Photoperiod effects on cold acclimation of grape rootstocks

The photoperiod is the only stable climatic index for perennial species to sense the time of year and initiate physiological processes to allow winter survival. Various species of Vitis have shown differences to acclimation and cold hardiness in response to photoperiod changes. This experiment evaluated photoperiod response of 4 rootstocks of Vitis: Riparia Glorie (V. riparia Viala), C- 1613 (V. solonis Prince ex Bailey x 'Othello' {V. labrusca L. x V. riparia Michx. X V. vinifera L.), St. George (V. rupestris Scheele), and Cabernet Sauvignon (V. vinifera L.). The experiment was conducted on cuttings in the greenhouse and on mature vines in the field. The genotypes received 3 treatments (16h light/8h dark, 12h light/12h dark, and 10h light/14h dark) using a completely randomized block design, Evaluation of photoperiod response was based on tests performed over a 5-week period when the treatments were applied. Tests performed included measuring tissue relative water content, measuring rate of leaf maturation and stem elongation, and observing periderm formation. Thermocouple psychrometers were used to measure osmotic potential and calculate the freezing point depression of bud tissues. Photoperiod significantly (P = 0.05) affected acclimation when evaluating freezing point depression and periderm formation. Genotype also significantly affected acclimation when evaluating periderm formation. Freezing point depression showed more consistent results than relative water content. Therefore, freezing point depression may be a more reliable test for evaluating acclimation in response to photoperiod. Tests indicated that 'C-1613' showed a greater and more consistent response to changes in photoperiod when measuring relative water content, freezing point depression, and periderm formation. As a result, 'C-1613' may be a good choice for future studies in the acclimation of Vitis. However, its complex parentage will pose problems for genetic analysis..