Dormancy and Acclimation in Dogwood Clonal Ecotypes
Stevenson, Robert Kenneth
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Timing of vegetative maturity (VM) attainment and cold acclimation/hardiness development were compared in red-osier dogwood (Comus sericea L.) ecotypes under field, shadehouse and controlled environment conditions. Controlled environment studies were also used to evaluate the efficacy of photoperiod/temperature regimes on attainment of VM in these ecotypes. Finally, the influence of turfgrass on VM attainment was examined. Tests made use of dogwood ecotypes from Utah, Massachusetts (Mass), Chalk River (CR), Saskatoon, Northwest Territories (NWT) and Alaska. Under all systems, the northern ecotypes (Alaska and NWT) attained VM first. Order of VM attainment was consistent between systems. Certain southern ecotypes (Utah and CR) did not attain VM under Saskatoon conditions, however, all plants survived winter temperatures lower than -30°C. Controlled environment studies indicated that northern ecotypes can be induced to true VM by either short days (8 hr), low night temperatures (5°C), or a combination of both. The more southern ecotypes required short days for VM induction, but low temperatures could enhance earliness of induction. Low temperatures in the absence of short days were not effective for southern ecotypes. Controlled freezing studies of short day/warm temperature (SD/WT) treated plants indicated that all tested ecotypes acquired a high degree of acclimating ability prior to the attainment of VM. Following 4 weeks of acclimation, hardiness levels at budset (prior to VM) exceeded -22°C. Planting of dogwoods into established turf led to early growth cessation, but not dormancy induction. Turf-grown dogwoods had stunted growth and winter damage, while control plants exhibited none of these problems.