Abstract
Seven potted dormant tetraploid grapevine cultivars grown under forced conditions were treated immediately after pruning with the supernatants of a 20% suspension of CaCN2, 2% H2CN2 and 5% diallyl disulfide in different chilling exposures: late November (73 hours), early January (620 hours) and late February (1,275 hours). The effectiveness of the chemicals in initiating budbreak was assessed by the number of days to initial and 60% budbreak after treatment, indicating the promotion and uniformity of budbreak, respectively. Although the chemicals were most effective when applied in November, there was large variation in the response of buds among cultivars and treatment times. For November treatment, H2CN2 was the most effective in accelerating budbreak initiation and enhancing uniformity for almost all cultivars, followed by CaCN2, whereas in the January and February treatments, there were no differences in the promotion and uniformity of budbreak between the two chemicals. Response of buds to diallyl disulfide varied largely among the cultivars. Diallyl disulfide delayed budbreak initiation or reduced percentage budbreak for ‘Aki Queen’ and ‘Takatsuma’ in all the treatment times and for ‘Pione’ in November and January treatments. For ‘Fujiminori,’ there was no significant difference in the effectiveness of chemicals on budbreak regardless of treatment time. We conclude that H2CN2 is the most effective chemical for budbreak of tetraploid cultivars, followed by CaCN2, and diallyl disulfide. However, the response of grapevine buds to chemicals varies with the depth of dormancy and cultivar.
