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Zhou Li, Yan Peng, and Bingru Huang

). Chlorophyll content was calculated using the formula described by Arnon (1949) . A chlorophyll fluorescence meter (Fim 1500; Dynamax, Houston, TX) was used for measuring photochemical efficiency (F v /F m ). Individual leaves were adapted to darkness for 30

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Zhou Li, Yan Peng, and Bingru Huang

, leaves extractions were measured at 663 and 645 nm using a spectrophotometer (Spectronic Instruments, Rochester, NY) ( Arnon, 1949 ). For photochemical efficiency (Fv/Fm), leaves were pretreated into darkness through leaf clips for 20 min. Fv/Fm ratio was

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Qingqing Duan, Ye Lin, Wu Jiang, and Danfeng Huang

fluorescence (F m ) were measured after dark adaptation for 30 min. The maximal photochemical efficiency of PSII (F v /F m ) was calculated as F v /F m = (F m – F o )/F m . During illumination, the steady-state fluorescence (F s ) was obtained. The light

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Shuyang Zhen and Marc W. van Iersel

correspondingly a high rate of carbon assimilation and plant growth, is achieved at the expense of photochemical efficiency (also see van Iersel et al., 2016b ). Consistent with the higher Φ PSII observed in sweetpotato and in plants grown under full sun, ETR at

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Giverson Mupambi, Stefano Musacchi, Sara Serra, Lee A. Kalcsits, Desmond R. Layne, and Tory Schmidt

fluorescence and leaf spectral reflectance. Chlorophyll fluorescence was measured using a pulse modulated, chlorophyll fluorometer, (OS1p; Opti-Sciences, Hudson, NH). The maximum photochemical efficiency of PSII (F v /F m ) was measured by dark adapting leaves

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Sanalkumar Krishnan and Emily B. Merewitz

yield of regulated nonphotochemical energy loss in photosystem II (YII) and photochemical efficiency (F v /F m ) were measured on attached leaves with two subsamples per plant using a fluorimeter instrument (OSp5; Opti-Sciences, Hudson, NH). Osmotic

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E.H. Ervin, Xunzhong Zhang, J.M. Goatley Jr., and S.D. Askew

Creeping bentgrass (Agrostis stolonifera) is used extensively on temperate zone golf course greens, tees, and fairways, but often performs poorly in shade. Previous research has indicated that sequential applications of gibberellic acid (GA) inhibiting plant growth regulators (PGRs) such as trinexapac-ethyl (TE) increase cool-season turfgrass performance in 70-90% shade. This research was conducted to: 1) confirm appropriate TE application rates and frequencies for maintaining `Penncross' creeping bentgrass in dense shade in the mid-Atlantic region of the U.S.; 2) determine the efficacy of other PGRs, biostimulants, and iron (Fe); and 3) assess whether the addition of a biostimulant with TE would have additive, synergistic, or negative effects. The other compounds tested against TE and the control were: propiconazole (PPC), iron sulfate, CPR (a seaweed and iron containing biostimulant), and a generic seaweed extract (SWE) (Ascophyllum nodosum) plus humic acid (HA) combination. These treatments were applied to 88% shaded bentgrass every 14 days from May or June through October in 2001 and 2002, with turf quality, leaf color, root strength, photochemical efficiency, and antioxidant enzyme superoxide dismutase (SOD) activity being determined. While the quality of control plots fell below a commercially acceptable level by the second month of the trial, repeated foliar TE application provided 33% to 44% better quality throughout the experiment. Propiconazole resulted in 13% to 17% better quality through September of each year. Trinexapac-ethyl and PPC resulted in darker leaf color and increased mid-trial root strength by 27% and 29%, respectively. Canopy photochemical efficiency and leaf SOD activity were also increased due to TE in August of both years. Treatment with Fe, CPR, or SWE+HA did not have an effect on quality, root strength, SOD, or photochemical efficiency, but periodic increases in color were observed. The addition of CPR to TE in 2002 provided results that were not different from those of TE-alone. This and previous studies indicate that restricting leaf elongation with anti-GA PGRs is of primary importance for improving shade tolerance, while treatments that increase leaf color or chlorophyll levels without restricting leaf elongation are relatively ineffective.

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Thomas E. Marler and Patrick J. Lawton

Leaflets of carambola were restricted to a horizontal position for 3.5-h during late morning and early afternoon on sunny days to determine the influence of natural leaflet movement on temperature and chlorophyll fluorescence. Adaxial temperature of these horizontal leaflets was 5-9 C higher than that of leaflets that were allowed to move in response to high light. Chlorophyll fluorescence was similarly affected. Leaflets that were allowed to move had a higher Fv/Fm than leaflets that were restricted in movement The results indicate that the presence of a pulvinus at the base of each leaflet of carambola leaves allows movement of the leaflet to avoid incident light. This natural leaflet movement under sunny conditions results in a lower temperature and a higher level of photochemical efficiency when compared with leaflets that are exposed to high light due to restricting their movement.

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Sorkel Kadir, Said Ennahli, and Ben Glass

Interactive effects of different temperature regimes and anti-transpiration organic materials, Surround WP (kaolinite clay) and Raynox (sun-protectant), on two strawberry (Fragaria ×ananassa) cvs. Chandler and Sweet Charlie were investigated under controlled environmental conditions. Newly planted strawberries treated with Surround and Raynox were subjected to 20/15, 30/25, and 40/35 °C (day/night) temperature regimes and 16 day/8 night photoperiod in growth chambers for 42 d. Photosynthesis (A) and photochemical efficiency (Fv/Fm) were measured at 7-d intervals during the experiment. Plants treated with Raynox displayed greater resistance to high temperature (40/35 °C) compared to those treated with Surround. Net photosynthesis of both cultivars decreased significantly with time at 40/35 °C. There was no significant difference in photosynthetic rate between the two cultivars. Nevertheless, there was difference in plant biomass between the cultivars. Raynox provided more protection against high temperature, specifically in reducing stomatal conductance and limiting transpiration, than Surround.

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William R. Nail and G. Stanley Howell

Potted grapevines (Vitis vinifera L. `Chardonnay') were inoculated with conidial suspensions of the grapevine pathogen causing powdery mildew of grape (GPM) (Uncinula necator (Schw.) Burr.). Leaves of inoculated and noninoculated vines were studied for the effects of varying light (PAR) and CO2 concentrations on factors affecting carbon assimilation. GPM reduced carboxylation efficiency (k), net CO2 assimilation rate (A), stomatal conductance (g s), and internal CO2 concentration (Ci) under ambient CO2, A max at >900 ppm CO2, stomatal limitations to A (lg), and photochemical efficiency (Φ) on diseased leaves, while having no effect on the CO2 compensation point (Γ) or the light compensation point (cp). GPM had no significant effect on chlorophyll fluorescence (Fv/Fm).