The objective for this work was to identify the dormancy depth and the bud-sprouting rate of pear trees kept at chilling conditions (4ºC±1) for different periods. The experiment was carried out using buds of twigs of the previous growth season from a pear orchard of the Embrapa Clima Temperado Research Center. The twigs were collected on June 1, 1999. The treatments were five period of chilling: 0 (control); 272; 544; 816; or 1088 hours at 4ºC±1. At the end of each treatment, the twigs were cut into short cuttings containing one lateral or terminal bud each and placed in controlled conditions at 25ºC± 1. The variables evaluated were percentage of bud break and period of time to reach that phase. The mean of time of bud break (MTB) for the terminal buds decreased significantly on the cuttings that received 816 or 1088 chilling hours which were equivalent on MTB. Similarly the bud break rate (time to reach 100% bud break) was significantly shorter on the buds that received 816 or 1088 chilling hours. Therefore the terminal buds of pear cv. Carrick need 800 hours for a satisfactory bud break.
Temperature; dormancy; Pyrus communis; mean time to bud break (MTB); biological method
