Chill Requirements to Break Dormancy of Wisconsin Cranberry: Conventional Models may Not be Applicable

Abstract

Conventional chilling models developed primarily for deciduous fruit crops such as apple and peach are based on the accumulation of optimal chilling temperatures between ≈4 and 7 °C. Cranberry (Vaccinium macrocarpon) is a perennial evergreen woody vine that requires chilling temperatures to overcome its dormancy. Periodic collections of budded stems (uprights) from cranberry beds (cv. Stevens) in central Wisconsin throughout the fall and early winter were forced to determine when dormancy requirements were met in the field. For this purpose excised uprights were placed in deionized water in test tubes at 24 °C and 16-h day (cool-white fluorescent). In both 1996 and 1997 it was observed that uprights were able to break bud and grow in late fall and early winter only after experiencing (in addition to chilling) a prolonged period of temperatures slightly below freezing. As an evergreen plant, cranberry may be receiving critical environmental cues at its leaves. Additionally, the existence of the native cranberry plant in harsh winter environments may have resulted in the need for freezing temperatures during dormancy to ensure survival.