Journal of Crop Breeding

   Sesame (Sesamum indicum L.) is one of tropical plants that sensitive to cold. In order to evaluate the tolerance of different genotypes of sesame to cold stress and effect of cold on their physiological characteristics, an experiment was conducted using a completely randomized design on ten genotypes including Varamin, Qa’im, Ultan, Yekta, Dashtestan 2, Darab 1, Naz Takshakheh, Naz Chandshakheh, Jahad and Nishapur with three replications. The genotypes exposed three days in 8˚C and the leaf samples were prepared at 0 (pre-stress), 6, 12, 24 and 48 hours. The highest amount of chlorophyll a was measured in Naz Chandshakheh, and the lowest amount was in Varamin and then was in Nishapur genotype after 48 hours. About chlorophyll b, the Naz Chandshakheh and after it, Jahad genotypes had the highest and the Nishapur genotype had the lowest amount after 72 hours. The amount of carotenoids, just in time zero and the beginning of stress (6), a significant difference was observed among genotypes and with advancing the stress, changes in ten genotypes carotenoids in such a way that no significant differences were found. The process of proline changes was incremental and proline accumulation found during cold stress in all genotypes. The difference between genotypes in stress and non-stress (time zero) conditions was significant and the highest amount of proline accumulated in Naz Chandshakheh and the lowest found in the Nishapur genotype at all times. The changes of malondialdehyde (MDA) was different in the genotypes at all times and the Nishapur and then Darab 1 genotype had the highest and the Naz Chandshakheh genotype had the lowest amount of MDA at the end of cold stress duration, which represent respectively the maximum and minimum damage to the membrane. The cold stress leads to loss of intracellular water of leaves and thus, the concentration of photosynthetic pigments increased. On the other hand, the lost water is used to interactions, such as the synthesis of proline and its levels has increased under the stress. As well as damage to the membrane, causing exit substances such as MDA that due to these factors finally, the Naz Chandshakheh and the Nishapur genotype introduced respectively as cold tolerant and cold sensitive cultivar.