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Amanda Miller and Allan M. Armitage

The influence of temperature, irradiance, photoperiod and growth retardants on growth and flowering of Angelonia angustifolia Angel Mist series was evaluated. When temperature was increased from 15 to 30 °C, time to visible bud and time to flower decreased in a quadratic manner but total plant height and flower stem dry weight increased linearly. As irradiance increased, time to flower, time to visible bud, and height decreased quadratically. Changes in photoperiod had no effect on growth or flowering, suggesting that A. angustifolia is a day-neutral species with regards to height and flowering time. Daminozide, ancymidol, and paclobutrazol resulted in significant reduction of plant height compared with control plants but did not influence flowering time. Chemical names used: K-cyclopropyl-K-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); butanedioic acid mono (2,2-dimethylhydrazide) (daminozide); K-[(4-chlorophenyl)methyl]-K-(1,1-dimethyethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Trinidad Reyes, Terril A. Nell, James E. Barrett, and Charles A. Conover

The effect of irradiance and fertilizer level on the acclimatization of Chamaedorea elegans Mart. was studied. Chamaedorea elegans was grown for 4 months in 1.6-liter pots under 162, 306, or 564 μmol·m–2·s–1 and fertilized weekly with 20N–4.7P–16.6K soluble fertilizer at 220, 440, or 880 mg/pot. At the end of the production period, plants were moved to interior rooms and maintained for 2 months at 20 μmol·m–2·s–1 for 12 h daily at 21 ± 1C and a relative humidity of 50% ± 5%. At the end of the production phase, the light compensation point (LCP) and the concentration of nonstructural carbohydrates were lower, and chlorophyll concentration was higher the lower the irradiance level. Increasing fertilizer concentration decreased the number of fronds, LCP, and nonstructural carbohydrates. After 2 months in the interior environment, LCP and number of fronds of C. elegans did not differ among treatments. Chlorophyll concentration of plants grown under 564 μmol·m–2·s–1 had increased 61%, while starch in the stem had decreased 43% relative to the concentration found at the end of the production period. In C. elegans grown under 306 μmol·m–2·s–1, stem starch depletion was only 13% during the interior evaluation period. These results indicated that C. elegans grown under the highest irradiance level used reserved carbohydrates in the interior environment while adjusting to low light and producing new leaves. Chamaedorea elegans was best acclimatized at the intermediate irradiance and medium fertilizer concentration.

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John L. Jifon and Jim Syvertsen

Maximum CO2 assimilation rates (ACO2) in citrus are not realized in environments with high irradiance, high temperatures, and high leaf-to-air vapor pressure differences (D). We hypothesized that moderate shading would reduce leaf temperature and D, thereby increasing stomatal conductance (g s) and ACO2. A 61% reduction in irradiance under aluminum net shade screens reduced midday leaf temperatures by 8 °C and D by 62%. This effect was prominent on clear days when average midday air temperature and vapor pressure deficits exceeded 30 °C and 3 kPa. ACO2 and gs increased 42% and 104%, respectively, in response to shading. Although shaded leaves had higher gs, their transpiration rates were only 7% higher and not significantly different from sunlit leaves. Leaf water use efficiency (WUE) was significantly improved in shaded leaves (39%) compared to sunlit leaves due to the increase in ACO2. Early in the morning and late afternoon when irradiance and air temperatures were low, shading had no beneficial effect on ACO2 or other gas exchange characteristics. On cloudy days or when the maximum daytime temperature and atmospheric vapor pressure deficits were less than 30 °C and 2 kPa, respectively, shading had little effect on leaf gas exchange properties. The results are consistent with the hypothesis that the beneficial effect of radiation load reduction on ACO2 is related to improved stomatal conductance in response to lowered D.

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Douglas A. Hopper and Steven E. Woerner

Three-year-old Rosa hybrida L. `Royalty' and `Red Success' plants were pinched 20 Oct. and 22 Dec. 1990 to time production for Christmas and Valentine's Day, respectively. Two greenhouses received ambient solar radiation while two additional houses had 50% reduction in irradiance using a shading thermal blanket. All temperature set points were 23C/17C day/night. Every 10 days and at flowering shoots were measured for leaf (node) number, stem diameter, stem length, and fresh weights of stem, leaves, and flower bud. Time to visible bud and to flowering from pinch were recorded.

A computer model, ROSESIM, had been formulated in SLAM II and converted to both FORTRAN and BASIC code to make the program more portable. Although ROSESIM closely predicted `Royalty' fresh weights when irradiance was high before Christmas, underprediction occurred in the lower irradiance before Valentine's Day, and time to flowering was predicted earlier than was observed under all conditions. Corrective coefficients were added to ROSESIM to improve accuracy of prediction under actual greenhouse conditions.

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J.L. Catley

The influences of temperature and irradiance on flowering of two species of Leucocoryne [L. coquimbensis F. Phil and L. ixioides (Hook.) Lindl.] were examined in controlled environment growth rooms. Growing environments had day/night temperatures of 10/5, 15/10, or 20/15 °C, providing mean temperatures of 7.5, 12.5, or 17.5 °C, and photosynthetic photon fluxes (PPF) of 497 or 710 μmol·m-2·s-1. Inflorescence emergence data were recorded up to three times a week, measurements of floral development were made twice weekly and destructive harvests were carried out every 2 weeks. Both species of Leucocoryne flowered most quickly when grown at a mean temperature of 17.5 °C. Leucocoryne coquimbensis flowered first in all temperature regimes (means of 7.5, 12.5, or 17.5 °C), taking an average of 7.1, 5.1, or 4.5 months to flower, whereas plants of L. ixioides took 7.6, 5.4, or 4.7 months to flower. Although taking longer to flower, L. ixioides produced better quality flowers (taller scapes and more florets per inflorescence). Plants of L. coquimbensis grown in the two highest temperature regimes produced up to four inflorescences per bulb. As mean temperature decreased, the number of inflorescences produced by each bulb together with the number of florets in each inflorescence and the number of leaves produced before emergence of the inflorescence decreased. Decreases in these attributes were much greater with a 5 °C mean temperature drop from 12.5 °C, than a drop from 17.5 to 12.5 °C. At least half the florets in an inflorescence opened before the first floret began to senesce. The onset of senescence was delayed as mean temperature decreased. The highest irradiance level promoted development of further inflorescences of L. ixioides at all mean temperatures, and at a mean temperature of 17.5 °C for L. coquimbensis. Flower stem heights of L. coquimbensis increased as mean temperature increased and irradiance level decreased. An increase in irradiance level also promoted scape heights of L. ixioides, although maximum scape heights were attained at a mean temperature of 12.5 °C. Regardless of mean temperature or irradiance level, all cut stems were able to stand without support. These findings suggest days to flowering, inflorescence number and floral quality may be improved by growing these two species of Leucocoryne at mean temperatures greater than 17.5 °C, whereas mean temperatures below 12.5 °C will be detrimental to these floral attributes.

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S. Burrell, D. Mortley, P. Loretan, A.A Trotman, P. P David, and G. W. Carver

The effects of light intensity on three sweetpotato cultivars [Ipomoea batatas (L.) Lam] were evaluated in growth chambers, as part of NASA's Closed Ecological Life Support Systems (CELSS) program for long duration space missions. Vine cuttings of `TI-155', `GA Jet', and TUJ1 were grown using nutrient film technique (NFT) in a modified half Hoagland's solution with a 1:2.4 N:K ratio in channels (0.15×0.15×1.2 m). Plants were exposed to irradiance levels of 360 or 720 umols m-2s-1 with an 18/6 photoperiod in a randomized complete block design with two replications. Temperature was set at 28:22 lightdark and RH was 70%. Differences in plant response to were more related to cultivars than the effect of light intensity. Storage root number (8) fresh, (786 g/plant) and dry weights (139 g/plant) were highest for `TI-155' while foliage fresh and dry weights were highest for `TUJ1' when averaged across light levels. TI-155' (921 g/plant) and `GA Jet' (538 g/plant) produced greater yields at higher irradiance. `TUJ1' produced a higher yield (438 g/plant at the lower intensity compared to 219 (g/plant) at the higher intensity, suggesting this cultivar could produce storage roots in similar conditions in a CELSS.

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

A study was conducted to determine if photoperiod, irradiance, and/or a cool temperatures impacted flowering of selected species in five cactus genera. Gymnocalycium, Rebutia, Lobivia, and Sulcorebutia plants were grown for 4 months under natural daylight conditions (August–November) in a greenhouse maintained at 26 ± 2 °C. Plants were then placed in either of two greenhouses: 1) a greenhouse maintained at 22 °C day/18 ± 1 °C night temperature with an 8-h daylength (SD) or natural daylight plus night interruption lighting (NI; 2200–0200 HR), or 2) a greenhouse maintained at 5 ± 2 °C under natural daylight conditions (8–10 h). After 12 weeks at 5 °C, plants were moved to the SD and NI lighting treatments in the before mentioned greenhouse and additional lighting treatment [natural daylight plus supplemental high-pressure sodium lighting (85–95 μmol·m-2·s-1; 0800–0200 HR)]. In all cases, plants were moved out of lighting treatments after 6 weeks and were then grown under natural daylight conditions in a greenhouse maintained at constant 22 ± 1 °C. Data were collected on the approximate date growth commenced, the date when each flower opened (five flowers only), flower number per plant, and individual flower longevity (five flowers only). Species were classified into photoperiodic and irradiance response groups where appropriate and whether species exhibited a vernalization requirement was reported. Lastly, whether dormancy occurred and what conditions overcame that dormancy was reported.

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D.C. Ferree, S.J. McArtney, and D.M. Scurlock

Vines of container grown `DeChaunac', `Vidal blanc', `Seyval blanc' and `Chambourcin' grapes were subjected to 5 days of 80% shade at prebloom, bloom or 2 and 4 weeks after bloom. Fruit set, cluster weight, berries per cluster and juice components [soluble solids concentration (SSC), pH and titratable acidity] of `DeChaunac' and `Vidal blanc' were not affected by a short period of intensive shade. `Chambourcin' was sensitive to a shade period near the time of bloom for most of the aforementioned factors, while `Seyval blanc' was intermediate in sensitivity. Shot (green, hard, and undersized) berries of `Chambourcin' and `Seyval blanc' were increased by a 5-day period of shade 2 or 4 weeks after bloom. In a second study, container-grown `Chambourcin' on 3309C (V. riparia × V. rupestris) with one or two clusters and `Vidal blanc' with one cluster were subjected to the following light regimes beginning at bloom for 5 weeks: supplemental light, ambient greenhouse light and 30%, 50% or 80% shade. Yield, fruit set, specific leaf weight (leaf dry weight/leaf area), saturation index, and total leaf chlorophyll increased linearly with increasing irradiance. `Chambourcin' juice pH, SSC, leaf chlorophyll a/b ratio, cluster color development and hue angle decreased as irradiance increased, likely related to crop reduction. Responses in `Vidal blanc' followed similar trends, but differences were not as great. Results demonstrate that light is an important determining factor in fruit set of French-American hybrid grapes and fruit set of some cultivars are sensitive to short periods of intense shade.

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J.L. Catley

The influences of temperature and irradiance on vegetative growth of two species of Leucocoryne (Leucocoryne coquimbensis F. Phil and L. ixioides (Hook.) Lindl.) were examined in controlled environment growth rooms. The growing environments had day/night temperatures of 10/5, 15/10, or 20/15 °C, providing mean temperatures of 7.5, 12.5, or 17.5 °C, and photosynthetic photon fluxes (PPF) of 497 or 710 μmol·m-2·s-1. Leaf emergence data were recorded up to three times a week, and measurements of vegetative growth were made in the rooms twice weekly. Destructive harvests were carried out at intervals up to four weeks apart. Leaves of L. ixioides emerged first in all mean temperatures. As mean temperature decreased from 17.5 to 7.5 °C, the differences in first emergence dates became more apparent between species. Appearance of the second leaf of both species occurred in less than half the number of days the first leaf took to emerge. The time taken for further leaves to develop increased as temperature decreased, particularly for L. ixioides and at mean temperatures below 12.5 °C. Although leaves of L. ixioides emerged first, days to emergence of further leaves increased to lag behind production of L. coquimbensis leaves, particularly when mean temperatures dropped below 12.5 °C. Temperature also significantly affected growth of other plant parts. As mean temperature increased, maximum leaf, root and main bulb dry weights increased for both species, along with secondary bulb dry weights of L. coquimbensis. As irradiance increased, maximum leaf dry weights decreased and maximum bulb dry weights increased of both species, and maximum dropper dry weights of L. coquimbensis increased. Leucocoryne coquimbensis appears to have the greatest capacity to multiply vegetatively and this is enhanced by high mean temperatures. These results suggest that mean temperatures higher than those used in this study are required for sustained leaf emergence, particularly for L. ixioides although this species has the capacity to emerge at low temperatures. High mean temperatures are also likely to promote vegetative mass of all plant parts of both species, whereas higher irradiance levels than used in this study would enhance main bulb growth.

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Hiphil S. Clemente and Thomas E. Marler

Field-grown `Red Lady' papaya (Carica papaya L.) plants were used to measure foliar gas-exchange responses to rapid changes in irradiance levels to determine if papaya stomata are able to track simulated sun-to-cloud cover transitions. Natural sunlight and neutral shade cloth placed over the leaf were used to provide high photosynthetic photon flux (PPF) of about 2000 μmol·m-2·s-1 until leaves reached steady state within the cuvette, followed by three minutes with low PPF of about 325 μmol·m-2·s-1, and a return to PPF of about 2000 μmol·m-2·s-1. Net CO2 assimilation (A) declined from an initial 20 μmol·m-2·s-1 to about 9 μmol·m-2·s-1 within 20 seconds of initiating low PPF, and remained fairly stable for the duration of the three minutes of low PPF. Stomatal conductance (gs) declined within 60 seconds of initiating low PPF, from 385 to about 340 μmol·m-2·s-1 during the three minutes duration of low PPF. Following the return to high PPF, A rapidly increased to about 18 μmol·m-2·s-1, then gradually increased to the original value. After a lag of about 1 minute following the return to high PPF, gs began to increase and returned to the original value after three minutes. Container-grown `Tainung #1' papaya plants were used in a second study to determine the influence of mild drought stress on gas-exchange responses to rapid irradiance transitions. For drought-stressed plants, gs declined to a greater magnitude following the high-to-low PPF transition, and gs and A recovered more slowly following the transition from low-to-high PPF than for well-watered plants. Water use efficiency declined to a minimum immediately following the high-to-low PPF transition for both sets of plants, but recovered more rapidly for drought-stressed plants. These results indicate that papaya stomata are able to track rapid changes in irradiance, and mild drought stress enhances the tracking response.