Dehardening in flower buds of saskatoon-berry, Amelanchier alnifolia, in relation to temperature, moisture content, and spring bud development

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Abstract
Flower-bud dehardening of saskatoon-berry (Amelanchier alnifolia Nutt. ‘Smoky’ and ‘Pembina’) was studied under natural and controlled conditions. Flower buds were hardy to −45 °C until the middle of March, after which hardiness gradually declined to −12 °C by the beginning of May. Petal expansion was associated with a loss of hardiness, even though bud moisture content decreased slightly. Hardiness of unopened flower buds was closely correlated with bud moisture content (r = 0.94) and under outdoor conditions there was a significant positive correlation between cumulative degree days (base 0 °C) and bud moisture content. Imbibition in gibberellic acid (GA3) increased water uptake and reduced hardiness of excised flower buds compared with imbibition in water. Treatments with abscisic acid and salicylic acid had no significant effect on hardening. Budbreak, in the postrest period, required only 73 degree day (base 2 °C) heat units. Low-temperature exotherms were not detected in intact flower buds but were present in hardy excised florets.

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