Evaluation of Freezing Tolerance in Four Olive Cultivars (Native and Foreign) Based on Physiological Indicators under Cold Acclimation Conditions

In order to evaluate the freezing tolerance of olive cultivars (native and foreign), a factorial experiment based on completely randomized design with three replications was carried out under controlled conditions. The investigated factors included cultivar (Zard, Roghani, Koroneiki, Mission), temperature (-18, -20 °C) and frost duration (24 and 48 hours). In addition, the effects of double and triple interactions among cultivar were significant for these two physiological traits. By applying freezing temperatures for 24 and 48 hours, the results showed that the electrolyte leakage percentage and the amount of free proline increased and decreased respectively with decreasing temperature in all studied cultivars; however, the changes of proline were more regular than the electrolyte leakage. So that at -18 °C, the highest and lowest percentage of electrolyte leakage was related to Koroneiki and Roghani cultivars, respectively and at -20 °C, the following descending order was obtained for the percentage of electrolyte leakage: Koroneiki > Mission- Roghani> Zard. However, in similar conditions, the highest and lowest amount of proline belonged to Zard and Koroneiki cultivars respectively. The proline capability to discriminate the studied cultivars was higher. So, based on the results obtained, cultivar Zard may be suggested as the preferable and superior cultivar for cultivation in areas under freezing stress.