Frost hardiness, height, and dormancy of 15 short-day, nursery-treated interior spruce seed lots

Fifteen seed lots, five each from natural-stand, seed-orchard, and full-sib collections, of interior spruce (Picea glauca (Moench) Voss, Picea engelma nnii Parry ex Engelm., and their naturally occurring hybrids) were sown in February 1993. One half of each seed lot received an ambient photoperiod (c ontrol) treatment, while the other half got a blackout (short-day) treatmen t. All seedlings were grown under ambient photoperiod except during the 17 days of blackout. Frost hardiness assessments were done between July and Ma y. Blackout treatment was effective in regulating height and promoting fros t hardiness in all seed lots, particularly vigorous ones. Seed lots origina ting from high latitude or elevation were more frost hardy both at fall lif t and spring planting. Full-sib seed lots from similar latitude displayed n o elevational frost-hardiness trend. Blackout treatment promoted seedling d ormancy (estimated with days to bud break) at lift, but it had little or no effect on dormancy at planting. Seedling dormancy and frost hardiness were acquired and lost differently, suggesting that they are independent physio logical processes. Blackout treatment significantly reduced new roots at pl anting in all lots. This could retard early field performance and negate th e apparent utility of blackout treatment.