Evaluation of Cold Tolerance of Coleoptile Growth In Some of Rice Cultivars at Germination Stage

In this research the effects of cold were evaluated on coleoptile growth of 18 rice genotypes in two separate experiments. The first experiment was carried out as factorial based on randomized complete block design with three replications. In this experiment، two factors were including genotypes at 18 levels and temperature at 5 levels (9، 13، 17، 21 and 25 C°). The seeds of genotypes don’t germinate at 9 C°. The length of coleoptile was measured in plantlets at the end of using of each temperature factor. Analysis of variance revealed that the effect of temperature، genotype and interaction effects of two factors were significant on length of coleoptile at 1% probability levels. The low temperature treatments decreased the growth of coleoptile in all of the studied cultivars. Taichung and Sadri showed a significantly bigger coleoptile length at the three low temperature treatments including 13، 17، 21 and 25 C°. The percentage of coleoptile reduction was calculated form comparison of the length of coleoptile at 13 and 25 C°. The coleoptile reduction rate was lower than 10 percentages in Hashemi، Gerde and Neamat، indicating these varieties as tolerant varieties to cold stress. Second experiment was carried out on randomized complete block design with three replications. In this experiment، the seeds were placed in 25 C° for 72 h and then the temperature was adjusted to 10 C° for 96 hr. Temperature was further increased to 25 C° and treated plantlets to this temperature for 72 h. The length of coleoptile was measured in two stage contain after 10 C° for 96 hr (length 1) and 25 C° for 72 hr (length 1). The difference between these two lengths were calculated and called coleoptile regrowth. Analysis of variance indicated that the effect of genotype were significant on coleoptile regrowth. Gerde was as a tolerant variety due to percentage of reduction in coleoptile length and coleoptile regrowth.