In 1999 and 2000, 10 varieties and lines of bread wheat of different degrees of resistance and susceptibility to cold, were crossed in a half – diallele scheme. The plant materials were cultivars Boulani, Sabalan, Khalij, Bezostaya and lines 591, 592, 273, 746, 581 and 583. The 10 parents and their 45 F1 hybrids were planted in greenhouse as well as field, at the College of Agriculture University of Tehran, Karaj, Iran. The traits of days to flowering LT50, survival at -8?C, -12?C, -16?C, membrane stability (electrolyte leakage) were assessed. Membrane stability (electrolyte leakage) of the plants was found at –12?C. Results of ANOVA showed significant differences between genotypes in 1% and 5% levels of probability. Analysis of general combining ability (GCA) and specific combining ability (SCA) through Griffing method indicated significant differences between genotypes. It was found that genes with additive as well as non – additive effects control these traits. Graphic interpretations of the results of diallele cross, by using Hayman’s method revealed that dominant genes with additive effects control cold resistance. It was found that resistant cultivars Bezostaya and Sabalan bear a large number of Dominant genes, whereas other cultivars Bolani, Khalij as well as lines 746 and 518 carry mostly recessive genes.
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