Influence of Pre- and Post-Treatment Storage on Budbreak of Hot Water Treated Cuttings of Cabernet Sauvignon

Abstract

This study examined the practical aspects of pre-, post-, and pre- plus post-treatment storage on bud survival and rate of budbreak of hot water treated dormant cuttings of Cabernet Sauvignon. Cuttings were either collected in November and stored at 3°C to 4°C until treated (pre-treatment storage) or collected monthly, from November through February, 24 hours prior to treatment. Treatments were made to cuttings removed from storage and cuttings collected the previous day. Hot water treatments consisted of 52°C, 54°C, 56°C, 58°C, or 60°C for 10, 20, or 30 minutes. After treatment, half of the cuttings removed from storage and half of those collected 24 hours earlier were placed in cold storage (3°C-4°C) until mid-February (pre-post-treatment storage and post-treatment storage, respectively). The other half of the cuttings from storage and those collected the previous day were transferred to the greenhouse (pre-treatment storage and no storage, respectively). Greenhouse samples were evaluated weekly for nine weeks to establish rate of budbreak. After nine weeks, buds of cuttings that showed no signs of growth were examined by sectioning with a razor blade and observed with a microscope for survival. In every case such buds were found to be dead. When analyzed for temperature effect only, cuttings showed good budbreak up to 56°C. The days to budbreak (DBB) increased with increasing time of treatment at all temperatures except 52°C. Cuttings taken or treated in January and that received post-treatment storage had the fewest DBB. Data analysis showed the potential for heat treating cuttings at temperatures up to 56°C, especially if this was combined with post-treatment storage at 3°C to 4°C. January was the best month to collect cuttings, as determined by the reduced time to budbreak and a decrease in the percentage of dead buds caused by hot water treatment. However, the risk of winter injury in late December and January under Washington State conditions dictates that cuttings be taken as soon as possible after leaf fall and the onset of dormancy. If hot water treatment is confirmed as a procedure for eliminating crown gall from dormant grape cuttings, the results of this study suggest that nurserymen should treat the cuttings immediately after collection and then put them into cold storage.