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ISHS Acta Horticulturae 515: XXV International Horticultural Congress, Part 5: Culture Techniques with Special Emphasis on Environmental Implications Chemical, Physical and Biological Means of Regulating Crop Growth in Ornamentals and Other Crops

FLORAL INITIATION IN EUPHORBIA PULCHERRIMA AT HIGH TEMPERATURES

Authors:   C.E. Wieland, J.E. Barrett, T.A. Nell, D.G. Clark
Keywords:   environment, Euphorbia pulcherrima, floriculture, flower initiation, flowering, photoperiod, poinsettia, temperature
Abstract:
Floral initiation and subsequent development was examined in six poinsettia cultivars (Euphorbia pulcherrima Wild.) under three photoperiod methods, natural days, black cloth, and lights out, to determine the differences amongst cultivars under different night lengths. Freedom Red, Bright Red Freedom, Pepride, and Ecke 702 had similar initiation, but Snowcap and Ecke 745 were an average of 3 and 7 days later, respectively than Freedom. There was a cultivar and photoperiod initiation for the number of days from initiation to first bract colour. Although cultivars had similar trends in initiation, they might show differences in the time to first colour. 702 was delayed in the time to first colour under natural days (18 days) and lights out (14 days) compared to the other cultivars (0–9 days). Freedom, Bright Red Freedom, and 745 were similar in the time to first colour under each photoperiod method, but black cloth reduced the time to first colour in Pepride, 702 and Snowcap. The number of days from initiation to visible bud was between 15 and 19 days for all cultivars under all photoperiods, with Freedom, Bright Red Freedom, and 745 developing a visible bud 3–4 days faster than Snowcap or 702. The number of days from initiation to anthesis was an average of 39–43 days for all cultivars. The time to anthesis for cultivars under natural days was 4 and 2 days longer, respectively than black cloth and lights out cultivars. Differences in cultivar flowering times were primarily due to floral initiation and time to first colour.
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