Abstract
Abstract Dormancy (absence of budbreak) in Amelanchier alnifolia Nutt., was greatest from 1 September to 13 October 1981 in ‘Smoky’ and from 1 September to 27 October 1981 in ‘Pembina’. About 576 hours for ‘Smoky’ and 696 hours for ‘Pembina’ at 0° to 7°C, were required to break bud dormancy. One week of additional chilling (3°) had little effect during deep rest, but had a significant effect when the rest requirement was nearly satisfied. Flower bud hardening began in early September and attained –44° LT50 for florets on 30 October. Vascular connective tissue at the base of the bud was less hardy than floral primordia, throughout the dormant season. Flower buds dehardened from –60° to –30° after exposure to 20° for 7 days, to –14° after exposure to 20° for 14 days. No low-temperature exotherms were detected.
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