Evaluation of freezing tolerance in olive cultivars by stomatal density and freezing stress

Selection of frost tolerant cultivars and understanding the mechanisms of frost hardiness could help to improve freezing resistance in olive plants. Olive cultivars may differ in frost hardiness due to differential survival of specific organs. The aim of this study was to screen different olive cultivars based on their stomatal density and metabolic modifications under cold conditions. The ‘Zard’ cultivar had the lowest while ‘Derak’ had the highest stomatal density, respectively. In another experiment, where entire potted olive plants were subjected to freezing stress (0, -6, -12 and -18 ˚C), ‘Zard’ and ‘Dehghan’ were found to be the most tolerant cultivars. They showed the lowest starch content, ionic leakage and wood injury. They also had the highest reducing sugar, phenolic and proline contents among studied cultivars. We concluded that ‘Zard’ and ‘Dehghan’ are the most tolerant cultivars and ‘Derak’, ‘Dakal’ and ‘Shiraz’ are the most sensitive cultivars to freezing injury.