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R. Warner and J.E. Erwin

Hibiscus spp. seed were germinated and placed under different photoperiod treatments at 15, 20, or 25± 2°C. Photoperiod treatments were 9 hr, ambient daylight (≈9 hr) plus night interruption lighting (2200–0200 hr, 2 μmol·m–2·s–1 from incandescent lamps), or ambient daylight plus continuous light (100 μmol·m–2·s–1 light from high-pressure sodium lamps). Treatments were terminated at anthesis or after 20 weeks. Variation in flowering form and plant habit were documented and will be discussed. Temperature/photoperiod effects/interactions on plant development will be presented. Species were classified into appropriate photoperiodic groups. Those species with potential as new commercial floriculture crops will be presented.

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

Petunia × hybrida Vilm. cvs. `Purple Wave', `Celebrity Burgundy', `Fantasy Pink Morn', and `Dreams Red' were treated with temperature and photoperiod treatments for different lengths of time at different stages of development during the first 6 weeks after germination. Plants were grown with ambient light (≈8–9 hr) at 16°C before and after treatments. Flowering was earliest and leaf number below the first flower was lowest when plants were grown under daylight plus 100 μmol·m–2·s–1 continuous light (high-pressure sodium lamps). Flowering did not occur when plants were grown under short-day treatment (8-hr daylight). Plants grown with night interruption lighting from 2200–0200 HR (2 μmol·m–2·s–1 from incandescent lamps) flowered earlier, and with a reduced leaf number compared to plants grown with daylight + a 3-hr day extension from 1700–2000 HR (100 μmol·m–2·s–1 using high-pressure sodium lamps). Plant height and internode elongation were greatest and least in night interruption and continuous light treatments, respectively. `Fantasy Pink Morn' and `Purple Wave' were the earliest and latest cultivars to flower, respectively. Flowering was hastened as temperature increased from 12 to 20°C, but not as temperature was further increased from 20 to 24°C. Branching increased as temperature decreased from 24 to 12°C. Implications of data with respect to classification of petunia flower induction and pre-fi nishing seedlings are discussed.

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

Gomphrena globosa L. `Gnome Pink' and Salvia farinacea Benth. `Victoria Blue' were grown under different photoperiod treatments with day and night temperatures ranging from 15 to 30°C ± 1°C air temperature for 14 weeks after germination or until anthesis. Days to anthesis and leaf number were lowest when plants were grown under 9 hr of daylight and daylight plus 4-hr day extension from 1700–2100 HR (100 μmol·m–2·s–1 from high-pressure sodium lamps) for Gomphrena and Salvia, respectively. Days to anthesis decreased as temperature increased from 15 to 25°C with Gomphrena. Further increasing night temperature from 25 to 30°C delayed flowering and increased leaf number below the first flower of Gomphrena, but hastened flowering of Salvia. Plant height and internode elongation were greatest and least in the night interruption (2 μmol·m–2·s–1 from incandescent lamps from 2200–0200 HR) and continuous light (daylight plus 100 μmol·m–2·s–1 from high-pressure sodium lamps) treatments, respectively. Implications of these data with respect to classification of Gomphrena and Salvia flower induction are discussed and revised production schedules are presented.

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Jack W. Buxton and John N. Walker

Natural-light growth chambers constructed within a greenhouse compartment were equipped with a ventilation/circulation system, two stages of heating, and evaporative cooling. Air drawn from the greenhouse compartment continuously ventilated the chambers; the air was heated or cooled to the set-point temperature. A computer-controlled environmental system maintained uniform temperatures within the chambers and maintained the temperature within ±1C of the set point at night and during periods of low solar radiation; during higher solar radiation periods, control was not as precise. Carbon dioxide concentration was accurately maintained, and the photosynthetic photon flux from supplemental high-pressure sodium lamps was ≈200 μmol·m-2·s-1. The natural-light growth chambers provide a means for studying the interactive effects of temperature, light, and other environmental variables in experiments to increase production efficiency.

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G. Nordwig and J.E. Erwin

Asclepias sp. seed were germinated and placed under different photoperiod treatments at constant 15, 20, or 25 ± 2°C. Photoperiod treatments were 8 hr, 8 hr plus night interruption lighting (2200–0200 hr, 2 μmol·m–2·s–1 from incandescent lamps), day extension lighting 1700–2000 HR (100 μmol·m–2·s–1 from highpressure sodium lamps), or daylight plus continuous light (100 μmol·m–2·s–1 light from high-pressure sodium lamps) treatments. Treatments were terminated at anthesis or after 15 weeks. Variation in plant habit and flowering were documented. Also, temperature/photoperiod effects/interactions on plant development are discussed. Lastly, species were classified into appropriate photoperiodic groups and evaluated for potential use as new floriculture crops.

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A. Cutlan, J.E. Erwin, H. Huntington, and J. Huntington

Lamium maculatum L. `White Nancy', Scaevola aemula R. `New Blue Wonder', Verbena × hybrida Groenl. & Ruempl. `Tapian Blue', and Calibracoa × hybrida `Cherry Pink' were placed under different photoperiod treatments at constant 15, 20, 25, or 30 ± 2°C air temperature. Photoperiod treatments were 9 hr, ambient daylight (≈8 hr) plus night interruption lighting (2200–0200 hr, 2 μmol·m–2·s–1 from incandescent lamps), or ambient daylight plus continuous light (100 μmol·m–2·s–1 light from high-pressure sodium lamps). Data on plant development and rootability of cuttings from each environment was collected. Days to anthesis was lowest when plants were grown under the continuous lighting treatment across species. Verbena and Calibracoa stem elongation was greatest when grown under 30°C under continuous lighting. Species were classified as to photoperiodic flower induction groups. Implications of these data with respect to propagating and finishing these crops are discussed.

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Linda Gaudreau, Josée Charbonneau, Louis-P. Vézina, and André Gosselin

Two cultivars (Karlo and Rosanna) of greenhouse lettuce were grown under different photosynthetic photon fluxes (PPF) and photoperiods provided by 400-W high–pressure sodium lamps. Natural light was compared to suppletmental lighting treatments providing either 50 or 100 μmol m-2-s-1 for photoperiods of 16, 20 or 24 h. Lettuce plants were grown in hydroponic gulleys using a standard nutrient solution. Plant fresh weights were measured every week for the duration of each culture grown between August 1989 and June 1990. The incidence of tipburn and the overall quality of the shoots were determined at the end of each crop. Leaf nitrate contents and nitrate reductase activity were measured for various lighting treatments. The highest fresh weight was obtained for the highest PPF and the longest photoperiod. However, these treatments were associated with a higher incidence of tipburn. Supplemental lighting reduced the leaf nitrate contents and affected the nitrate reductase activity.

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J. Frick and C.A. Mitchell

Due to its short time to flower (14-18 days) and rapid maturation cycle (50-55 days), dwarf rapid-cycling brassica (Brassica napus) is under consideration as a candidate oilseed crop for NASA's Controlled Ecological Life Support Systems program. Recent work has focused on defining a set of optimum environmental conditions which permit increased crop yield in terms of g·m-2d-1 of edible biomass. A wide range of environmental variables have been considered including lamp type, CO2 level, nutrient solution pH, and planting density. In addition, nitrogen nutrition regimes have been manipulated with respect to nitrogen concentration (2 to 30 mM), source (NH4 + and/or NO3 -), and time of stepwise changes in nitrogen level (day 14 to 28). The highest seed oil content (42% DW basis) has been found under limiting nitrogen levels (2 mM). However, the low nitrogen inhibits overall seed production potential. Different cultural techniques also have been compared, including solid-substrate, passive wicking hydroponics versus liquid culture systems. Trials are underway to assess crop growth and development under the “best set” scenario of environmental conditions. At present, the highest seed yield (10.6 g·m-2d-1) has been obtained using solid-substrate hydroponic systems under a combination of metal halide and high-pressure sodium lamps. Constant CO2 enrichment to 1000 μmol·mol-1 did not increase crop yield rate.

Research supported in part by NASA grant NAGW - 2329.

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Gregory D. Goins, Neil C. Yorio, and Lynn V. Lewis

Various electric lamp sources have been proposed for growing plants in controlled environments. Although it is desirable for any light source to provide as much photosynthetically active radiation (PAR) as possible, light spectral quality is critical in regard to plant development and morphology. Light-emitting diodes (LEDs) and microwave lamps are promising light sources that have appealing features for applications in controlled environments. Light-emitting diodes can illuminate a narrow spectrum of light, which corresponds with absorption regions of chlorophyll. The sulfur-microwave lamp uses microwave energy to excite sulfur and argon, which produces a bright, continuous broad-spectrum white light. Compared to conventional broad-spectrum sources, the microwave lamp has higher electrical efficiency, and produces limited ultraviolet and infrared radiation. Experiments were conducted with spinach to test the feasibility of using LEDs and microwave lamps for spinach production in controlled environments. Growth and development comparisons were made during 28-day growth cycles with spinach grown under LED (at various red wavelengths), microwave, cool-white fluorescent, or high-pressure sodium lamps. Plant harvests were conducted at 14, 21, and 28 days after planting. At each harvest under all broad-spectrum light sources, spinach leaf growth and photosynthetic responses were similar. Major differences were observed in terms of specific leaf area and weight between spinach plants grown under 700 and 725 nm LEDs as compared to plants grown under shorter red wavelengths.

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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.