In order to evaluate freezing tolerance of different triticale (X Triticosecale Wittmack) genotypes, an experiment was carried out under controlled conditions in 2007 and 2008 at college of agriculture, Ferdowsi University of Mashhad. In this study seeven triticale genotypes (‘Juanilo-92’, ‘ET-82-15’, ‘ET-82-8’, ‘ET-83-20’, ‘ET-83-19’, ‘ET-83-18’ and ‘ET-79-17’), across six temperatures (0°C, -4°C, -8°C, -12°C, -16°C and -20°C) were evaluated within a factorial-completely randomized design with three replications. Plants were kept until 2 leaf stage in chamber with temperature of 20/15°C (day/night) and 12.5 h photoperiod. At the end of this stage, plants were under acclimation for three weeks. After exposing to acclimation freezing the cell membrane integrity was measured through electrolyte leakage (EL) and the lethal temperature (LT50) of samples was measured. After the exposure to freezing temperatures the samples were transferred to the greenhouse. Survival percentage, plant height, leaf area and number, chlorophyll content, and plant dry weight were determined after 3 weeks. Results showed that the effect of different freezing temperature and genotypes were significant on all plant characteristics. As temperature decreased, %EL of all genotypes was increased. Minimum and Maximum EL % in leaf and crown were observed at 0°C (21%) and -20°C (88.5%). ‘ET-79-17’ and ‘Juanilo-92’ genotypes showed the highest EL% (55.5% and 44.8%) and ‘ET-83-20’ the lowest EL% (47.3% and 41.2%) in leaf and crown. Dry weight and leaf area decreased by 48% and 42% respectively compared to non frozen control plants. ‘ET-79-17’ and ‘ET-82-15’ genotypes showed the highest dry weight (83.8 mg) and highest leaf area (14.3 cm2) respectively and ‘ET-83-20’ cultivar showed the lowest dry weight and leaf area (58.2 mg and 8.7 cm2).

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