Bud morphogenesis of white spruce Picea glauca seedlings in a uniform environment
Differences in height growth occurring between provenances of white spruce are associated with variation in number of needle primordia formed in the dormant bud. The number is influenced by seasonal pattern of initiation. This investigation sought to establish whether normal morphogenesis could proceed in a constant environment, and whether provenance variation would be expressed in the absence of seasonal changes. Bud development was induced in five provenances of white spruce by subjecting 1st-year seedlings to short photoperiods. Developing buds were sampled at 3-week intervals over a period of 12 weeks. Throughout this time, photoperiod was kept at 8 h; temperature was constant at 22.5 °C (72.5 °F). Observations revealed a morphogenetic pattern comparable with that of buds in older, field-grown trees. Needle initiation on the primordial shoot ceased 6 to 12 weeks after the inception of bud development. The inferred endogenous control of bud development and its effect on shoot growth was influenced genetically, with significant differences in needle initiation occurring among the provenances. Differences in bud development may allow early selection for fast growth and hardiness in this species. The results of this investigation identify the period immediately after shoot growth as critical for subsequent growth of nursery stock.