influence of vernalization on some physiological characteristics and cold tolerance in two susceptible and tolerant cultivars of bread wheat

the process of adaptation to cold is an important mechanism in wheat cultivars to tolerate cold stress. this work was aimed to calrify the relationship between vernalization requirement with cold tolerance by assessing physiological changes in cold susceptible spring and tolerant winter wheat (triticum aestivum, cvs. kohdasht and cheyyene, respectively) in environmentally controlled conditions, using factiral experiment on the basis of completely randomised design (crd). by using final leaf number (fln) method, the vernalization saturation and by using lt50, the level of cold tolerance were determined in both wheat cultivars. fln results verified no vernalization requirement in kohdasht and vernalization saturation in cheyyene at 42nd-d of exposure to 4°c. the results of lt50 proved the maximum cold tolerance on either 42nd-d in cheyyene (-17°c), or -2°c in kohdasht (fixed at cold treatment period). the relationship of cholorophyll fluorescence, chlorophyll content (spad), proline and total carbohydrates with cold tolerance were studied. the results indicated that cholorophyll fluorescence was less influenced in cheyyene than in kohdasht in response to cold stress. vernalization cold caused significant 30% decline in chlorophyll content in kohdasht and 36% increase in cheyyene cultivar on vernalization saturation time (day 42). at this time, 3- and 2-fold cold-induced accumulations of proline and total carbohydrates, respectively were detected in cheyyene compared to kohdasht cultivar. in conclusion, such physiological results verified the advantageous response to cold of vernalization required-cultivar in comparison with non-vernalization required-cultivar.