Seedling Shoot and Bud Development in Provenances of Sitka Spruce, Piceasitchensis (Bong.) Carr.

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Abstract
Growth and development of seedlings of ten provenances were compared in three investigations. The provenances ranged from Oregon to south-east Alaska and were collected for the I.U.F.R.O. International Sitka Spruce Provenance Experiment. The potential for seedling growth was studied by measuring (a) the rate of shoot growth and (b) the duration of shoot elongation. Growth rate was rather uniform, being only slightly faster among northern provenances. The duration of shoot growth, under artificial declining photoperiods was strongly influenced by latitude of origin. The critical photoperiods necessary for sustained growth in southern provenances were up to 4 hours shorter than those in northern provenances. In the third investigation development of the terminal bud was followed during the first 8 weeks. After a 4-week induction period buds attained macroscopic sizes with ca. 100 needle primordia. Northern provenances had up to 65% more primordia than southern ones. At 8 weeks, a strong but reversed relationship was evident, with southern provenances having up to 35% more than northern provenances. These observations indicate that latitude-correlated variations will be an important feature of the I.U.F.R.O. Experiment, with southern provenances performing especially well in southern trials. Potential advantages of southern provenances will be protracted periods of shoot growth in young seedlings and protracted periods of development of the primordial shoot in overwintering buds. However, where summer seasons are short, such advantages may not be realized.

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