Freeze Duration Effects on Winter Canola at Different Growth Stages.

The winter vernalization of canola (Brassica napus L.) is a necessary step in reproduction. In the Kansas State University plant research facility an experiment was conducted to test an early fall freeze before canola plants acclimated at different growth stages.  Three varieties of canola, Sitro, Wichita, and DKW46-15 were planted in the greenhouse.  Four growth stages, cotyledon, 1-leaf, 3-leaf, and 6-leaf were tested. Temperatures of -2, -4, -6, -8⁰C were simulated in a Percival growth chamber for each growth stage. Plants were placed in agrowth chamber for three days at a temperature of 4⁰C to simulate acclimation.  The growth chamber then was programed to drop its temperature to -2⁰C over six hours. Next the temperature lowered in steps of 2⁰C over one hour followed by a one hour soak.  Plants were removed at -2, -4, -6, and -8 ⁰C and placed in a second growth chamber at a constant 4⁰C. After 12 hours all plants were returned to the greenhouse. Once the plants had acclimated for a day ratings on survival and injury wererecorded.   Three weeks later plants were rated a second time.  Plants that were froze from the -6 and -8⁰C treatments presented the greatest amount of death or injury.  From the data collected it can be concluded that canola can survive at -4⁰C when exposed to a short acclimation period.