No abstract

The effects of seed moisture content (MC) and heat treatment on the germination response of common alder (Alnus glutinosa) and downy birch (Betula pubescens) seeds were examined. Seeds of each species were adjusted to MC of 7% to 50% MC, then chilled for up to 36 weeks, after which they were allowed to germinate at 15°C with 8 hours lighting per day or 20 (dark)/ 30°C (light). Seed lot effects were evident, but treatment effects were consistent in each lot and species. The response to moist chilling treatments was larger at 15°C than at 20/30°C. Chilling had no effect on germination unless seed MC was >15%, but it was low also at 20% MC. The highest germination was achieved following 24-36 weeks chilling at the optimum or target MC (TMC) levels of about 30% in alder and 35% in birch. In a separate experiment, seeds were fully imbibed (FI) (~50% MC; standard method used in operational practice) or adjusted to TMC levels, after which some seeds of each treatment group were chilled to release dormancy. Following this, the seeds were dried back to TMC levels and then subjected to 60°C for up to 4 hours after which they were allowed germinate under the same conditions described above. Heat treatment damaged the prechilled FI seeds, but no damage occurred to the non-chilled seeds. However, heat stress stimulated germination in the non-chilled FI seeds of both species and the TMC seeds of alder.

-The effects of seed moisture content (MC), gibberellic acid (GA 3 ) concentration, chilling and priming pretreatments on the germination of common alder (Alnus glutinosa) and downey birch (Betula pubescens) seeds were examined. After treatment, the seeds were allowed to germinate for 42 days at 15• C or 20. Treatment responses were similar at both temperatures and in both species. GA 3 treatment of seeds in fully imbibed (FI) state for 30 days, or at the lower, target moisture content (TMC) for 30−90 days, significantly improved germination, but longer treatment periods reduced it (FI seeds) or had no effect (TMC seeds). Priming for two days improved germination in the FI seeds, but more than 4 days reduced it. Priming for up to 14 days had little effect on the germination of the TMC seeds.

The response of alder (Alnus glutinosa (L.) Gaertn.) and birch (Betula pubescens Ehrh.) seeds to freezing temperatures was assessed. Seeds were fully imbibed (FI) or adjusted to target moisture contents (TMC) of 30% (alder) or 35% (birch) and then chilled (4 °C) for various periods. Some seeds were redried to <12% moisture content before freezing. The seeds were germinated at 15 °C with 8 h of lighting after freezing. In the first experiment, rapid freezing at –12 °C was used to assess seed vigour. Freezing reduced percentage germination in the moist (non-redried) FI seeds, especially in those that received the longest prechilling. Freezing had a smaller effect on the TMC and the redried seeds. In the second experiment, seeds were stored for up to 60 weeks at –3 °C. Seeds stored for 60 weeks were tested also at 20 °C (16 h dark) : 30 °C (8 h light). Good germination potential was maintained for up to 12 weeks of storage regardless of pretreatment, but it declined rapidly thereafter in the moist FI seeds. Moist TMC seeds maintained good germination potential throughout the 60 weeks of storage. Germination potential declined greatly following 24 weeks of storage in the redried seeds, but the redried seeds germinated well at 20 °C (16 h dark) : 30 °C (8 h light) following 60 weeks of storage.

The response of common alder [Alnus glutinosa (L.) Gaertn.] and downy birch (Betula pubescens Ehrh.) seeds to germination temperature was examined following chilling and priming. Seeds of two seed lots of each species were subjected to combinations of chilling (4918C) and priming (208C) treatments in fully imbibed (FI) state or a lower target seed moisture content (TMC) level (30% and 35% in alder and birch, respectively). After treatment, the seeds were allowed to germinate for 56 days at constant temperatures of 7.5, 10, 15, 20, 25 or 308C. The response to temperature and pretreatment differed between species, but the effect was consistent in each seed lot within each species. In alder, the TMC seeds germinated well across the full range of temperatures, whereas there was an optimum temperature (22 Á238C) for seeds given the FI pretreatment. Priming had no significant effect on the germination response of the TMC seeds in alder, but priming greatly improved germination in the FI seeds, especially at the lower germination temperatures (optimum 18 Á198C). In contrast, in birch, the TMC seeds germinated better across the full temperature range, but the optimal germination temperature (158C) was the same for all seed pretreatments. Priming improved germination in both the FI and TMC seeds in birch.