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The effect of moisture content and prechill duration on dormancy breakage of Douglas fir seeds (Pseudotsuga menziesii var. menziesii [Mirb.] Franco)

Published online by Cambridge University Press:  22 February 2007

Peter G. Gosling*
Affiliation:
Silviculture and Seed Research Branch, Forestry Commission Research Agency, Alice Holt Lodge, Farnham, Surrey GU10 4LH, UK
Yvonne Samuel
Affiliation:
Silviculture and Seed Research Branch, Forestry Commission Research Agency, Alice Holt Lodge, Farnham, Surrey GU10 4LH, UK
Andrew Peace
Affiliation:
Silviculture and Seed Research Branch, Forestry Commission Research Agency, Alice Holt Lodge, Farnham, Surrey GU10 4LH, UK
*
*Correspondence Fax: +44 (0)1420 23653, Email: [email protected]

Abstract

Seeds of Douglas fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco) were initially germinated at six constant temperatures (10–35°C), following 0–48 weeks incubation under moist conditions at 4°C, i.e. prechill or stratification. The best, single germination temperature was 15°C for determining the efficacy of subsequent dormancy breakage treatments. Seeds from the same seedlot were then adjusted to 10, 15, 20, 25, 30, 35 and 40% moisture contents (mcfw, fresh weight basis), prechilled for 0, 2, 4, 8, 16, 32, 64 and 128 weeks and transferred to 15°C. A smoothed bivariate spline was used to model the results and showed that virtually all combinations of moisture content and prechill duration significantly stimulated germination capacity, but that the optimal germination percentage (≥93%) was stimulated only by various combinations of between 30 and 35% mcfw and 25 and 48 weeks prechill. At optimal moisture contents (30 and 35%) , extending the prechill duration beyond 48 weeks led to a decrease in germination capacity. This was not due to dormancy reintroduction, but was caused largely by seed death. Regression models using a weighting function, to account for differences in standard deviations, demonstrated significant increases in the mean moisture content of individual seeds at higher moisture contents (≥25%) and longer prechill durations (≥64 weeks) that were concomitant with significant decreases in dry weight. The most likely explanation for this was seed respiration. The combined results suggest that dormancy breakage in Douglas fir seeds requires a hydration level sufficient for respiration to take place, and that, after maximal dormancy release, seeds at the highest mc (35–40%) exhaust their food reserves and begin to deteriorate.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2003

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