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Angela R. Beaman, Richard J. Gladon, and James A. Schrader

capacity to produce sufficient edible biomass within the lowest possible area, volume, and energy inputs such as irradiance. Salad crops such as lettuce ( Lactuca sativa L.) have been selected for use in extraterrestrial food-production facilities and the

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Domenica Scuderi, Francesco Giuffrida, Stefania Toscano, and Daniela Romano

treatments were defined by a factorial combination of five shading levels (0%, 20%, 40%, 60%, and 80% reduction of the incident irradiance inside the greenhouse) and two growth periods, specifically, from May to October (GP I) and from December to May (GP II

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Desmond G. Mortley, Stephanie Burrell, Conrad K. Bonsi, Walter A. Hill, and Carlton E. Morris

addition to irradiance, daily light period also influences the growth and yield of sweetpotatoes. As part of the Exploration Life Support System program, NASA testing has focused on light period responses of candidate species, the rationale being that if

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Woei-Jiun Guo, Yu-Zu Lin, and Nean Lee

irradiance is often a key factor for maximal photosynthesis. In Phalaenopsis , low irradiance significantly slows the growth rate at all developmental stages and delays flower formation as well as reduces flower count ( Lee, 2000 ; Lin and Lee, 1998 ; Wang

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Jennifer K. Boldt

( Blanchard et al., 2011 ; Miller and Armitage, 2002 ; Niu et al., 2000 ). However, few studies have looked at the impact of a reduction in the mean weekly temperature (MWT) in conjunction with fluctuating daily temperatures. Irradiance is a primary driver

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Martin P.N. Gent

according to RGR? To what extent are these determined by irradiance or time of year and by conditions of the nutrient solution in hydroponics? Irradiance is the primary factor affecting RGR ( Gent, 2014 ). However, a function of light intercepted by the crop

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H. Biesinger, W.F. Campbell, T. Strickland, F.B. Salisbury, P.S. Hole, L. Gillespie, M. Levinskikh, and I. Ivanova

The objectives of this research were to mimic the gradient irradiances to which wheat (Triticum aestivum L. cv. SuperDwarf) plants were exposed aboard the Russian space station Mir, and to determine whether these irradiances inhibit growth and floral development. SuperDwarf wheat plants were exposed to irradiances of 20–40, 60–80, 100–120, and 140–180 (PPF = μmol·cm–2·s–1) and grown to maturity. Twenty plants were randomly selected from each irradiance level and chlorophyll, total leaf area, shoot biomass, and total soluble leaf and plasma membrane (PM) proteins were recorded. Irradiance at increasing levels of intensity increased the fresh biomass, leaf area, chlorophyll content, and the total soluble PM and leaf proteins of wheat tissue. There were significant differences between the abaxial and adaxial sides of the wheat leaves in stomatal density, stomatal index, stomatal length and width, and number of stomata along 1-mm length of leaf. These data may be uniquely valuable for further studies of relationships between chlorophyll content, photosynthetic rate, and productivity of wheat grown aboard the Russian space station Mir, space missions of long duration, or future manned space stations to generate oxygen, purify water, remove carbon dioxide, produce food and recycle waste materials. (Supported by NASA Grant NCC 2-831 and the Utah Agr. Expt. Station.)

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Lori A. Black, Terril A. Nell, and James E. Barrett

Dormant-budded `Gloria' azaleas (Rhododendron sp.) were used to observe the effect of forcing irradiance, temperature, and fertilization on postproduction performance after flower bud dormancy had been broken. Four experiments were conducted during forcing, the treatments for each experiment were: Expt. 1, three forcing irradiances (200,460, and 900 μmol·m-2·s-1) and three postproduction irradiances (4, 8, and 16 μmol·m-z·s-1); Expt. 2, three forcing irradiances (320, 560, and 1110 μmol·m-2s-l); Expt. 3, three controlled day/night temperatures (18/16C, 23/21C, and 29/27C); Expt. 4, fertilizer applied for 7, 14, or 28 days at either 150 or 300 mg N/liter (12% nitrate, 8% ammoniacal) 20N-4.8P-16K soluble fertilizer at every watering, control plants did not receive fertilizer. Days to harvest (time until plants had eight individual open flowers) was less at the high forcing irradiances and temperatures and when fertilizer was applied during forcing. Flower color was less intense at the low forcing irradiance levels, high temperatures, and when duration of fertilization was prolonged and concentration was high. There were more open flower inflorescences at week 2 of postproduction at high forcing irradiance levels, but their number was not affected by forcing temperature or fertilization. Postproduction longevity was shorter when forcing was at 29/27C (day/night) and when plants were fertilized for 28 days at 300 mg N/liter, but was not affected by forcing or postproduction irradiance.

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Douglas A. Bailey and William B. Miller

Plants of Euphorbia pulcherrima Wind. `Glory' were grown under total irradiances of 13.4, 8.5, or 4.0 mol·m-2·day-1 and sprayed with water (control), 2500 mg daminozide/liter + 1500 mg chlormequat chloride/liter (D + C), 62.5 mg paclobutrazol/liter, or 4, 8, 12, or 16 mg uniconazole/liter to ascertain plant developmental and postproduction responses to treatment combinations. Anthesis was delayed for plants grown under the lowest irradiance. Anthesis was delayed by the D + C treatment, whereas other growth retardant treatments had no effect on anthesis date. Irradiance did not affect plant height at anthesis, but all growth retardant treatments decreased height over control plants. Inflorescence and bract canopy diameters were decreased at the lowest irradiance level. Growth retardants did not affect individual inflorescence diameters, but all, except paclobutrazol and 4 and 8 mg uniconazole/liter, reduced bract canopy diameter compared with control plants. Plants grown under the lowest irradiance developed fewer inflorescences per plant and fewer cyathia per inflorescence. Cyathia abscission during a 30-day postanthesis evaluation increased as irradiance was decreased; cyathia abscission was unaffected by growth retardant treatment. Leaf abscission after 30 days postanthesis was lowest for plants grown under the lowest irradiance. At 30 days postanthesis, all growth retardant treatments increased leaf abscission over controls. Results indicate that irradiance and growth retardant treatments during production can affect poinsettia crop timing, plant quality at maturity, and subsequent postproduction performance. Chemical names used: 2-chloroethyl-N,N,N-trimethylammonium chloride (chlormequat chloride); butanedioic acid mono (2,2-dimethyl hydrazide) (daminozide); β-[(4-chlorophenyl) methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol), (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-l-penten-3-ol (uniconazole, XE-1019).

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Raymond Kessler, Allan M. Armitage, and David S. Koranski

Plug flats of Begonia × semperflorens-cultorum Hort. `Pizzazz Red', Vodka', and `Viva' were provided 0, 50, 125, or 200 μmol·s-1·m-2 metal-halide supplemental irradiance in the greenhouse for 0, 2, 4, 6, or 8 weeks. Treatments were initiated when seedlings were in the first true leaf stage (2 weeks after sowing). Plug-grown begonias reached transplantable dry weight and leaf area after 4 weeks of 125 μmol·s-1·m-2 supplemental exposure, while those under O and 50 μmol·s-1·m-2 required 6 to 8 weeks. Fewest number of days to visible bud and anthesis and the fewest number of nodes for all cultivars occurred after 2 weeks of 125 μmol·s-1·m-2 supplemental exposure. The same conditions achieved the greatest final leaf area and plant height; however, final dry weight was unaffected. Additional supplemental irradiance and/or exposure time did not accelerate flowering or improve vegetative growth of finished plants.