Effect of harvest date, drying, short-term storage and freezing after chilling on the germination of rowan seeds

The effects of seed pretreatment and harvest date on the germination of European rowan (Sorbus aucuparia L) seeds were examined. In one experiment, seeds were subjected to drying, storage, soaking, warm and chilling treatments after harvesting in mid- and late August. In another experiment, fully imbibed (FI) seeds were given warm treatment for six weeks and then various durations of chilling (4 +/- 1 degrees C) for up to 24 weeks. Thereafter, the seeds were adjusted to target moisture content of 35% and 30% or remained in the FI state and were then subjected to either subsequent chilling or freezing (-3 degrees C) for up to 32 weeks. The treated seeds were allowed to germinate at a constant 15 degrees C with 8 hours of lighting per day. Treatment effects were generally consistent for each harvest date. Seeds did not germinate unless they were chilled and germination rates were low unless the seeds were soaked. Warm treatment applied before chilling appeared to induce dormancy. The effect of storage varied with harvest date and storage treatment, with germination being highest for seeds harvested in late August. Mild freezing of >= 16 weeks duration following 16-24 weeks initial chilling resulted in >80% germination, more than could be achieved using chilling alone.