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Meriam Karlsson

The growth of Primula vulgaris Huds. `Dania Lemon Yellow' and `Blue Danova' was evaluated for plants grown at day/night temperature differences of 9, 3, 0, –3 or –9°C. The day temperature was maintained for the duration of the 16-hour photoperiod and the day and night temperatures were selected to provide an average daily temperature of 16°C. The plants were grown at the specific temperatures starting 8 weeks from seeding until flowering. Total daily irradiance was 12 mol·d–1·m–2. Time for visible flower bud, flower color and first open flower was recorded. Plant height and flower bud number were determined at the termination of the experiment. `Dania Lemon Yellow' plants grown with a positive or negative difference of 9°C were significantly (P < 0.05) later in reaching a visible bud stage. There were no differences however, in the number of days required for flower color or first open flower for `Dania Lemon Yellow'. Plants of `Blue Danova' showed a significant difference only in the number of days required for flowering. The plants grown with a positive or zero difference between day and night required on average 2 more days to reach the stage of first open flower. There were no significant differences in plant height or flower bud number in `Dania Lemon Yellow' or `Blue Danova'.

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Meriam Karlsson

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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Meriam Karlsson

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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Meriam Karlsson

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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Meriam Karlsson

Eight-week-old plants of Anemone coronaria L. `Mona Lisa Series' were transplanted into 10-cm pots and placed in growth chambers at 12, 16, or 20°C and 8, 12 or 16 hr of day length. The irradiance was 12 mol/day per m2. Following the exposure to treatment conditions for 8 weeks, the plants developed in a greenhouse at 16°C and 16 hr of 10-12 mol/day per m2. The fastest appearance of flower buds and flowering were observed for plants grown at 16 hr of day length and 16°C (77 ± 5.4 days from transplant, 133 days from seeding). However, the rate of development was not significantly different from the plants at 12°C and 12 hr of day length (81 ± 3.6 days). Flowering at 20°C required significantly more time at an average 93 ± 9.9 days from transplant. Leaf number at flowering increased with temperature from 9 1.5 leaves at 12°C to 12 ± 3.4 leaves at 16°C and 15 ± 3.4 leaves at 20°C. Flower stem length was significantly longer for plants grown at 12°C or 16 hr of day length (32 ± 0.5 cm) than plants grown at any of the other conditions (26 ± 0.5 cm). The average flower size (length of the petals) was 3.8 ± 0.6 cm for all plants in the study.

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Meriam Karlsson

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Meriam Karlsson* and Jeffrey Werner

The importance of far-red in the spectral energy distribution was evaluated for the development of Rudbeckia hirta. In a high pressure sodium production system of 8 mol·m-2 per day during 16 hours, a limited number of incandescent lamps were added to provide 15 to 20 μmol·m-2 s-1. The red to far-red ratio decreased through the addition of incandescent lighting from |2.2 of high pressure sodium to 1.2. The dwarf R. hirta cultivars Toto Gold, Toto Lemon and Toto Rustic, suitable as container or bedding plants, were transplanted into 10-cm containers 1 month after seeding and the experiment was initiated 3 weeks later. At this time, the plants had 7 to 8 leaves and were 3 to 4 cm in height. Flowering time decreased with 10 to 14 days for the R. hirta cultivars in the incandescent amended environment compared to exclusively high pressure sodium irradiance. Overall plant height averaged 24 cm for `Toto Lemon', 26 cm for `Toto Rustic' and 28 cm for `Toto Gold'. All three cultivars grew |4 cm taller by adding incandescent light. Main branches of each plant averaged 4 with 14 developed flowers and flower buds independent of cultivar and light quality. Average flower diameter increased 0.5 cm in incandescent amended environments to 7.1 cm for `Toto Gold' and `Rustic' and 6.4 cm for `Toto Lemon'.

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Meriam Karlsson and Jeffrey Werner

The rate of leaf unfolding for Cyclamen persicum Mill. was determined at 8 to 24 °C. Temperature treatments started 9 weeks from seeding and after 8 weeks all plants were moved to 16 °C. The cultivars Miracle Salmon, Miracle Scarlet, and Miracle White produced leaves at a similar rate. The relationship of (leaves/d) = - 0.01727 - 0.02284 * °C + 0.005238 * (°C)2 - 0.000162 * (°C)3 (R 2 = 0.99) best described the leaf unfolding rate in response to temperature. The maximum leaf unfolding rate was estimated to 0.329 leaves/day at 19.1 °C. Flower buds (2 mm diameter) developed within 60 days from the start of temperature treatments except at 8 °C. Thirty-five additional days at 16 °C were required for cyclamen initially grown at 8 °C for 8 weeks to produce flower buds. Despite similar conditions during bud development, flowering was delayed 14 to 18 days for plants initially grown at 24 °C compared to those grown at 12 to 20 °C. Plants initially at 8 °C did not flower within 70 days at 16 °C. Leaf and flower numbers at first open flower increased as initial temperature increased from 12 to 24 °C while dry weight and height only increased to 20 °C. No correlation between leaf unfolding and rate of flowering or flower number was detected. Recommendations for 20 °C during early cyclamen growth can be expected to support rapid rates of leaf unfolding and development, and large flower numbers.

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Meriam Karlsson and Jeffrey Werner

Cyclamen persicum (`Miracle Deep Salmon') was grown at 16 or 20 °C starting at transplant (70 d from seeding). Plants were maintained at the initial temperature of 16 or 20 °C for 3, 6, 9 weeks, or until flowering. Plant development was faster at 20 than 16 °C. Average time at 20 °C was 42 d to color appearance in the flower buds and 68 d to first open flower. At 16 °C, the average time was 58 d to flower bud color and 84 d for first open flower. Plants at 3 weeks of 16 °C flowered at a similar time as plants grown at 20 °C for 9 weeks or throughout. Three initial weeks at 20 °C resulted in similar time to flower as 16 °C throughout although flower color was recorded 9 d earlier for the plants initially at 20 °C. Time between flower bud color and open flowers averaged 26 d at both 16 and 20 °C. Significantly slower development from flower bud color to open flower was recorded with 3 or 6 initial weeks at 20 °C followed by 16 °C.