Chilling temperature and duration interact on the budbreak of 'Perlette' grapevine cuttings

A factorial experiment examined the interaction between chilling temperature (0, 2.5, 5.0, 7.5, and 10 degrees C) and duration (50, 100, 200, 400, and 800 hours) on the budbreak of 'Perlette' (Vitis vinifera L.) grapevine cuttings. Cuttings stored at 0 degrees C exhibited the most rapid budbreak during the first 30 days after being placed under forcing conditions, lifter this period, chilling temperature had relatively little influence on cumulative budbreak, with cuttings stored between 0 and 10 degrees C generally exhibiting similar rates of budbreak. In contrast, the slope of the budbreak curves increased, indicating more rapid and uniform budbreak, with increased chilling duration. Significant interactions (P less than or equal to 0.0001) between chilling temperature and duration were found for both the number of days required for 50% budbreak and total observed budbreak. The number of days required for 50% budbreak declined, while total observed budbreak increased, with increased chilling duration. Within the temperature range evaluated, a minimum exposure of 200 hours was required to achieve commercially acceptable levels of budbreak.