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J.W. White, H. Chen, and D.J. Beattie

Aquilegia ×hybrida `Bluebird' and `Robin', grown as greenhouse pot plants, initiated flower buds before cold exposure (4.5C) under supplemental high-pressure sodium lamps in mid-December, 5.5 months from sowing. Low temperature was the primary environmental factor that affected floral development in `Bluebird'. As the length of the cold exposure increased, the time between appearance of visible buds, anthesis, and petal shattering decreased, as did inflorescence number and total flower number per plant. Gibberellic acid (GA3) at 100 or 200 mg·liter-1 accelerated the appearance of visible buds during forcing in treatments without cold exposure. Soil drench applications of GA3 2 weeks before cold treatment accelerated floral development more than GA3 applied after cold exposure. Inflorescence number and total flower number per plant were reduced by 4 or 8 weeks but not by 2 weeks of exposure to cold. The developmental rate of “Robin', i.e., appearance of visible buds and anthesis, was quicker in plants with 18 to 20 leaves than in those with 12 to 14 leaves.

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Michael D. Berg and Preston K. Andrews

An aeroponic growth chamber is a system for growing plants in air with water and nutrients supplied by intermittent mist. This type of plant growth system is especially useful for experiments where root accessibility is desired. Tomatoes (Lycopersicon esculentum L. `Bonnie Best') were used to test the performance of an aeroponic growth chamber. A nutrient solution mist was applied through spray nozzles suspended below roots of supported seedlings. Mist application was regulated by electric timers, so that mist was applied for 50 sec. every 5 min. during the 16-hr light period, which was supplemented with a high-pressure sodium lamp. Root and stem lengths, leaf number and leaf lengths were measured weekly. Plastochron index (PI) was used to measure rate of leaf initiation. PI increased linearly, indicating uniform initiation of leaf primordia and absence of environmental stresses. Stem and root lengths increased consistently throughout the growing period. Each plant was harvested, separated into leaves, shoots and roots, oven dried, and dry weights measured.

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Mark A. Rose, David J. Beattie, and John W. White

Two distinct patterns of whole-plant transpiration (WPT) were observed in `Moonlight' rose (Rosa hybrida L.) using an automated system that integrated a greenhouse climate computer, a heat-balance sap-flow gauge, an electronic lysimeter, and an infrared leaf temperature sensor. One pattern consisted of a steady rate of transpiration in a stable greenhouse environment. The second pattern consisted of large oscillations in transpiration unrelated to any monitored microclimate rhythms. These oscillations had a sine-wave pattern with periods of 50 to 90 minutes and ranged from 2 to 69 g·h-1 in natural light and 3 to 40 g·h-1 under high-pressure sodium lamps at night. Leaf-air temperature difference (T1 - Ta) also oscillated and was inversely related to transpiration rate. Oscillatory transpiration has not been reported in roses. Plant scientists need to recognize the complex and dynamic nature of plant responses such as the oscillatory pattern of WPT monitored in Rosa hybrida when selecting monitoring and control strategies.

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David L. Bubenheim

The role of spectral quality and CO2 concentration in environmental control of lignin synthesis in spring wheat is being studied by the NASA Controlled Ecological Life Support System Program (CELSS). Wheat cultivars were exposed to four different spectral environments provided by 1) metal halide lamps (MH), 2) high pressure sodium lamps (HPS), 3) low pressure sodium lamps (LPS; almost monochromatic, 589 nm), or 4) LPS plus low irradiance blue light (5 μmol m-2 s-1; LPS + Blue) at equal photosynthetic photon flux. Stem lignin content was suppressed 25% under the LPS compared with the MH and HPS; blue addition (LPS + Blue) resulted in 25% greater lignin content compared with the LPS alone and 8% suppression compared with MH and HPS. CO2 studies compared lignin content of wheat grown in the field, greenhouse at 350 μmol mol-1 CO2, and growth chambers at 350 and 700 μmol mol-1 CO2, Lignin content was greatest and equal in the field and growth chamber at 700 μmol mol-1 CO2. Lowest lignin content was measured in the growth chamber at 350 μmol mol-1 CO2; lignin content in the greenhouse was intermediate between that measured in the field and growth chamber at 350 μmol mol-1 CO2, Additional CO2 studies in controlled environments will be discussed.

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J.E. Erwin, R. Warner, T. Smith, and R. Wagner

Viola × wittrockiana Gams. cvs `Delta Pure Rose' and `Sorbet Yellow Frost' were grown under different photoperiod and temperature treatments (12–24 ± 2°C) for different lengths of time at different stages of development during the first 6 weeks after germination. Plants were grown with ambient light (≈9 hr) at 16°C before and after treatments. Days to anthesis and leaf number were lowest when plants were grown under night interruption from 2200–0200 hr (2 μmol·m–2·s–1 from incandescent lamps) and daylight plus continuous light (100 μmol·m–2·s–1 from high-pressure sodium lamps) for `Sorbet Yellow Frost' and `Delta Pure Rose', respectively. Days to anthesis decreased as temperature increased from 12 to 24°C. Plant height and internode elongation were greatest and least in the night interruption and continuous light treatments, respectively. Branching decreased as temperature increased from 12 to 24°C. Implications of these data with respect to classification of Viola × wittrockiana flower induction and development of prefinished seedlings is discussed.

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Hassan Chadjaa, Louis-Phillipe Vézina, Sylvain Dubé, and André Gosselin

Two cultivars of lamb's lettuce (Valerianella sp L. cvs. Valgros et Vit) and one cultivar of spinach (Spinacea oleracea L. cv. Martine RZ Fl) were subjected to supplemental lighting treatments provided by high-pressure sodium lamps (HPS, PL 90, P.L. Lighting Systems). The PAR level was 50 μmol m–2 · s–1. Seedlings were subjected to three photoperiods (natural, 12, and 16 h). The experiment was conducted from Jan. until Apr. 1994. The fresh weight of plants grown under supplemental light was higher than plants grown under natural light. Nitrate concentration was lower in the leaves of plants grown under supplemental light while nitrate reductase activity (NRA) was increased. The cultivar Valgros was more productive than Vit, but accumulated more nitrates. At harvest, the fresh weight of Valgros plants grown under 12- and 16-h photoperiods were 30% and 50% higher, respectively, than those grown under natural photoperiod. The fresh weight of Vit grown under 16 h of supplemental light was 30% higher than under natural photoperiod. The lowest nitrate concentrations in plants were obtained under a 16-h photoperiod and the highest NRA were obtained with the same treatment. Compared to that obtained under natural photoperiod, the fresh weight of spinach shoots was 40% higher when seedlings were lighted for 12 h and almost 100% under 16 h. The lowest nitrate accumulation in spinach was found for plants grown under 16 h supplemental lighting.

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Robert W. Langhans and Mauricio Salamanca

With the primary objective of assuring food safety at the production level, a HACCP (Hazard Analysis and Critical Control Point) plan was developed and implemented in an 8000-ft2 greenhouse producing 1000 heads of lettuce per day in Ithaca, N.Y. The plan was developed following the HACCP principles and application guidelines published by the National Advisory Committee on Microbiological Criteria for Foods (1997). The CEA glass greenhouse uses both artificial high-pressure sodium lamps and a shade curtain for light control. Temperature is controlled via evaporative cooling and water heating. Lettuce plants are grown in a hydroponic pond system and are harvested on day 35 from day of seeding. Known and reasonable risks from chemical, physical, and microbiological hazards were defined during the hazard analysis phase. Critical control points were identified in the maintenance of the pond water, the operation of evaporative coolers, shade curtains, and during harvesting and storage. Appropriate prerequisite programs were implemented before the HACCP plan as a baseline for achieving minimum working conditions. Proper critical limits for some potential hazards were established and monitoring programs set up to control them. Postharvest handling was setup in an adjacent head house that was adapted as a food manufacturing facility according to New York State Dept. of Agriculture and Markets standards. Potential applications will be discussed.

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Mark P. Kaczperski and Royal D. Heins

Plug-grown Pelargonium × hortorum `Pinto Red' seedlings were grown under natural daylight (average of 4.7 mol/day) or with supplemental irradiance from high-pressure sodium lamps. Seedlings were grown under 8-, 16-, or 24-h photoperiods with supplemental irradiances of 2.5, 3.75, or 5.0 mol/day at each photoperiod. Supplemental irradiance was provided for 7, 14, 21, and 28 days beginning 7, 14, 21, 28, and 35 days after sowing. Seedlings were transplanted 63 days after sowing to 8-cm containers (121 plants/m2) and grown to flower. Leaf number at time of transplant was not affected by photoperiod, but increased as daily irradiance and weeks of supplemental irradiance increased. Seedlings were more responsive to supplemental irradiance applications beginning 28 and 35 days than at 7 to 21 days after sowing. Ninety-two percent of seedlings receiving 28 days of 5.0 mol/day supplemental irradiance under a 24-h photoperiod starting 35 days after sowing had initiated flower buds at time of transplant; 75% of those receiving 3.75 mol/day were initiated. Plants receiving less than 3 weeks of supplemental irradiance or with an irradiance period beginning less than 28 days after sowing had not initiated flowers at transplant.

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Ryan M. Warner and John E. Erwin

Thirty-six Hibiscus L. species were grown for 20 weeks under three lighting treatments at 15, 20, or 25 ± 1.5 °C air temperature to identify flowering requirements for each species. In addition, species were subjectively evaluated to identify those species with potential ornamental significance based on flower characteristics and plant form. Lighting treatments were 9 hour ambient light (St. Paul, Minn., November to May, 45 °N), ambient light plus a night interruption using incandescent lamps (2 μmol·m-2·s-1; 2200 to 0200 hr), or ambient light plus 24-hour supplemental lighting from high-pressure sodium lamps (100 μmol·m-2·s-1). Five day-neutral, six obligate short-day, six facultative short-day, three obligate long-day, and one facultative long-day species were identified. Fifteen species did not flower. Temperature and lighting treatments interacted to affect leaf number below the first flower and/or flower diameter on some species. Hibiscus acetosella Welw. ex Hiern, H. cisplatinus St.-Hil., H. radiatus Cav., and H. trionum L. were selected as potential new commercially significant ornamental species.

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In the article “Comparison of Intracanopy Light-emitting Diode Towers and Overhead High-pressure Sodium Lamps for Supplemental Lighting of Greenhouse-grown Tomatoes” by Celina Gómez, Robert C. Morrow, C. Michael Bourget, Gioia D. Massa, and Cary A