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Ariana P. Torres and Roberto G. Lopez

seedlings requires an understanding of the effects of irradiance [photosynthetically active radiation (PAR) or photosynthetic photon flux ( PPF )] and temperature to manipulate plant growth and development ( Fausey and Cameron, 2005 ). Some desired

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T.J. Blom, M.J. Tsujita, and G.L. Roberts

Potted bulbs of Lilium longiflorum Thunb. `Ace' and `Nellie White' and Lilium (Asiatic hybrid) `Enchantment' were grown in a greenhouse under ambient photoperiod (APP), 8-h photoperiod by removing twilight from ambient by blackout cloth (8PP), or 8PP extended with 1 hour of low-intensity far-red radiation (9PP). Height of `Ace', `Nellie White', and `Enchantment' increased by 24%, 18%, and 12%, respectively, under APP and by 118%, 100%, and 44%, respectively, under 9PP compared to 8PP. In a second experiment, the effects of reduced irradiance (0%, 25%, 50%, and 75% shade) were determined on the same cultivars grown under APP or 8PP. The effects of APP on height were similar in magnitude for `Ace' and `Nellie White' but were insignificant for `Enchantment' compared to 8PP. Shading increased height linearly for all cultivars. The regression was greater under APP (2.8 mm/percent shade) than under 8PP (1.8 mm/percent shade) for `Ace' and `Nellie White' combined. Plant height of `Enchantment' was less affected by reduced irradiance. For all cultivars, APP or 9PP produced higher stem dry weight compared to 8PP. Shading decreased leaf and bulb dry weight of the Easter lily cultivars.

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Donald T. Krizek, Roman M. Mirecki, and Alton L. Fleming

A controlled-environment study was conducted in separate growth chambers with the wall surface covered either with white enamel paint (WEP) or polished aluminum (PA). `Williams' soybean were grown under 1500 mA cool white fluorescent lamps and internodes measured at 7, 14, and 21 days. Photosynthetic photon flux (PPF) levels in the center of each chamber were set at 320 μmol m-2 s-1 with a quantum sensor. Means ± SD for PPF levels in the WEP and PA chambers were 286 ± 28 and 307 ± 11 μmol m-2 s-1, respectively. This increase in mean PPF and decrease in variance of PPF in the PA chamber was reflected in: a) a decrease in hypocotyl, first internode, and total shoot elongation: and b) an increase in enlargement of the primary and the first trifoliolate leaves. These findings demonstrate that plants can detect small differences in irradiance within a growth chamber and suggest the advantages of using a highly polished wall surface to improve uniformity of irradiance and reduce variability in growth.

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Katherine F. Garland, Stephanie E. Burnett, Lois B. Stack, and Donglin Zhang

coggygria ‘Royal Purple.’ Sci. Hort. 71 59 66 Pennisi, S. van Iersel, M.W. Burnett, S.E. 2005 Photosynthetic irradiance and nutrition effects on growth of English ivy in subirrigation systems HortScience 40 1740 1745 Pramuk, L.A. Runkle, E.S. 2005

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Kirk W. Pomper, Desmond R. Layne, and Snake C. Jones

The North American pawpaw [Asimina triloba (L.) Dunal] has great potential as a fruit crop or as a landscape plant. The influence of incident irradiance on pawpaw seedling growth and development in containers was examined in the greenhouse and outdoors. Root spiraling can be a problem for container-grown pawpaw seedlings; therefore, the influence of paint containing cupric hydroxide [Cu(OH)2] at 100 g·L-1 applied to the interior of containers on plant growth was also examined in a greenhouse environment. In pawpaw seedlings grown outdoors for 11 weeks, low to moderate shading levels of 28%, 51%, or 81% increased leaf number, total leaf area, and total plant dry weight (DW) compared to nonshaded seedlings. A shading level of 81% decreased the root to shoot ratio by half compared to nonshaded plants. Shading of 98% reduced leaf number, leaf size, and shoot, root, and total plant DW. Shading increased leaf chlorophyll a and b concentrations for pawpaw seedlings grown outdoors, while it decreased average specific leaf DW (mg·cm-2). In a separate greenhouse experiment, pawpaw seedlings subjected to shade treatments of 0%, 33%, 56%, 81%, or 98% did not respond as greatly to shading as plants grown outdoors. Greenhouse-grown plants had greater total and average leaf area under 33% or 56% shading than nonshaded plants; however, shading >56% reduced root, shoot, and total plant DW. Total shoot DW was greater in greenhouse grown plants with 33% shading compared to nonshaded plants. Pawpaw seedlings in control and most shade treatments (33% to 81%) in the greenhouse environment had more leaves and greater leaf area, as well as larger shoot, root, and total plant DW than seedlings in similar treatments grown outdoors. The greenhouse environment had a 10% lower irradiance, a 60% lower ultraviolet irradiance, and a significantly higher (1.23 vs. 1.20) red to far-red light ratio than the outdoors environment. Treatment of container interiors with Cu(OH)2 decreased total and lateral root DW in nonshaded seedlings, and it adversely affected plant quality by causing a yellowing of leaves and reduction of chlorophyll levels by the end of the experiment in shaded plants. Growth characteristics of pawpaw seedlings were positively influenced by low to moderate shading (28% or 51%) outdoors and low shading (33%) in the greenhouse. Seedlings did not benefit from application of Cu(OH)2 to containers at the concentration used in this study. Commercial nurseries can further improve production of pawpaw seedlings using low to moderate shading outdoors.

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Grace M. Pietsch, William H. Carlson, Royal D. Heins, and James E. Faust

The effects of day and night temperatures (15 to 35C) and three irradiance levels [50% of ambient, ambient, and ambient plus 12 mol·m-2·day-1 of supplemental photosynthetic photon flux (PPF)] on development of Catharanthus roseus `Grape Cooler' were determined. Time to flower decreased by 30 days and leaf-pair unfolding rate (LUR) increased linearly as average daily temperature increased from 18 to 35C. Flower size was greatest when plants were grown at 25C. Supplemental light decreased days to flower and increased flower size. Flowering occurred when nine leaf pairs were present on the plant. Using the inverse of the LUR curve, i.e., days per leaf pair, the number of days to flower could be predicted at any time during plant development based on plant leaf number.

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John Erwin, Esther Gesick, Ben Dill, and Charles Rohwer

The impact of photoperiod, irradiance, and/or cool temperature on flowering and/or dormancy in Mamillopsis senilis and Echinopsis and Trichocereus hybrids was studied. Two- to 3-year-old plants (180 plants of each type) were grown for 4 months under natural daylight (DL) conditions (August–November) in a greenhouse maintained at 26 ± 2 °C. Plants were then placed in either of two greenhouses: a cool temperature house (5 ± 2 °C; DL), or a lighting treatment house (22/18 ± 1 °C day/night temperature, respectively). The lighting treatment house had eight light environments: 1) short day (SD; 8 h; 0800–1600 hr); 2) SD+25–35 μmol·m-2·s-1; 3) SD+45–50 μmol·m-2·s-1; 4) SD+85–95 μmol·m-2·s-1; 5) DL plus night interruption lighting (NI; 2200–0200 hr; 2 μmol·m-2·s-1 from incandescent lamps); 6) DL+25–35 μmol·m-2·s-1 (lighted from 0800–0200 hr); 7) DL+45–50 μmol·m-2·s-1; and 8) DL+85–95 μmol·m-2·s-1. Supplemental lighting was provided using high-pressure sodium lamps. Plants were placed in the cool temperature house for 0, 4, 8 or 12 weeks before being placed under lighting treatments. All plants received lighting treatments for 6 weeks and were then placed in a finishing greenhouse (DL; 22 ± 2 °C). Data were collected on approximate day when growth resumed, the date when each flower opened (five only), total flower number per plant, and how long each flower stayed open (five only). Whether species exhibited dormancy and what conditions, if any, broke that dormancy was identified. Species were also classified into photoperiodic, irradiance, and vernalization response groups with respect to flowering.

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Marvin Pritts and Dorcas Isuta

Previous findings reveal that rooting and acclimatization of apple and blueberry plants is often difficult, inconsistent and inefficient. This experiment was set up in a fog chamber lo investigate the effects of CO2 enrichment (CDE) and irradiance on unrooted stage II microshoots. Two CO2 and 3 light levels tested were: 1350 +/- 150 (+ CDE), and 450 +/- 50 (- CDE) ppm; 30 +/- 5 (low), 55 + 10 (medium), and 100 + 20 (high) umolm-2s-1 respectively. Cultivars assessed were Berkeley and Northsky for blueberry. G65 and NY30 for apple. Blueberry microshoots acclimatized successfully and gave between 90 to 100% rooting and survival rate. Apple microshoots acclimatized and rooted slowly, exhibited great sensitivity to in vivo conditions and gave between 40 to 100% rooting and survival rate. High light induced photo-inhibition which disappeared after complete acclimatization. There was a significant difference between low light and the other two light levels. The effect of CDE was dependent on cultivar. In most cases, high light (-) CDE gave the most vigorous growth (highest plant dry weight and leaf area). There was a significant difference between (+) CDE and (-) CDE at low and medium light, but none at high light. Low light (-) CDE and medium light (+) CDE were superior over low light (+) CDE and medium light (-) CDE. respectively. Stalling out in apple microshoots was corrected by GA sprays.

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Fouad M. Basiouny

Blueberry fruits (Vaccinium ashie Read) of two cultivars, `Delite' and `Woodard', were hand-picked twice during the growing season (15 June and 1 July) to study the benefits of UV-B irradiance on postharvest fruit quality. After precooling, healthy, disease-free, uniform fruits were selected and exposed to UV-B irradiance (180 to 310 nm) for 24 h under cold conditions. The fruits were then kept at 2–3 °C and 90% to 95% relative humidity for 2 weeks before determining their quality parameters. Irradiated fruits were softer, wrinkled, and non-marketable compared to non-irradiated berries. UV-B had no beneficial effects on fruit quality or storability.

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Jirong Jiao and Bernard Grodzinski

Photosynthesis and concurrent export rates of expanded leaves on the flowering shoot of Rosa hybrida L. `Samantha' were measured at three stages of shoot and flower bud development. At 35 and 90 Pa CO2 photosynthesis and concurrent export rates of the upper expanded leaves were greater at Stage 3 (i.e., when petal color of the flower bud was visible) than at the two earlier stages of shoot and flower development. The optimum for leaf photosynthesis and concurrent export at ambient CO2 and saturating irradiance were ≈25 °C. Export was more sensitive to increased temperature than was carbon fixation. For example, at 40 °C photosynthesis was 40% lower while the export rate during photosynthesis was reduced by 80%. Increasing the photon fluence flux rate from 200 to 1000 μmol·m-2·s-1 PAR increased the photosynthetic rate and the concurrent export rate at 35 and 90 Pa CO2, but the increase in export was proportionally greater than that of photosynthesis. At 35 Pa CO2, the rate of C export during photosynthesis increased from 31 to 59% of the concurrent C fixation rate. At 90 Pa CO2, export during photosynthesis increased from 38 to 62% of the photosynthesis rate. The importance of irradiance on translocation processes was further demonstrated by comparing the disappearance of label during the feed period and during an extended night period. Plants grown at each CO2 level exported about three times as much of the 14C fixed during a 2-hour feed period in the light as during a subsequent 15-hour dark chase period. The nighttime export and respiration rates of leaves which had been exposed to elevated CO2 levels during the feed were higher than those rates observed at ambient CO2. However, at the end of the chase period, the leaves of plants which had been exposed to CO2 enrichment during the feed also retained more 14C than did the leaves of the plants which were at ambient CO2. Thus, although more 14C was fixed and exported under high CO2, the same proportion of labelled assimilates were exported, respired, and retained in the dark as at ambient CO2.