Pruning Effects on Cold Hardiness and Water Content During Deacclimation of Merlot Bud and Cane Tissues

Abstract

Computer assisted thermal analysis was used to measure deep supercooling in dormant bud and cane tissue of Vitis vinifera L. cv. Merlot during a five-week deacclimation period. The weekly low temperature exotherm (LTE), an indicator of hardiness, of both cane (internode) and primary bud tissue, responded to increases in air temperatures, with bud tissue responding faster than cane tissue. Bud tissue from pruned and unpruned canes retained the capacity to supercool until early bud swell. Cane tissue had lower LTEs than bud tissue on each date and was able to supercool past the time of bud swell. Pruning treatments did not influence the loss of hardiness in either bud or cane tissue. Water content of canes was more affected by all three factors (date, position, and pruning) than was hardiness. Bud water content was lower than cane water content for every date and each position throughout the study. Cane water content increased with distance from the trunk. Observations during the three weeks before bud swell indicate that cane tissue hydrates rapidly but dehardens only slowly, while buds deharden more quickly and yet have only a small increase in bulk water content. Pruning slowed the rate of cane hydration during the week it was most rapid, especially at the most distal position.