ISHS Acta Horticulturae 711: V International Symposium on Artificial Lighting in Horticulture
HIGH TEMPERATURE DELAY OF FLORAL INITIATION IN MODERN POINSETTIA CULTIVARS |
| Authors: | R.A. Schnelle, J.E. Barett, D.G. Clark |
| Keywords: | Euphorbia pulcherrima, flowering, photoperiod, heat delay |
| Abstract:
The relative sensitivity of floral initiation to high temperatures in 16 modern poinsettia cultivars was investigated in a 2-year study. Night interruption lighting was used to prevent early initiation during a 4-week vegetative growth period. Temperature treatments were applied for 4 weeks after the cessation of night interruption lighting and photoperiod treatments were maintained through the completion of the experiments. After temperature treatments ended, all plants were grown to maturity with moderate temperatures (26°±2°/21°±2°C day/night average). Two photoperiod treatments were used: natural days at 29°40'N latitude and 13-hour dark period. In conjunction, two day/night temperature regimes were imposed: 24°/21°C (low) and 28°/24°C (high). For most cultivars, the date of first bract color, visible bud and anthesis were significantly delayed in the high temperature treatment under natural days compared to the low temperature treatment. Delay in anthesis between the low and high temperature treatments ranged from 0 to 19 days; 0 days in the cultivars ‘Orion’ and ‘Early Freedom Red’, 6 days in ‘Freedom Red’, 14 days in ‘Prestige Red’ and 19 days in ‘Cortez Burgundy’. In an additional study, ‘Prestige Red’ and ‘Freedom Red’ were exposed to elevated temperatures for 7, 14, or 21 days after the onset of short-days, and compared to the low temperature control, flowering in ‘Prestige Red’ was delayed 3, 6, and 10 days, respectively. Flowering in ‘Freedom Red’ was delayed only 0, 2, and 4 days, respectively. | |
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