniperus virginiana L.) and Fraser fir [Abies fraseri (Pursh) Poir.] in two laboratory experiments. Leyland cypress rehydrated without adverse effect until xylem pressure potential reached –4.0 to –5.0 MPa (shoot moisture content = 60% to 65%). For branches continuously maintained in water, Fraser fir and Leyland cypress kept equally well over 4 weeks of display, but Leyland cypress lasted longer than Fraser fir over 8 weeks. Postharvest keeping quality of Leyland cypress and Fraser fir was better than that of eastern red cedar.

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Ricky M. Bates, James C. Sellmer and David A. Despot

Needle retention, xylem pressure potential and overall quality of canaan fir (Abies balsamea var. phanerolepis (L.) Mill.) and fraser fir (Abies fraseri (Pursh) Poir.) Christmas trees were evaluated over a 40-day display period. Cut trees were stored outdoors for 24, 48, or 96 hours, and half the trees had a 2.5-cm section trimmed from the basal portion of the stem, before placement in water at an indoor display room. Controls were placed in water immediately after harvest. Xylem pressure potentials and overall quality were similar for both species except for trees stored 96 hours. Untrimmed canaan fir dried to -2.4 MPa and was rated below average by the end of the display period compared to -1.3 MPa and a good quality rating for fraser fir. Needle retention and color characteristics were excellent across all treatments for fraser fir during the entire display period. Needle loss for canaan fir began relatively soon during display, generally increased across all treatments, and was highly variable. In addition, quality of some canaan fir trees decreased as needles turned brown, but did not shed during the display period. Tree water status alone did not completely account for loss of needles and quality in canaan fir; the need exists to identify seed sources with better postharvest characteristics.

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Gary A. Chastagner and Kathleen L. Riley

Moisture and needle loss characteristics were similar for noble (Abies procera Red.) and Nordmann fir [Abies nordmanniana (Stev.) Spach.] Christmas trees that were displayed in water. After 42 days, trees still had xylem pressure potentials above -2 MPa. In addition, trees that were displayed in water had very little needle loss. When trees were displayed dry, noble and Nordmann fir had similar rates of moisture loss, drying to about -6 MPa in about 3 weeks. Although there was very little needle loss from any of the noble fir trees that were displayed dry, some Nordmann fir trees began to shed large numbers of green needles within 3 to 5 days, which significantly reduced postharvest quality. Unless sources of Nordmann fir are identified that have good needle retention characteristics, the needle loss problem observed when trees dry to about -3 MPa has the potential to limit the use of this species as a Christmas tree in the United States.

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Rita L. Hummel

Four film-forming antitranspirants, Vapor Gard, Envy, Wilt-Pruf, and Folicote, and a new metabolic antitranspirant UC86177 were applied to container-grown Ulmus parvifolia Jacq. (Chinese elm), Malus sargentii Rehd. (Sargent's crabapple), Viburnum plicatum tomentosum Thunb. (doubleflle viburnum), Lycopersicon esculentum Mill. `Early Giant' (tomato), Petunia × hybrids Hort. Vilm-Andr. `Royal Pearls' (petunia), and Impatiens wallerana Hook. f. `Blitz Orange' (impatiens) plants. Water status was assessed by the following methods: transpiration as water loss per unit leaf area, wilt by visual evaluation, and xylem pressure potential (XPP) determined with a pressure chamber. Antitranspirant treatment had no beneficial effect on water status of doublefile viburnum. In comparison to control plants, results of wilt ratings, XPP, and transpiration measurements for the elm, crabapple, tomato, petunia, and impatiens plants can be summarized as follows: UC86177-treated plants showed significantly less stress in 11 measures and were not different once; Wilt-Pruf was beneficial 10 times and not different twice; Folicote was beneficial nine times and not different three times; Vapor Gard produced eight beneficial results and four similar results; and Envy was beneficial three times and no different nine times. Species differences in response to antitranspirants as well as differences in product efficacy were demonstrated. UC86177 antitranspirant was shown to be as or more effective in controlling water status than the film-forming antitranspirants and may have potential for protecting various plant species against water stress.