Cold Hardiness of Vitis vinifera Roots

Grapevine buds have identifiable patterns of cold acclimation and deacclimation, but it is not known whether roots also follow these patterns. A better understanding of root cold hardiness thresholds and/or acclimation patterns would enable mitigation strategies to be developed to reduce the likelihood of root damage. This study had two major objectives: 1) to improve protocols for electrolyte leakage and then quantitatively compare the results to differential thermal analysis; and 2) to quantify whether Vitis vinifera roots acclimate to preconditioning temperatures. Existing protocols were optimized and root cold hardiness was evaluated on own-rooted Vitis vinifera Merlot and Chardonnay. To determine whether grapevine roots acclimate to their environment, three preconditioning regimes were applied: ambient air temperature during active vine growth; 12 degrees C for one week during dormancy; and 0 degrees C for one week during dormancy. Following preconditioning, root samples were collected and exposed to fixed temperatures of -2.0, -4.0, -6.0, or -8.0 degrees C, and electrolyte leakage, the standard indicator of root cold damage, was measured. The incidence of low temperature exotherms from differential thermal analysis was used as a potential alternative to identify temperatures that cause tissue damage. Overall, Chardonnay and Merlot roots did not have dynamic cold acclimation patterns like grapevine buds. There was little variation in maximum cold hardiness (<1.2 degrees C) regardless of preconditioning. Max root cold hardiness was experimentally derived for both varieties (median = -5.9 degrees C for Chardonnay and -5.7 degrees C for Merlot). Differential thermal analysis was an effective alternative method to electrolyte leakage for estimating damage thresholds for these varieties. The lethal temperature at which 10, 50, and 90% of roots were killed was calculated for grapevine roots, with values of -4.0, -5.8, and -7.0 degrees C, respectively.