These data indicate the raw freezing survival scores (0=dead, 3=undamaged) of canola that was acclimated for 4 weeks at 5C and then deacclimated at the indicated times and temperatures and then frozen for 4 hours at -13C- followed by recovery for 7 days prior to scoring. The data is shown for 6 replicates for each line with the first column indicating the genotype, the number of days (column 2) at each temperature (column 3), the replicate number (column 4) the experimental run 1 or 2 (column 5) and the survival score (column 6).
Nine varieties of winter type canola with divergent freezing tolerances following cold acclimation (Chao et al., 2021) and deacclimation (Horvath et al., 2020b) were chosen from a diversity panel used to conduct genome wide association studies on freezing tolerance and deacclimation resistance (Horvath et al., 2020a). Two spring type canola (Wester and Regina II) were also used as controls. Experiments were conducted using a randomized complete block design (RCBD) with six replicates and a single plant as an experimental unit. Each experimental unit was performed two times and data for each independent experiment is presented (see: experiment I and experiment II in the results). Plants were grown in 800mL pots and potting soil (Promix from PREMIER HORTICULTURE INC) under greenhouse conditions for 4 weeks (6-8 leaf stage) at ~22°C. The photoperiod was 16 h of light with supplemental halogen lighting as needed. Plants were fertilized with 20-20-20 NPK mixed fertilizer once a week in a greenhouse and plants were watered as needed (Horvath et al., 2020a).
After 4 weeks of growth under the greenhouse conditions, plants had reached the 6 to 8 leaf stage and were moved to a cold acclimation chamber at 4-5°C with 12-h photoperiod (with supplemental full spectrum LED lighting—Lumigrow LU50001) for 4 additional weeks. Plants were then moved to a growth chamber for deacclimation at a constant temperature of 5, 7, 10, 13, & 15°C with a 12-hour photoperiod. Plants were deacclimated for 1, 2, 3, 7, & 14 days at each temperature. Plants were transferred from acclimation chambers on different days to allow synchronizing of the freezing treatment. There were 25 different treatments (5 temperatures × 5 deacclimation time points). Plants were assigned randomly to each treatment after cold acclimation. Plants were separately grouped for freezing as follows: group 1- 1, 2, & 3 days of deacclimation; group 2 - 7 days of deacclimation; and group 3 - 14 days of deacclimation. Deacclimation at 5°C is essentially the same as cold acclimation. Thus, a subset of plants (those given 7 and 14 days of deacclimation at 5°C) received 5 or 6 weeks of cold-acclimation respectively. Plants were randomly placed within the freezing chamber. Freezing treatment was initiated at around noon starting at 15°C and ramping down to 5°C over the next five hours, then ramped down to the freezing temperature (−12°C) over eleven hours (4:00 AM), and held at -12°C for 4 h before ramping back up to 0°C, over 1 hour (h), and then back up to 15°C by noon the following day (lights were turned off at 5:00 PM when plants had reached 5°C and then turned on again at 8:00 AM during the last hour of freezing temperature). Plants were moved to the greenhouse and were scored for visual damage on a 0–3 scale with 0 being dead, 1 having >50% foliar damage but maintaining at least one living meristem, 2 having between 50% and 10% foliar damage, and 3 having 0–10% foliar damage after a one-week recovery period. The whole experiment was run twice.