Effect of Chilling and Photoperiod on Budbreak in Three Hybrid Grape Cultivars

The present study assessed the effect of photoperiod on budbreak of cuttings of three interspecific hybrid grape (Vitis) cultivars that had received different chilling hours. Stem cuttings were collected at 100-hour intervals of chilling (200, 300, 400, 500, 600, 700, and 800 hours) from the vineyard and kept in three growth chambers with daylengths of 8, 16, and 24 hours. Another group of cuttings were maintained in a greenhouse with a natural daylength range of 10.513 hours [8 Dec. 2017 to 4 May 2018 (average = 12 hours)]. Chilling requirements, days to budbreak, and budbreak rate were determined after plants were exposed to different chilling hours and daylengths. Results of our study demonstrated that the chilling requirements of all three cultivars were adequately reached at 600 hours or more. Increasing chilling exposure from 600 to 800 hours shortened the time to budbreak in all cultivars. Overall, `MidSouth' had an average budbreak rate of 90% when receiving at least 600 hours chilling. 'Blanc du bois' and 'Lake Emerald' had 62% and 65% average budbreak, respectively. Longer days (24 hours) reduced time to budbreak by 14, 6, and 8 days, respectively, in 'Blanc du bois', 'Lake Emerald', and `MidSouth' at 600 hours chilling. A combination of 24-hour photoperiod and chilling of 600 hours resulted in a maximum budbreak rate of 70%, 70%, and 100% in 'Blanc du bois', 'Lake Emerald', and 'MidSouth', respectively. Our results indicate that breaking dormancy may be controlled by both temperature and photoperiod in these three cultivars.