Douglas fir, Pseudotsuga menziesii (Mirb.) Franco, seeds exhibit relative dormancy as they do not germinate at suboptimal temperature (15°C), whereas at optimal temperature (20°C) some germination occurred. Thus, germination at 15°C was chosen to estimate dormancy release. In the first experiment, seeds were prechilled at 32% moisture content (MC) for 0-34 weeks at 3°C. Long chilling treatments enhanced germinability and, more markedly, germination speed both at 20°C and at 15°C. Seeds pretreated for the longest periods were then dried to 6.7% MC and stored up to 6 months without any detrimental effect on germination at 15°C. In the second experiment, seeds from a second seedlot were prechilled for 18 weeks and then stored at three different MCs over a period of 17 months. Seeds stored at the lowest MC (6.7%) germinated fastest and to the highest percentage both at 15 and 20°C. In the nursery, seedling emergence tests confirmed results from this experiment. In most cases, comparisons between seeds prechilled at controlled MC before storage and those stratified with the traditional method resulted in better performance of the first ones, both in the laboratory and in the nursery.
Beechnuts from two seedlots were pretreated, without medium, at a controlled moisture content (MC) of 30% before or after 1-year storage at 7 °C. Seeds treated with the two methods were germinated on substrates at decreasing osmotic potential down to 1.2 MPa. A moderate stress of 0.2 MPa caused a slight but significant decrease in germination percentage. Each further increment in water stress produced additional significant decreases in germination capacity. At 1.2 MPa, germination was almost prevented. Seeds pretreated before storage showed lower germination percentage and speed at all osmotic potentials, but this result was due to a marked effect of seed initial MC, rather than a lower resistance to water deficit. In fact, MC of beechnuts pretreated before storage was 8%, whereas beechnuts pretreated after storage started germination tests under water stress with an initial MC of 30%. Moreover, seeds at lower initial MC need more time to imbibe before the germination process can start. Seeds with higher initial MC were probably able to cope better with water deficit, at least during the 30-day germination test in the laboratory. A second experiment carried out on beechnuts treated only before storage but made to have different initial MC seemed to confirm this conclusion. Ungerminated seeds were not damaged, as revealed by a tetrazolium test performed at the end of each germination test. Advantages in nursery practice shown by dry, nondormant beechnuts (pretreated before storage) are discussed in relation to the possibility of sowing when water availability in the soil is not a limiting factor.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.