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Three-month-old plants of Ranunculus asiaticus L. `Bloomingdale Mix' were transplanted into 10-cm pots and placed in growth chambers at 12, 16, or 20°C and 8, 12, or 16 hours day length. The irradiance was 12 mol·d–1·m–2. The fastest appearance of flower buds and flowering occurred for plants grown at 16 hours day length and 16°C or 12 hours day length and 20°C. At 16°C, plants grown at 8 hours photoperiod required 7–10 more days to reach the stage of visible flower bud than those plants grown at 12 or 16 hours day length. The number of days to flower from the initiation of experimental conditions varied from 53 ± 3.7 days (168 days from seeding) for plants at 16-hour days and 16°C or 12-hour days and 20°C to 74 ± 2.7 days (189 days from seeding) for plants at 8-hour days and 16°C or 12-hour days and 12°C. Largest number of buds and flowers (15 ± 2.2 flower buds) was observed on plants grown at 12 or 16°C and 12-hour photoperiod. Conditions with 8- or 16-hour days at 16°C or 12-hour days at 20°C resulted in a smaller number of buds and flowers (9 ± 3.2 flower buds).

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Petunia `Midnight Madness' plants were grown for 4 weeks starting 3 weeks after seeding, at 8 or 16 hours photoperiod and 3, 7.5, or 12 mol·d–1·m–2. The temperature was 20 ± 1°C throughout the study. The plants were allowed to flower following the 4 weeks photoperiod treatment at 16 hours of 6 mol·d–1·m–2. Petunias grown at long days flowered (first open flower) faster than those exposed to 8 hours day length for 4 weeks. Plants grown at short days required 8 to 10 more days for flowering compared to plants grown at the same irradiance delivered during a 16-hour day. Flowering was first observed 61 ± 0.9 days from seeding for the plants at long days and 12 mol·d–1·m–2. Plants grown at 8 hours and 3 mol·d–1·m–2 required on average 84 ± 0.8 days from seeding to reach flowering. The number of flowers and flower buds (10 ± 1.8 flower buds) was lower for plants grown at 12 mol·d–1·m–2 independent of day length. There were no significant differences in the number of flower buds (16 ± 2.6 flower buds) at termination of the experiment for the plants grown at the two lower irradiance levels for either 8 or 16 hours day length.

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Plants of four pansy cultivars (`Crystal Bowl Deep Blue', `Majestic Giant Blue', `Maxim Deep Blue' and `Universal True Blue') were grown for 4 weeks starting 24 days after seeding, at 8 or 16 hours photoperiod and 3, 7.5 or 12 mol·d–1·m–2. The temperature was 20 ± 1°C throughout the study. The plants were allowed to flower following the 4 weeks photoperiod treatment at 16 hours of 6 mol·d–1·m–2. The first open flower was observed significantly earlier for plants of `Majestic Giant', `Maxim' and `Universal' exposed to 16 hours at 12 mol·d–1·m–2 than any of the other day lengths and irradiance levels for 4 weeks. There was no difference in rate of flowering for plants of `Crystal Bowl' grown at 16 hours and 7.5 or 12 mol·d–1·m–2. At 3 mol·d–1·m–2, plant development was slowest and an 8 or 16 hours day length did not significantly affect rate of flowering for any of the four cultivars. Plants of `Crystal Bowl' had on average the fastest flowering (74 ± 2.2 days from seeding with 4 weeks at 16 hours of 12 mol·d–1·m–2) and plants of `Majestic Giant' the slowest flowering (83 ± 3.4 days from seeding to flower with 4 weeks at 16 hours of 12 mol·d–1·m–2) of the four cultivars.

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Dwarf Easter cactus [Rhipsalidopsis rosea (Lagerheim) Britton and Rose] plants were subjected to temperature and photoperiod treatments to determine their influence on flowering. All plants exposed to 10C at night (NT) and natural daylengths (ND) during winter and spring for 4 or more weeks flowered, whereas some plants grown continuously under 18C NT and either long days [(LD) provided by incandescent irradiation] or ND failed to flower. Days to flowering and number of flower buds per plant increased linearly as the duration of exposure to 10C NT and ND increased from 4 to 16 weeks. The number of flower buds were greatest on plants receiving either continuous 10C NT or 12 to 16 weeks 10C NT, then 18C NT until flowering. Plants receiving 18C NT flowered earlier under LD than ND when treatments followed 4 or 8 weeks-of 10C NT and ND.

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Photoperiodic response and vase life of 28 cultivars of ornamental sunflower (Helianthus annuus) were evaluated. Plants were grown in a glasshouse under 16-hour long-day (LD) or 11.5-hour shortday (SD) conditions. Most cultivars (82%) reached visible flower bud stage earlier under SD than LD. All cultivars flowered under both SD and LD conditions, but in 26 cultivars (92.9%) flowering was significantly delayed under LD, demonstrating them to be quantitative SD plants. The delay was variable among the cultivars. A 14-day or greater hastening of flowering was found under SD in 18 cultivars. Photoperiod had no effect on flowering of `Lemon Eclair' and `Moonshadow'; these cultivars are day-neutral (DN) plants. For some cultivars the LD photoperiod increased plant height and the number of nodes and leaves. Vase life varied from 6.8 to 11.2 days depending on the cultivar, but no photoperiodic effect was found.

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Abstract

Tomato seedlings (Lycopersicon esculentum Mill. ‘Heinz 1350’) were inoculated with the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatus (Thaxter) Gerd. & Trappe and either exposed to 30 pphm (589 μg/m3) ozone or to filtered air for 3 hours once weekly, beginning 3 weeks after inoculation, under long photoperiods (12–13.5 hr). Root infection by G. fasciculatus in ozone-exposed plants was retarded from week 3 to 5 compared to controls but recovered by week 7. Growth rates of mycorrhizal control plants were significantly greater than ozone-exposed mycorrhizal plants, but there were no differences in growth rates of nonmycorrhizal controls, mycorrhizal ozone-exposed plants, and nonmycorrhizal ozone-exposed plants. Under short photoperiods (less than 12 hr), growth rates of mycorrhizal controls were less than nonmycorrhizal controls and ozone did not significantly affect growth rates of nonmycorrhizal plants relative to controls. Leaf chlorophyll levels were similar whether plants were mycorrhizal, nonmycorrhizal, or exposed to ozone.

Open Access

Miltoniopsis orchids have appealing potted-plant characteristics, including large, fragrant, and showy pansylike flowers that range from white and yellow to shades of red and purple. Scheduling orchid hybrids to flower on specific dates requires knowledge of how light and temperature regulate the flowering process. We performed experiments to determine whether a 9- or 16-h photoperiod [short day (SD) or long day (LD)] before vernalization and vernalization temperatures of 8, 11, 14, 17, 20, or 23 °C under SD or LD regulate flowering of potted Miltoniopsis orchids. Flowering of Miltoniopsis Augres `Trinity' was promoted most when plants were exposed to SD and then vernalized at 11 or 14 °C. Additional experiments were performed to determine how durations of prevernalization SD and vernalization at 14 °C influenced flowering of Miltoniopsis Augres `Trinity' and Eastern Bay `Russian'. Plants were placed under SD or LD at 20 °C for 0, 4, 8, 12, or 16 weeks and then transferred to 14 °C under SD for 8 weeks. Another set of plants was placed under SD or LD at 20 °C for 8 weeks and then transferred to 14 °C with SD for 0, 3, 6, 9, or 12 weeks. After treatments, plants were grown in a common environment at 20 °C with LD. Flowering of Miltoniopsis Augres `Trinity' was most complete and uniform (≥90%) when plants were exposed to SD for 4 or 8 weeks before 8 weeks of vernalization at 14 °C. Flowering percentage of Miltoniopsis Eastern Bay `Russian' was ≥80 regardless of prevernalization photoperiod or duration. This information could be used by greenhouse growers and orchid hobbyists to more reliably induce flowering of potted Miltoniopsis orchids.

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Abstract

Dutch-grown tuberous-rooted dahlias, ‘Kolchelsee’ and ‘Park Princess’, were forced from January to June in 1975 and 1976. In all experiments, plant height was controlled by applying 0.5 mg/pot of ancymidol 2 weeks after planting.

Fertilization was essential and an application of one of several slow-release formulations of Osmocote or weekly applications of 20N—8.8P—16.6K (200 ppm N) as a soluble fertilizer produced high quality plants which flowered in approximately 70 days. The highest quality plants and best height control was obtained with 25°C day and 16° night temperatures. Flowering was delayed at 24/12° day/night temperatures, and although flowering was accelerated at 28/17° and 29/20° day/night temperatures plant quality was adversely affected.

Natural spring photoperiods which increased from 10 to 14 hours were optimal for forcing. Long days given either as a 16-hour photoperiod or as a 4-hour night break delayed flowering slightly. Dahlias grown under an 8-hour photoperiod flowered the earliest but not all plants flowered. Dahlias required high light intensities during forcing. Under 50% shading plants were too tall for pot plant use even after treatment with ancymidol.

Open Access

Abstract

Shoots harvested from the first and 2nd reculture of azalea (Rhododendron sp.) accession 800374 shoot tip cultures grown under 16 hr photoperiod from cool-white fluorescent light were taller and achieved higher quality ratings than shoots from 24 hr daily photoperiod. The number of shoots produced during the first reculture was the same for both 16 and 24 hr photoperiod, whereas significantly more shoots were harvested from cultures grown under 16 hr in the 2nd reculture. Similarly, 24 hr light inhibited elongation of shoots and decreased quality rating from in vitro-derived shoot cultures without any effect on the number of shoots per culture. Photosynthetic photon flux density (PPFD) of 30 and 75 μmol s−1m−2 (400–700 nm) increased number, length, and quality rating of shoots harvested from in vitro-derived shoot explants when compared to a 10 μmol s−1m−2 PPFD. However, recultured in vitro-derived shoot explants produced similar number and length of shoots under 10, 30, and 75 μmol s-1m-2, whereas the quality rating was reduced in cultures under 75 μmol s−1m−2. The highest percentage of rooting occurred in microcuttings harvested from cultures grown under 10 and the lowest under 75 μmol s−1m−2. Increasing the PPFD from 10 to 75 μmol s−1m−2 reduced shoot length and quality rating of rooted microcuttings, as well as root length and quality rating.

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Abstract

When Alstroemeria ‘Regina’ shoots were grown in a continuous 13°C air temperature, and the underground structures (rhizomes and roots) were placed in a 5°, 10°, 15°, 20°, or 25° water bath, plants produced 22%, 33%, 13%, 14%, or 5% generative shoots, respectively (Expt. 1). When the underground structures were grown at 13°, there were no differences in percentages of generative shoots, regardless if shoots were in a 13° or 21° air temperature, and regardless if shoots were under short or long photoperiods. When soil temperature was 21° and air temperature was 13°, 12% generative shoots were produced only with a night interruption photoperiod (Expt. 2). Data from these 2 experiments led us to conclude that floral induction was controlled primarily by temperatures to which the underground structures were subjected, regardless of the air temperature or photoperiod. Storage root and rhizome dry weights were promoted by 13° air, 13° soil temperatures and night interruptions with incandescent light. Treatments which had a high percentage of generative shoots also had high root and rhizome dry weights.

Open Access