Cold Tolerance in Oilseed Rape over Varying Acclimation Durations

Winter rapeseed (Brassica napus L.) promises to be an important crop in the southern Great Plains. To increase the crop's consistency in the region, cultivars with improved winter hardiness and management recommendations that utilize all of a genotype's winter hardiness need to be developed. Better understanding of the variability in cold tolerance over the winter season need to be determined to help achieve these goals. The objectives of this study were to evaluate variability in cold tolerance over prolonged acclimation durations in oilseed rape by means of laboratory freezing tolerance procedures, and determine changes in freezing tolerance brought about by high temperature treatments. A warming period to simulate possible deacclimation events was included both before and after vernalization saturation had taken place. Maximum cold tolerance was achieved by 3 d of acclimation in the spring cultivar and between 6 and 9 d in the winter cultivars. A 7-d warming period reduced cold tolerance in all lines tested, but it did not reduce cold tolerance to the level of unacclimated plants. All tested lines were able to recover cold tolerance to the same level as before the deacclimation treatment after reexposure to 5°C conditions for 7 d. Cold tolerance did tend to decrease with prolonged acclimation durations. This information can help in the planning of strategies to develop rapeseed lines better adapted to the winter conditions of the southern Great Plains.