Loss and induction of conditional dormancy in seeds of Sitka spruce maintained moist at different temperatures

Pretreatment of moist seeds at certain temperatures can reduce seed dormancy, but such observations represent the net effect of pretreatment. Seeds of Sitka spruce (Picea sitchensis [Bong.] Carr.) were raised to 30% moisture content and pretreated at five different temperatures between 5 and 30 degrees C for up to 24 weeks (168 d). Subsequent ability to germinate at 10 degrees C and viability were then determined in order to investigate the effects of pretreatment on seed dormancy and survival. There was a curvilinear, negative semi-logarithmic relationship between seed longevity and pretreatment temperature, such that Q(10) for loss in viability increased from 2.6 between 10 and 20 degrees C to 2.8 between 20 and 30 degrees C. Simple multiplicative models combining cumulative normal frequency distributions for each of loss in viability and loss in dormancy were able to describe the changes in ability to germinate at 10 degrees C, after pretreatment at 5, 10 and 30 degrees C. However, in order to quantify the changes in ability to germinate observed at 10 degrees C after pretreatment at 15 degrees C, it was necessary also to invoke a model of dormancy reimposition, while for the results at 20 degrees C it was necessary to postulate both dormancy reimposition and the further loss of this reimposed dormancy. It is concluded that moist seeds of Sitka spruce held at 15 and 20 degrees C cycle between the dormant and non-dormant condition.