Carl Bogdanoff,* Pat Bowen, Brad Estergaard, Steve Marsh, and Emmanuelle Jean
*Summerland Research and Development Centre, 4200 Hwy 97, Summerland / BC / V2A 8V4, Canada (Carl.Bogdanoff@agr.gc.ca)

The effects of cold temperature exposure regimes on phloem freeze injury and subsequent bud break and shoot development were determined using dormant Merlot canes. Freshly pruned canes were exposed to cold temperature treatments in a walk-in freezer programed to cool at -2 °C/hr, while bud and phloem hardiness was determined using a standard differential thermal analysis protocol. In one experiment, bundles of 13 canes were removed during the cooling ramp-down at set temperatures between -12 and -28°C. In another experiment, after the ramp-down, the freezer  temperature was held  constant at ~ 4°C above the temperature lethal to 50% of buds, during which bundles of 10 canes were removed after 0, 1, 4, 8, and 24 hrs. In both experiments, after the exposure treatments ~ half of the canes were sectioned and assessed visually for bud and phloem damage, and the rest were cultured to initiate root and shoot development.  Results indicate that budbreak and shoot development were not affected until phloem damage exceeded 80%, which occurred around the same temperature as that causing 50% primary bud mortality. The amount of bud and phloem damage increased with the duration of exposure to 4°C above the 50% bud-lethal temperature. More than 80% of phloem was damaged after 8 hrs, and 50% of buds were killed after 24 hrs exposure.

Funding Support: British Columbia Wine Grape Council and Agriculture Agri-Food Canada