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Coniferous tree seed germination with particular reference to the effects of temperature, seed moisture and stratification on germination behaviour of western hemlock seed Bientjes, Willem

Abstract

In a study of the problems met in testing germination of coniferous tree seed, special attention is given to the variability between different seedlots of the same species. Known and suspected causes for this variability are discussed. These include seed source, genetic constitution of individual trees, seed maturity, treatments during the commercial extraction process and storage conditions. Loss in seed viability may occur during anyone of several phases of the extraction process, such as cone storage, kiln drying and dewinging. In the discussion of the germination test procedure the importance of a moist-cold pretreatment or "stratification" is indicated. It is shown, that many species of coniferous seed are subjected to such treatment in nature. The desirability of stratification of coniferous seed as a standard pretreatment prior to incubation is emphasized. The effect of stratification on temperature and light requirements is discussed for Douglas fir in particular. The usual methods for stratification and their disadvantages are described. In order to overcome some of the disadvantages of the older stratification methods, particularly the lack of control over seed moisture content, the "naked stratification" method was developed at the University of British Columbia. This method has been applied successfully to Douglas fir seed and seed from several other species. A detailed description is given of an experiment, designed to develop a standard germination test for western hemlock seed. This involved determination of an optimum incubation temperature, seed moisture content and stratification period. The "naked stratification" method was used. The effect of incubation temperature, seed moisture content and stratification on the final germination percentage and the rate of germination was evaluated, using analysis of Variance and the t-test. The results showed, that for germination of western hemlock seed the following treatments are most favourable. Stratification for 7 — 9 weeks with a seed moisture content of 50 - 75 percent,—which is obtained after approximately 33 hours of soaking,—followed by incubation at a constant temperature of 20°C. Under these conditions the germination test can be concluded in approximately 20 days. Different incubation temperatures influenced both final germination percentage and rate of germination. Different seed moisture contents and stratification periods generally did not affect the final germination percentage, but did have a pronounced effect on the rate of germination. Stratification did not seem to change the temperature requirements of western hemlock seed. Differences in the germination behaviour of the four seedlots tested were observed.

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