Articles
BUD DORMANCY DEVELOPMENT IN THE COLD-DEPRIVED WALNUT TREE (JUGLANS REGIA L.)
Potted trees were transferred to an air-conditioned greenhouse (minimum temperature 15°C) after varying periods of exposure to ambient cold temperatures.
At regular intervals, the dormancy of isolated buds was measured by their growth ability, expressed by means of the time they required for breaking on single node cuttings at 25°C.
The results of the greenhouse treatment depended mainly on the date when the walnut trees were transferred to the heated greenhouse, but there was also obviously a seasonal effect.
When the trees were transferred in September or October, i.e., during the onset of dormancy, the intensity of rest was first either considerably reinforced or decreased according to the dormant season examined.
In both cases, dormancy finally diminished slowly but with great variability of bud behaviour in comparison with control trees maintained continually outdoors.
Budburst on the trees was uneven and much delayed.
The transfer effected in December, at the beginning of the breaking of dormancy, slowed the decrease of rest.
The variability of bud growth ability remained high until the natural budburst on the trees which was delayed compared with the control trees.
The pattern of budburst was not as uneven as that on the trees transferred in September and October.
The transfer effected in January led to an acceleration in the decrease of dormancy.
The variability of bud behaviour and the pattern of budburst on the trees were similar to those observed in the control trees.
For trees transferred to natural conditions after varying periods of exposure to mild temperatures in the greenhouse, the different patterns of dormancy obtained after each transfer showed that the physiological state of buds could continually change even in the absence of chilling temperatures.