In order to determine freezing tolerance of 10 rapeseed (Brassica napus L.) cultivars including Zarfam, Licord, Elit, SLMO46,Okapi, Symbol, Calvert, Opera, Ebonit and Alis, a green house experiment was carried out at the College of Agriculture, Ferdowsi University of Mashhad. In a two-replicate RCBD split factorial experiment two levels of acclimation ( acclimated vs no acclimated) served as mainplots and a combination of five cold levels (0, -4, -8, -12 and -16 °C) and the 10 genotypes served as subplots. Plants were kept until 3-5 leaf stage in greenhouse condition with 23/16 ± 2°C (day/night) and natural photoperiod. Then, the plants of non-acclimation treatment were frozen immediately and for acclimation treatment after three weeks that put them under acclimation freezing were done. Survival percentage, leaf area, SPAD reading, dry weight, (LT50)1 and (RDMT50)1 were determined after 3 weeks. Survival percentage after freezing was different in cultivars (p < 0.01). Calvert, Symbol and Zarfam cultivars had the highest (77, 76 & 75) and Opera cultivar showed the lowest (63) survival
percentage, respectively. Cultivars were different in leaf area, dry weight and LT50. The most freezing damage on the plant was absorbed at the lower than -4oC temperatures. Although acclimation decreased the freezing effects on the most characteristics. In according to the good correlation between LT50, SPAD reading, and LT50 with survival percentage, it seems that for evaluation of freezing tolerance in rapeseed using, the LT50 and SPAD reading may be useful.
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