Short day and cold as causative factors in the anthesis-like development of strobili of western red cedar (Thuja plicata)

Abstract

Short-day (SD) and low temperature (5 °C) treatments were tested separately to ascertain their contribution to the anthesis-like development of gibberellin-induced staminate and ovulate strobili of western red cedar (Thuja plicata Donn.). Low temperature, when given only for 8 weeks under long day (LD) where the daily sequence of photoperiod was kept continuously at 16 h resulted in expansion of 90% and 77% of the staminate and ovulate strobili respectively compared to 96% and 79% respectively where cold was given only during 8 weeks of SD in the sequence LD → SD → LD. Conversely, 8 weeks of SD given at warm temperature (19 °C) in the sequence of LD → SD → LD resulted in expansion of 9% and 1% of the staminate and ovulate strobili respectively. Thus, strobili of western red cedar can be said to have a cold requirement for normal anthesis-like expansion. In only a very small percentage of the strobili can SD (at least 8 weeks of SD) substitute for low temperature, and the low temperature treatment is effective regardless of photoperiod.