Seasonal Deacclimation Patterns of Three Grape Cultivars at Constant, Warm Temperature

¹ Virginia Agricultural Experiment Station: Winchester, 2500 Valley Ave., Winchester, VA 22601.

Dormant buds of three grape cultivars were held at 23°C at various times throughout three dormant seasons to determine how cultivar and time of season affected the extent of deacclimation as determined by thermal analysis. Cultivars examined, in order of decreasing cold hardiness, were Concord (Vitis labrusca B.), Riesling (V. vinifera L.), and Cabernet Sauvignon (V. vinifera L.). Buds of all three cultivars lost hardiness, regardless of the time of season, when held at 23°C for up to 16 days. Deacclimation rate tended to increase as the winter progressed. Among cultivars, Concord deacclimated most rapidly, Cabernet Sauvignon most slowly. Relative differences in deacclimation rate under controlled conditions paralleled differences observed under field conditions. Immersing buds in 47°C to 50°C water for two hours accelerated the loss of hardiness and reduced bud break by 15 to 25 days when buds were collected in October. Days to 50% bud break was unaffected by hot water when buds were collected in November or January; however, hot water-treated Concord and Cabernet Sauvignon buds deacclimated more rapidly than control buds when collected and treated in January. No evidence was found for a stable hardiness level in mid- to late-winter under controlled deacclimation conditions.

Key words: cold hardiness, deacclimation, dormant buds, endodormancy, bud break

Submitted on June 14, 1991