Grapevine buds have a distinctive cold acclimation and deacclimation pattern. Whether these patterns also occur in roots is unknown. While direct yield loss is distinct when buds are damaged, grapevine root damage can be equally devastating: delayed or uneven budbreak, weak shoot growth, and canopy collapse. If root cold hardiness thresholds and/or acclimation patters were better understood, mitigation strategies could be developed to reduce the likelihood of root damage. This study had two major objectives: (1) to define whether roots have the ability to acclimate and (2) to elucidate their maximum cold hardiness. Due to the lack of clear protocols for assessing grapevine root cold hardiness, simultaneous protocol optimization and cold hardiness evaluations were done on potted Vitis vinifera Merlot and Chardonnay grapevines. To determine whether grapevine roots acclimated in response to their environment, three different preconditioning regimens were used: ambient air temperature when vines were actively growing, 12°C for a minimum of one week during dormancy, and 0°C for a minimum of one week during dormancy. After each preconditioning regime, root samples were taken and subsequently exposed to programmed temperature regimes of either -2.0, -4.0, -6.0, or -8.0°C. Electrolyte leakage, the gold standard in root cold damage studies, was used as the primary index of damage while low temperature exotherms (collected through differential thermal analysis) were measured as a potential alternative for assessing damage. Overall, Chardonnay and Merlot root systems did not have drastic acclimation patterns: little variation in absolute cold hardiness was seen regardless of preconditioning (<1.2°C). Maximum root cold hardiness was experimentally derived for both varieties (Chardonnay median -5.9°C, Merlot median -5.7°C). Additionally, we found differential thermal analysis an effective means to determine the temperature at which grapevine roots are damaged by cold.

Funding Support: Washington State University Department of Horticulture, Washington State University Viticulture and Enology Program, Washington State University Irrigated Agriculture Research and Extension Station