The effects of temperature on dormancy loss, germination and viability were investigated in seeds of Aesculus hippocastanum L. harvested over a 4-year period. Release from embryo dormancy in freshly harvested seeds was manifest in two phases of morphological growth: initially, when the seed lot was only partially released, axis emergence resulted primarily from cotyledonary petiole extension without radicle extension; subsequently, when the seed lot was totally released, axis emergence of all seeds was followed immediately by extension to >1 cm through growth of the radicle. Germination (axis emergence and radicle extension) at 16°C was a function of pre-treatment period at 2-11°C. The rate of dormancy loss (probit germination d~1) increased linearly below a ceiling temperature for the chilling response; this temperature was estimated to vary from 13°C to 16°C for two seed lots harvested in separate years. Dormancy periods for individual seeds within both seed lot populations can be described by cumulative normal distributions; the predicted standard deviation of chilling units below the ceiling temperature (i.e. thermal time) was 186°C d. Visible germination occurred during the process of stratification at 2°C, starting after 21-25 weeks. By contrast, three years of hy-drated seed storage at 16°C, which was a non-permissive temperature for dormancy loss, resulted in little preemergence of the axis during stratification; approximately one third of the seeds remained germinable. The implications of these quantitative analyses of the physiological processes in recalcitrant seeds for the development of improved storage methods are discussed.
S U M M A R YRelationships between seed moisture content (fresh weight basis) and germination were examined for nine Araucaria species by desiccation under mild environmental conditions. The lowest safe moisture content, below which germination percentage begins to decline, was estimated in each case. Seeds can be grouped into three moisture content categories: the first group (including A. araucana, A. angustifolia, A. hunsteinii and A. bidwillii) cannot be safely dried to below 25-40%; the second group (including A. columnaris, A. rulei, A. nemorosa and A . scopulorum) cannot be dried to below about 12% without damage; the third category contains A . cunninghamii, which can be dried to 2% without damage.Seeds in the first group should be stored at 0-5°C with moisture contents above the lowest-safe value. Provided freezing damage does not exceed lo%, seeds in the second group should be kept at -18°C or lower with about 7% moisture content for long-term storage and at 0-5°C with about 12% moisture content in the short term. Seed of A . cunninghamii is best retained at near 5% moisture content and in -18°C or lower.The lowest-safe moisture content was found to be associated with seed size and weight, higher moisture content values coinciding with greater size and weight of seed. Food reserve materials also differed among the groups; seeds of the first group were mainly starchy, whilst those in the other categories possessed a high lipid content.
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