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This is a Experimental Study study.

October 10, 2025

Accelerating Seedling Growth Through Photoperiod Extension for Genetic Testing: A Case Study with Blue Spruce (Picea pungens)

Key Points

Extended photoperiod allows blue spruce seedlings to reach field planting size in 6 months instead of 3 years.
Seedlings with accelerated growth maintained a significant height advantage over non-accelerated trees for 7 years.
Height growth interaction was significant for genotype and nursery treatment, particularly in early years.
Findings imply that accelerated growth via photoperiod extension could benefit spruce progeny evaluations in similar conditions.

Abstract

Abstract Extended photoperiod, frequent watering, and fertilization of blue spruce in a greenhouse produced seedlings of field planting size in 6 months, whereas similar spruce grown under outdoor nursery conditions required 3 years to reach the same size. Trees receiving the former treatment (accelerated) maintained a 2-year height advantage over those in the latter treatment (non-accelerated) through 7 years. Accelerated trees appeared to be physiologically more mature than the non-accelerated trees on the basis of foliage color development, later spring bud-burst, and greater cold hardiness. Genotype x nursery treatment interaction was significant for height growth but not for foliage color, spring bud-burst or survival. The interaction in height was strongest in the early years and diminished substantially thereafter. Most of the interaction in the early years resulted from differential response to extended and natural photoperiods. Under extended photoperiods northern and southern trees grew to about the same height, whereas under natural photoperiods the southern trees grew taller. After 7 years southern trees were taller regardless of the nursery treatment used. Within latitudinal regions, progeny groups were not different in their photoperiodic responses, but genotype x treatment interaction for height was still present. The cause of this interaction could not be ascertained. Gentoype within region x treatment interaction also diminished with age. Age-age correlations within regions were better for the accelerated trees. These results suggest that spruce progeny evaluations may be hastened by accelerating seedling growth through extended photoperiods when photoperiodic responses are similar among the progeny being tested, as may be the case when the progeny originate within a restricted range and elevation. Accelerating progeny growth by extending photoperiod may also be useful where growth rate is not an important selection criterion. Forest Sci. 31:631-643.

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