Bud Dormancy Status, Frost Hardiness. Shoot Moisture Content, and Readiness of Black Spruce Container Seedlings for Frozen Storage

Abstract

Black spruce [Picea mariana (Mill) B. S. P.] first-year seedlings were exposed to 8-hr photoperiods and warm temperatures (26C maximum, 15C minimum) and tested weekly to determine bud dormancy status, frost hardiness, shoot moisture content, and the amount of damage caused. by a period of frozen storage (- 3C). Bud dormancy status, frost hardiness, and shoot moisture content were all strongly correlated to the time of bud initiation. Frost hardiness was low (- 5 to - 7.5C) during the period of needle primordia initiation until week 3 (3 weeks after 100% bud initiation), but bud dormancy decreased linearly over this period, from 37 days to budbreak for seedlings sampled at week - 1 (1 week before 100% of the seedlings had initiated terminal buds) and placed under conditions favoring shoot elongation, to 14 days to budbreak for seedlings sampled on week 3. From week 5 to week 8, there was a strong (r2 > 0.999) linear correlation between frost hardiness and bud dormancy status. Shoot moisture content declined linearly from 84% on week - 1 to 74% on week 8 (r2 = 0.97), and shoot moisture content was correlated with both frost hardiness (r2 = 0.87) and the percentage of seedlings that suffered needle damage in frozen storage (r2 = 0.85). Bud dormancy status, measured as number of days to 50% budbreak, was curvilinearly correlated with seedling damage following frozen storage, whereas linear relationships with damage in storage were found for dormancy release index (r2 = 0.92) and frost hardiness (r2 = 0.85).