The effects of temperature on budbreak of cuttings obtained at different stages of dormancy from 'Pione' grapevines (Vitis labrusca × V. vinifera) grown in open field were investigated. Cuttings were collected at monthly intervals from July to March. Judging from the number of days to initial and 60% budbreak after treatment, indicating promotion and the uniformity of budbreak, respectively, 30℃ was the most effective in budbreak, followed by 25 and 20℃ in that order in all treatment times. However, the effect of temperature on budbreak was markedly affected by treatment time. The number of days to initial budbreak (NDIB) increased gradually from July to October, peaked in December and thereafter decreased gradually towards March. The periods from July to September, from October to December, and from January to March were assumed to correspond to paradormancy, endodormancy, and ecodormancy of 'Pione' grapevines, respectively. Final percentage of budbreak was less than 100% until endodormancy for all temperatures. It was below 60% at 20℃ treatments of July to September. On the other hand, a uniform budbreak was observed in the treatments after the middle of endodormancy for all temperatures, resulting in almost 100% of final percentage of budbreak. There was a significant negative correlation between NDIB and cumulative chilling hour (CCH) of exposure to below 7.2℃ in the treatments after November, and also between NDIB and cumulative temperature (CT, ℃･h), a summation of temperature and hours of exposure to above 0°C from November 1 to each treatment time and hours of exposure to 20, 25, or 30℃ from start of treatment
to budbreak in each plot. The results suggest that besides CCH, CT can also be used to estimate the completion of dormancy in 'Pione' grapevine bud.
breaking of grapevine bud
cumulative chilling hour (CCH)
cumulative temperature (CT)
different dormant stages