Apple tree demands periods of low temperatures (4ºC to 10ºC) during autumn and winter, otherwise the tree will keep under dormancy or will present an irregular shooting and blooming. Without low temperatures during autumn and winter, apple tree buds keep under dormancy during a longer period and present an irregular shooting and blooming. In order to measure the quantity of cold needed to subject the dormancy, it was used the method of number of cold unities according to the Modified Model of the North Carolina. In stakes with length from 20cm to 25cm, and in stakes of isolated knots, which received from zero to 530, 1,060 and 1,590 cold unities during the dormancy. Tried cultivars were Condensa, Baronesa, Daiane, Imperatriz, Gala and Fuji. Cultivars differed themselves on the number of days for the shooting of the buds, taking place the minor time for shooting when they were subjected to 1,590 cold unities, for all the cultivars, what showed that there's a tie between the average time of the shooting and the deepth of the dormancy. The percentage of shoot buds was also larger when the stakes were exposed to 1,590 cold unities, being Condensa the cultivar that showed the largest percentage of shooting, what confirms that it is really, among the studied cultivars, that of minor demand in cold.
dormancy; Malus domestica; chilling unities; bud breaking
