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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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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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Christopher J. French and James Alsbury

Abstract

Night-break lighting using low irradiance incandescent lamps (INC) from 2000 to 0400 hr stimulated rooting of Rhododendron ‘Thomwilliams’ (R. thomsonii × R. williamsianum), R. ‘Pink Bountiful’ (R. williamsianum × ‘Linswegeanum’), and R. ‘Sonata’ (R. ‘Purple Splendour’ × R. dicroanthum) when applied during spring propagation (February to June). INC stimulated rooting of ‘Thomwilliams’ and ‘Sonata’, but had no effect on ‘Pink Bountiful’ in the fall (September to January). Supplementary irradiance during the day from high-pressure sodium lamps (HPS) had little effect on rooting in spring. In the fall, HPS stimulated rooting of ‘Pink Bountiful’ and ‘Sonata’, but had no effect on ‘Thomwilliams’. For all cultivars, INC was less effective in stimulating rooting when applied with HPS. A night break of 8 hr was more effective than one of 4 hr in stimulating rooting of ‘Thomwilliams’. INC stimulated initial rooting and did not increase root growth.

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D.J. Quatchak, J.W. White, and E.J. Holcomb

Abstract

The time between sowing and flowering (crop cycle) of geranium Pelargonium × hortorum Bailey was affected by light, temperature, chloromequat chloride (CCC), and cultivar. A minimum daily light integral of 17 mol·d−1·m−2, provided by high-pressure sodium lamps (HPS) prior to transplanting, accelerated flower initiation. HPS, low pressure sodium (LPS), and metal halide (MH) lamps, used as supplemental light after transplanting, reduced the crop cycle significantly compared to incandescent (INC) or natural light only. Crop cycles were similar among the HPS, LPS, and MH lamp treatments when equal-input lamp wattage was used per unit growing area, even though PPF values at the plant canopy varied. Plants grown at 21° and 27°C had a 5- to 15-day-shorter crop cycle than plants grown at 18° and 21°. Generally CCC reduced the crop cycle, but not consistently for all cultivar and lighting combinations. Chemical names used: 2-chloro-N,N,N-trimethylethanaminium chloride [chloromequat chloride (CCC)].

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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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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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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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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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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.