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  • Author or Editor: John Erwin x
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The interaction among temperature, photoperiod, and irradiance on survival of Chamaecereus silvestrii (yellow sport) flat-grafted onto Hylocereus trigonus Haw. rootstock was studied in an effort to understand the basis for elevated scion necrosis during winter. Plants were placed in glasshouses maintained at 12, 16, 20, or 24 °C under either daylight (moles per day), 66% daylight or daylight + 100 μmol·s−1·m−2 irradiance levels. Plants were grown with an 8-hour (short day) or 8-hour + 4-hour night interruption (long day) photoperiod. Cactus scion necrosis increased under short days and a growing temperature of 12 °C and was nearly eliminated by long-day conditions and a growing temperature of 16 °C. Irradiance did not affect scion necrosis. Plant quality rating was highest when plants were grown under long-day conditions at 16 °C.

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Seedling stem elongation increased as the difference (DIF) between day (DT) and night (NT) temperatures increased from 10 to 26C (DIF=DT-NT). Stem elongation was primarily dependent on DIF on all crops studied except spring bulb crops. Internode lengths decreased in tomato (68%), watermelon (80%), squash (32%), sweet corn (68%) and snap bean (26%) as the difference between day and night temperatures decreased 12 degrees (C). Cucumber internode length decreased by 84% as DIF decreased 16 degrees (C). The ratio of male to female cucumber flowers decreased from 14 to 1, as DIF decreased 12 degrees (C) from 23 DT/17 NT to 17 DT/26 NT. Stem elongation was very sensitive to cool temperatures during the first 3 hours of the morning. Stem elongation was almost the same if the seedlings were cooled for the first 3 hours of the day versus cooling the plants all day. The interactions between temperature on stem elongation and light quantity and quality, and photoperiod will be discussed. Application of DIF in both northern and southern greenhouses will also be discussed.

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Green roofs are building surface treatments where plants are grown in medium on a rooftop to cool or insulate buildings and/or to ameliorate negative environmental impacts of buildings. We initiated a 2-year study to characterize medium and weather conditions on a rooftop in a cool-dry climate and to identify plant species with horticultural and ecological attributes that survive and thrive on an unirrigated semi-intensive green roof in a cool-dry climate. Eighty-eight cold-hardy, drought-tolerant species with horticultural or ecological attributes were identified and planted into 12.7-cm-deep medium in trays that were placed on a rooftop. Medium temperatures and moistures were recorded, and plant survival and vigor were quantified. Hourly medium temperatures varied from –22.3 to 43 °C. Monthly medium water moistures varied from –2.5 to –73.3 kPa from May to September, and from –7.6 to –195 kPa from October to April. Monthly air temperature, relative humidity and irradiance varied from –9.4 to 21.7 °C, 44% to 80%, and from 206 to 1222 μmol·m−2·s−1. Mean survival scores decreased (4 = 100% survival) from 2.6 with grasses, to 2.3 with succulents, to 1.8 with temperate perennials, to 0 for geophytes (all died). Among grasses, Festuca ovina VNS, Koeleria macrantha 07-901 ND, Panicum virgatum, and Sporobolus heterolepis performed well. Among succulents, Sedum acre, S. album ‘Coral Carpet’, S. cauticola ‘Sunset Cloud’, S. ‘Czar’s Gold’, S. ellecombianum, S. hybridum ‘Immergruchen’, S. requieni, S. sexangulare, S. spurium ‘Dragon’s Blood’, ‘John Creech’, ‘Pearly Pink’, ‘Ruby Mantle’, and ‘Tricolor’ performed well. Among temperature nonsucculent perennials, Allium ceranum and senescens ‘Glaucum’, Geum triflorum, Talinum calycinum, and Thymus praecox ‘Red Creeping’ performed well. Data on Sedum suggested that medium-low temperature was more limiting to survival than moisture level. The differences in species that performed well here, compared with other studies, underscores the importance of regionally specific green roof plant species studies.

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The impact of irradiance (0–1200 μmol·m−2·s−1) and carbon dioxide concentration (CO2; 50–1200 ppm) on kale (Brassica oleracea and B. napus pabularia; three cultivars), Swiss chard (chard, Beta vulgaris; four cultivars), and spinach (Spinacea oleracea; three cultivars) photosynthetic rate (P n; per area basis) was determined to facilitate maximizing yield in controlled environment production. Spinach, chard, and kale maximum P n were 23.8, 20.3, and 18.2 μmol CO2·m−2·s−1 fixed, respectively, across varieties (400 ppm CO2). Spinach and kale had the highest and lowest light compensation points [LCPs (73 and 13 μmol·m−2·s−1, respectively)] across varieties. The light saturation points (LSPs) for chard and kale were similar at 884–978 μmol·m−2·s−1, but for spinach, the LSP was higher at 1238 μmol·m−2·s−1. Dark respiration was lowest on kale and highest on spinach (−0.83 and −5.00 μmol CO2·m−2·s−1, respectively). The spinach CO2 compensation point (CCP) was lower (56 ppm) than the chard or kale CCP (64–65 ppm). Among varieties, ‘Red Russian’ kale P n saturated at the lowest CO2 concentration (858 ppm), and ‘Bright Lights’ chard saturated at the highest (1266 ppm; 300 μmol·m−2·s−1). Spinach P n was more responsive to increasing irradiance than to CO2. Kale P n was more responsive to increasing CO2 than to irradiance, and chard P n was equally responsive to increasing CO2 or irradiance. Implications and limitations of this work when “upscaling” to whole-plant responses are discussed.

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Interaction between simulated shipping and rooting temperature and harvest year was studied on Lilium longiflorum. Bulb dormancy and maturity appear to be separate phenomenon and are affected by temperature differently. Shoot emergence (an indicator of release from dormancy) was hastened by 10 °C shipping and 10 to 20 °C rooting temperatures in both years. Flower induction was affected differently by simulated shipping and rooting temperatures during 1992 and 1993, indicating that bulb maturity differed between the 2 years. Final leaf and flower number decreased because of shipping or rooting temperature, but only when bulbs were mature and received cool temperatures (<16 °C) before a 6-week vernalization treatment. Immature bulbs (at harvest) are unresponsive to vernalizing shipping and rooting temperatures. Prevernalization handling temperature and vernalization treatment length should vary with year based on degree of bulb maturity to achieve consistency in final morphology. Internode length is associated more with the time elongation is suppressed after dormancy is broken than with flower induction (where internode length increases as the length of time elongation is suppressed after breaking of dormancy increases).

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Wind, touching, and/or mechanical stress can restrict stem elongation. Removal of the registration of the growth retardant daminozide for use on edible crops increased interest in thigmotropic inhibition of stem elongation to control plant height in greenhouse crops, as well as a general desire by growers to decrease chemical inputs for floriculture crops. Since stem elongation varies diurnally, the question arises as to whether wind inhibition of stem elongation varies over a 24-hour period. Tomato (Lycopersicon esculentum) `MoneyMaker' and cosmos (Cosmos bipinnatus) `Imperial Pink' seedlings were placed under each of 10 wind perturbation treatments [applied for different durations and at different times during a 24-hour period; wind speed (perpendicular to the media) at seedling level was 30 km·h–1 (18.6 mph)] for 30 days. Data were collected on plant height and leaf number on days 1 and 30. The effect of wind on stem elongation differed with species; wind treatments restricted stem elongation more on cosmos than tomato (53% and 20%, respectively, across treatments). Tomato elongation was most restricted when seedlings received wind all day, all night, or all day and night. Within short-term treatments, internode length was least when tomato seedlings received a mid-day wind treatment. Cosmos elongation was most restricted when seedlings received a wind treatment all day or all night. Within short-term treatments, cosmos internode elongation was most restricted with early- and mid-day wind treatments. Data here suggest wind effects on elongation vary diurnally. In addition, the magnitude of wind effects on elongation varied with species and was greatest during the beginning of the day on cosmos, which mirrors when stem elongation is most sensitive to temperature fluctuations.

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One-time spray applications [about 6 mL (0.2 fl oz)] of chlormequat chloride [1000 or 2000 mg·L-1 (ppm)], daminozide (2500 or 5000 mg·L-1), paclobutrazol (20 or 40 mg·L-1) and uniconazole (5 or 10 mg·L-1) varied in efficacy in reducing Hibiscus coccineus (Medic.) Walt., H. radiatus Cav., and H. trionum L. (flower-of-an-hour) stem elongation. Chlormequat chloride inhibited stem elongation of all species, with a 2000 mg·L-1 application reducing stem length of H. coccineus, H. radiatus, and H. trionum by 87%, 42%, and 52%, respectively, compared to untreated plants, 28 d after application. Paclobutrazol also inhibited stem elongation of all species. Uniconazole reduced stem elongation of H. coccineus and H. radiatus, but not H. trionum. Daminozide applied at 5000 mg·L-1 reduced H. radiatus stem elongation only. Growth retardants examined in this study did not delay flowering of H. trionum, the only species that flowered during the experiment. (Chemical names used: ancymidol (α-cyclopropyl-α-(4-methoxyphenol)-5-pyrimidinemethonol), chlormequat chloride(2-chloroethyltrimethylammonium chloride), paclobutrazol ((+)-(R*,R*)-beta((4-chlorophenyl)methyl)-alpha-(1,1-dimethyl)-1H-1,2,4-triazol-1-ethanol), daminozide ([butanedioic acid mono(2,2-dimethylhydrazide)], uniconazol-P ((E)-(+)-(s)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pent-1-ene-3-ol)).

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Our objective in this study was to identify the effects of the photosynthetic daily light integral (DLI) on growth and flowering of six kalanchoe (Kalanchoe) species: Kalanchoe glaucescens, christmas tree plant (K. laciniata), chandelier plant (K. manginii), shovel leaf kalanchoe (K. nyikae), common kalanchoe or nentabos (K. rotundifolia), and velvet leaf kalanchoe (K. velutina). Plants were grown under an 8-hour photoperiod with a DLI of 4.3, 8.6, or 17.2 mol·m−2·d−1. Node numbers below the terminal inflorescence on K. glaucescens, K. manginii, K. nyikae, and K. rotundifolia decreased as the DLI increased, whereas node numbers of K. laciniata and K. velutina were unaffected by DLI. Time to first open flower of K. glaucescens, K. nyikae, and K. rotundifolia was unaffected by the DLI, whereas increasing the DLI from 4.3 to 17.2 mol·m−2·d−1 reduced the time to first open flower of K. laciniata, K. manginii, and K. velutina. Total flowers for all species increased as the DLI exceeded 4.3 mol·m−2·d−1. Shoot heights of K. glaucescens and K. rotundifolia increased as the DLI increased from 4.3 to 8.6 mol·m−2·d−1, whereas shoot height of K. nyikae decreased as the DLI increased from 4.3 to 17.2 mol·m−2·d−1; shoot heights of K. laciniata, K. manginii and K. velutina were unaffected by DLI. Dry weight gain increased for all species as the DLI exceeded 4.3 mol·m−2·d−1.

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One cactus and 17 succulent species/cultivars were grown at 10, 16, 22, or 28 °C (plant temperature) for 10 or 15 weeks. The change in leaf/tubercle number at each temperature (after 10 or 15 weeks) was determined, and leaf/tubercle-unfolding rate was calculated. ‘Jade Necklace’ kebab bush (Crassula rupestris ssp. marnieriana), ‘Lola’ echeveria (Echeveria), ‘Green Ice’ gasteraloe (Gasteraloe), and lithops (Lithops species) leaf-unfolding rate per day was unaffected by temperature. Leaf-unfolding rate per day increased as temperature increased from 10 to 16 °C on ‘Firebird’ aloe (Aloe), ‘Key Lime Pie’ adromischus (Adromischus cristatus), prostate rainbow bush (Portulacaria afra variegata), burro’s tail (Sedum burrito), and ‘Sir William Lawrence’ houseleek (Sempervivum calcareum). Leaf-unfolding rate per day increased as temperature increased from 10 to 22 °C on mescal agave (Agave parryi truncata), ‘Firebird’ aloe, Sunrise anacampseros (Anacampseros telephiastrum variegata), ponytail palm (Beaucarnea recurvata), subsessilis echeveria (Echeveria subsessilis), zebra plant (Haworthia fasciata), prostrate rainbow bush, burro’s tail and ‘Sir William Lawrence’ houseleek. Increasing temperature from 22 to 28 °C decreased ‘Kiwi’ tree houseleek (Aeonium percarneum) leaf-unfolding rate per day, increased ‘Firebird’ aloe and tiger tooth aloe (Aloe juvenna) leaf-unfolding rate, and resulted in shoot tip death on burro’s tail, and plant death of ‘Sir William Lawrence’ houseleek and ‘Silver Dollar’ jade (Crassula arborescens). The cactus, ‘Arizona Snowcap’ mammillaria (Mammillaria gracilis fragilis), tubercle-unfolding rate per day increased as temperature increased from 16 to 28 °C. Taken together, temperature (10 to 28 °C) effects on development rate were species specific and related to the indigenous environment of a species.

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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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