Abstract
Two experiments were conducted to accelerate growth of umbrella pine [Sciadopitys verticillata (Thunb.) Siebe & Zucc.]. Seedlings were grown in controlled-environment chambers at 22°/18°C (71.6°/64.4°F), 26°/22°C (78.8°/71.6°F) and 30 °/26 °C (86.0 °/78.8 °F) under short day (SD) and long day (LD) photoperiods. By 28 weeks, LD seedlings at 22 °/18 °C (71.6°/64.4°F) and 26°/22°C (78.8°/71.6°F) exhibited slightly greater growth. At this time, all plants except 30 °/26°C (86.0°/78.8 °F) SD were chilled 8 weeks at 4°C (39.2 °F) and returned to their respective growth chambers. Chilling substantially increased growth. At 22°/18°C (71.6°/64.4°F) and 26°/22°C (78.8°/71.6°F), the LD photoperiod produced more growth than the SD treatment. In the second experiment, plants from the first study grown at 22 °/18 °C (71.6 °/64.4 °F) SD and LD and 26 °/22 °C (78.8°/71.6°F) LD were divided into 2 groups. One group was placed back in the growth chambers in which they had been maintained during the first experiment. Remaining plants were chilled 8 weeks at 4°C (39.2 °F) and returned to their respective chambers. Excluding leaf length, growth at 22 °/18 °C (71.6 °/64.4 °F) LD, coupled with chilling, produced the largest values for all growth parameters.
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