Evaluation of Biochemical and Physiological Responses of Seven Olive Cultivars in Relation to Freezing Tolerance

Temperature is one of the most important factors limiting the production and distribution of olive. Different olive cultivars show diverse responses to low temperature and so, the selection of cold tolerant cultivars is the most effective method to avoid frost damages. The main purpose of this study was to compare freezing tolerance of seven olive cultivars and to investigate the relationship between freezing tolerance and maximum quantum yield of PSII, soluble carbohydrates, malondialdehyde, stomatal density, leaf tissue density and leaf relative water content during cold acclimation. After measuring the chlorophyll fluorescence, leaf samples from each cultivar were collected and were divided into two groups. The first group was subjected into different freezing temperatures (0, -5, -10, -15, -20 and -25 °C) for 12 h, in order to determine their freezing tolerance. The second group was used for some biochemical and physiological parameters analysis. The results showed that there was a significant difference among olive cultivars with respect to freezing tolerance. The highest freezing tolerance was related to ‘Amphisis’, ‘Shengeh’ and ‘Conservallia’ cultivars (LT50 -13.14, -11.72 and -11.20 °C, respectively) and the lowest tolerance to the ‘Rashid’ (LT50 - 6.90 °C). In freezing tolerant cultivars, Fv/Fm, soluble carbohydrates and leaf density were more than other cultivars, indicating a positive relationship with freezing tolerance. The concentration of malondialdehyde, stomatal density and relative leaf water content in freezing tolerance cultivars such as ‘Amphisis’, ‘Shengeh’ and ‘Conservallia’ were less than freezing sensitive cultivar of ‘Rashid’.