Photoperiod Influences Growth, Bud Dormancy, and Cold Acclimation in Vitis labruscana and V. riparia

The grape species Vitis labruscana Bailey and V. riparia Michx. were subjected to a decreasing photoperiod at constant moderate temperatures to determine whether acclimation occurred in response to a shortening photoper- iod. Cane growth, periderm development, killing temperature of the primary bud, and bud dormancy were measured in vines receiving a natural photoperiod (ND), a simulated long photoperiod of 15 hours (LD), and shorter photo- periods of 14, 13, or 12 hours (SD). The LD treatment was effective at maintaining growth and inhibiting periderm development and the onset of bud dormancy in V. labruscana. Cane growth rate with all SD treatments decreased as compared to the LD regime. A significant increase in periderm development occurred with the 12-hour SD treatment. Similarly, the onset of bud dormancy was promoted by the 12-hour SD in V. labruscana. The primary bud killing temperature was 1C lower in V. labruscana under the 12-hour SD than under the LD treatment. In contrast, the LD treatment neither maintained growth nor fully inhibited periderm development and the onset of dormancy in V. riparia. The decrease in the cane growth rate upon exposure to SD was significantly greater in V. riparia than V. labruscana. Periderm development was observed in both the SD and its respective LD-treated V. riparia vines. However, the rate of periderm development was significantly greater in the SD vines than in the LD vines. The onset of bud dormancy was promoted by 13-hour SD in V. riparia. Similarly, the primary bud killing temperature was 2 to 3C lower in V. riparia upon exposure to SD. Vitis riparia has a longer critical photoperiod than V. labruscana and appears to be more sensitive to changes in light intensity or light quality. While the change in freezing tolerance in response to short photoperiods is small, the photoperiod response at a longer critical photoperiod, when combined with lower temperatures, will promote an earlier and possibly more rapid cold acclimation in V. riparia than in V. labruscana. The influence of a decreasing photoperiod or SD on growth and the onset of cold acclimation is documented for many woody species (Nitsch, 1957b; Vince-Prue, 1975); however, little in- formation exists for grapes. Woody trees and shrubs manifest responses to SD in several ways—decrease in stem growth rate, decrease in cambial activity, growth cessation, terminal bud set, onset of cold acclimation, and development of bud dormancy (Nitsch, 1957b; Vince-Prue, 1975). Under SD, apples (Malus domestica Borkh.) and dogwood (Cornus sericea Michx.) cease growth, develop a terminal bud, and begin to acclimate to low temperatures (Fuchigami et al., 1971; Howell and Weiser, 1970). Vitis vinifera L. 'White Reisling' acclimates little in response to SD, but SD combined with decreasing temperatures increases acclimation or freezing tolerance (Schnabel and Wample, 1987). In V. labruscana 'Concord', vines under natural decreasing pho- toperiod and temperatures and those under these conditions plus an incandescent light night interruption showed little difference in acclimation (Wolpert and Howell, 1986a). However, the vines receiving the night interruption treatment had more actively growing shoots than those under the natural photoperiod. Our field observations indicated that V. labruscana may not respond as quickly to the natural decreasing photoperiod in Au- gust and September as does V. riparia. The objectives of this study were to determine whether vines of V. labruscana and V.