Onset, Intensity, and Dissipation of Rest in Several Pecan Cultivars1

Onset, intensity, and dissipation of the physiological state of rest were determined in buds of several cultivars of pecan [ Carya illinoensis (Wang.) K. Koch]. ‘Stuart’ exhibited the highest rest intensity and ‘Desirable’ the least. Onset of rest in ‘Desirable’ and ‘Stuart’ buds occurred prior to the advent of chilling temperatures below 7.2°C. Further intensification of rest occurred with initial 70 hours accumulated exposure to chilling temperature. Number of days to bud break on shoots collected after 70 hours exposure to field chilling could not be reduced to that obtained before such exposure regardless of additional cold treatment until late winter. Rest intensity was sharply increased in buds of some cultivars under controlled conditions upon initial exposure to 1.2°C when petiole stumps or green fruit were present, thereafter rest was dissipated with additional cold treatment.