Effect of long-phase stratification treatments on seed germination in ash

Abstract

Ash (Fraxinus excelsior L.) seeds require warm treatment followed by cold treatment to release dormancy and this is most effective if carried out in a medium. The objective of this study was to determine if long periods of warm treatment would enhance germination at 15 (8-h light)/5°C (dark) and 15°C (same lighting conditions) in ash seeds of north-western European origin. Ash seeds were fully imbibed (57% moisture content (MC)) or adjusted to 45% MC either in a medium or without a medium for 10–30 weeks of warm treatment, followed by 10, 20 or 30 weeks of chilling. Germination increased at both germination temperature regimes as the duration of warm treatment increased up to 18 (with medium) or 20–30 (without medium) weeks, well after the embryo had completed development (14 weeks). The response to 20 or 30 weeks of chilling was better than that of 10 weeks of chilling, but the impact of chilling was smaller than that of warm treatment. Seed MC did not significantly affect germination, but it reduced mould growth. A long warm treatment (followed by cold treatment) without a medium is the recommended treatment for ash seeds.