Effect of prechilling on the dormancy of Betulapendula seeds

The effect of prechilling on the germination response to temperature was investigated by germinating prechilled (at 5 °C) and unchilled seeds of Betulapendula Roth (silver birch) at temperatures of 10, 15, 20, 25, and 30 °C in darkness. Unchilled and prechilled seeds produced 50% germination at temperatures of 26.7 and 15.3 °C, respectively. Two experiments were organized to study the effects of a range of prechilling temperatures (0–12 °C) on release of dormancy. The level of dormancy in the seeds was tested at 12 °C using 6- and 18-h photoperiods. The optimal prechilling temperatures were between 1.0 and 3.3 °C. As the prechilling temperature increased, the effect of prechilling decreased so that the upper effective limit was between 8.7 and 12.0 °C. The effect of prechilling time on dormancy release was studied in an experiment where seeds prechilled at 2.4, 5.5, and 12.4 °C for 6, 12, 21, and 42 days were germinated at 12 °C using 6- and 18-h photoperiods. The germination probability (in logit scale) was directly related to the logarithm of the number of prechilling days. In seeds prechilled at 2.4 °C the requirement for a long photoperiod for germination was removed in 21 days, whereas 42 days were needed in seeds prechilled at 5.5 °C.