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James E. Faust and Royal D. Heins

Poor lateral branching sometimes occurs when certain poinsettia (Euphorbia pulcherrima) cultivars are pinched. Two experiments were conducted to determine the effect of high temperatures on axillary bud development. In Expt. 1, `Red Sails' plants were grown in a high-temperature environment (HTE) of 27°C at night (8 hr) and 30°C (3 hr), 33°C (10 hr), and 30°C (3 hr) in the day for two months, then transferred to a 20°C environment. In Expt. 2, plants grown at 20°C were transferred into the same HTE described above for 0, 2, 4, 8, 16, or 32 days and were then moved back into the 20°C environment. Axillary buds were examined for viability at the end of each experiment. In Expt. 1, only 8% of the lateral buds forming in the HTE were viable, while 80% of the buds forming in leaf axils of leaves unfolding after the plants were transferred to the 20°C environment were viable. In Expt. 2, 80% of buds produced in axils of the first four leaves to unfold after the start of the experiment were viable in all the treatments. However, the percentage of viable buds in the axils of leaf numbers 5 to 8 was 100, 100, 100, 96, 56, and 0 for the plants placed in the HTE for 0, 2, 4, 8, 16, and 32 days, respectively. These data indicate day temperatures of 30 to 33°C adversely affect lateral shoot development of `Red Sails' poinsettia.

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M.P. Kaczperski, W. H. Carlson, and M.G. Karlsson

Petunia × hybrids `Snow Cloud' plants were grown under 25 temperature combinations ranging from 10 to 30C and at photosynthetic photon flux levels of 100 or 200 μmol·s-1·m-2 (6.5 and 13 mol·day-1·m-2, respectively). Days to flower-was a quadratic function of average temperature, with 25C being the optimum temperature for minimal tire-e to flower at 200 μmol·s-1·m-2. Plant height increased “linearly and average internode length increased quadratically as day temperature increased. The number of lateral shoots decreased quadratically as average temperature increased, and the average length of each shoot decreased quadratically as day temperature increased.

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H.F. Wilkins, W.E. Healy, and K.L. Grueber

For chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura], the hypothesis that a 12-hr 5C or 13C dark treatment could be used in conjunction with a 12-hr 27, 21, 17, or 13C light treatment for rapid flowering when applied during certain developmental stages was valid. Flowering of `Bright Golden Anne', planted on 23 Sept., was not delayed by 12-hr light/12-hr dark growth chamber treatments of 21/5C or 27/13C (day/night) if treated from planting (P) of the rooted cutting to the start of short days (SD), 3 weeks after start of SD to visible bud (VB) (SD + 3 to VB), or from VB to flower (F) when compared to the glasshouse control plants grown at 21/18C. Plants responded similarly if grown at 13/13C or 21/21C, but flowering was delayed compared to the 17/17C glass house control. Delays were absent, however, when 13/13C was used from P to SD, SD + 3 to VB, or when 17/13 or 21/13C was used from VB to F.

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F. Todd Lasseigne, Stuart L. Warren, Frank A. Blazich, and Thomas G. Ranney

. splendens ‘St. John's Fire’ exposed to high temperatures (reaching a maximum of 45 °C) for 1 week. Fig. 1. Effects of day temperature on top dry weight of eight Salvia taxa. Symbols are means of 16 observations, vertical bars are ± 1 se , and

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Matthew G. Blanchard and Erik S. Runkle

and day temperatures between 24 and 27 °C ( Miller, 1992 ; Rohrl, 2005 ). Kubota et al., (2005) reported that plants grown at 18/8 °C or 23/13 °C (12-h day/12-h night) for 54 weeks had visible inflorescence (VI) percentages of 7% and 50

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Linsey A. Newton and Erik S. Runkle

for 3 to 7 weeks for a visible inflorescence (VI) to develop ( Krizek and Lawson, 1974 ; Sakanishi et al., 1980 ). The day temperature, not the night temperature, primarily controls inflorescence induction ( Blanchard and Runkle, 2006 ). Once plants

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Lívia Lopes Coelho, Amalia Fkiara, Kathryn Kuligowska Mackenzie, Renate Müller, and Henrik Lütken

/2000; Heraeus Vötsch GmbH, Balingen, Germany) with white LED lamps (FL300 SUNLIGHT fixture from Fiona Lighting; Senmatic A/S, Søndersø, Denmark), with an irradiance of ≈250 μmol·s −1 ·m −2 simulating the SD photoperiod (8 h day/16 h night) with a day

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Michael Alden and James E. Faust

bars represent ±1 SE. Table 1. Analysis of variance table demonstrating the significance of each main effect, including cultivar (Cvr), night length (NL), day temperature (DT), and night temperature (NT), and their interactions across all three

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Jens J. Brøndum and Royal D. Heins

Abbreviations: ADT, average daily temperature; DIF, day temperature - night temperature; DT, day temperature; DTF, days to flower; NT, night temperature; PPF, photosynthetic photon flux; SD, short day. 1 Current address: Danish Research Service for

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D. Bradley Rowe, Stuart L. Warren, Frank A. Blazich, and D. Mason Pharr

Catawba rhododendron (Rhododendron catawbiense Michx.) seedlings of two provenances, Johnston County, N.C. (35°45′N, 78°12′W, elevation = 67 m), and Yancey County, N.C. (35°45′N, 82°16′W, elevation = 1954 m), were grown in controlled-environment chambers for 18 weeks with days at 18, 22, 26, or 30C in factorial combination with nights at 14, 18, 22, or 26C. Seedlings of the higher-elevation provenance generally exhibited higher net leaf photosynthetic rates (PN)s than those from the lower elevation at all temperature combinations. Thus, it appears seedlings of the high-elevation provenance possess greater relative thermotolerance, expressed as net photosynthesis, than the low-elevation provenance. Eighty-seven days after initiation (DAI) of the experiment, PN showed a quadratic response to increasing day temperature, with the maximum occurring at 22C, whereas PN decreased linearly with increasing night temperature. At 122 DAI, PN increased linearly with increasing day temperature with nights at 22 and 26C. Highest PNs were at 30/22C and 26/22C. Carbohydrate export increased with increasing day temperature, whereas the response to night temperature was minimal. High levels of nonstructural carbohydrates occurred at thermoperiods (22/22C and 26/22C) that optimize seedling growth. However, definitive trends relating seedling growth to PNs, leaf carbohydrate levels, or to the amount of carbohydrate exported from the leaves were difficult to generalize due to numerous day × night interactions.